Reduction and Discussion of the Deviations of the Compass Observed on Board of All the Iron-Built Ships, and a Selection of the Wood-Built Steam-Ships in Her Majesty's Navy, and the Iron Steam-Ship 'Great Eastern'; Being a Report to the Hydrographer of the Admiralty

XX. Reduction and Discussion of the Deviations of the Compass observed on board of all the Iron-built Ships, and a selection of the Wood-built Steam-ships in Her Majesty's Navy, and the Iron Steam-ship 'Great Eastern'; being a Report to the Hydrographer of the Admiralty. By Frederick J. Evans, Esq., Master R.N., Superintendent of the Compass Department of Her Majesty's Navy. Communicated by Captain Washington, R.N., F.R.S., by command of the Lords Commissioners of the Admiralty. Received May 5,—Read June 21, 1860. Sir, London, April 18, 1860. In compliance with the general instructions I received from you on my appointment, to observe carefully the working of the Mariner's Compass in the ships of Her Majesty's Navy, and especially in iron vessels, both for the security of their navigation and the aid of science, I now beg leave to submit for your consideration the following Report treating on these points, and in which is embodied an analysis of the magnetic character of all the iron-built ships in Her Majesty's Navy, as also of several of the wood-built steam-ships. In directing attention to this analysis, as given in a series of Tables, it is necessary to advert to the observations on which it is based, as resulting from a general system pursued in the Royal Navy. On the foundation of the Compass Department in 1843, a periodical examination of the disturbance caused by the iron on the compass in each ship,—or the deviation of the compass as it is now familiarly known to seamen,—was directed to be made by the Lords Commissioners of the Admiralty; the records of this examination are duly preserved in the Hydrographic Office, and have been employed in this investigation. The compass specially selected at this period (and since retained with a few modifications) for the navigation of Her Majesty's ships, and with which all observations for the deviation are made, and to which the steering or binnacle compasses of the ship are referred, is well known as the "Admiralty Standard*." This compass is solidly fixed in the middle line of the ship, within the limits of the quarter-deck; generally at a distance from the stern varying from one-fifth to one-tenth of the vessel's length, and raised sufficiently high from the deck to secure bearings of terrestrial objects above the gunwales or bulwarks, which ensures a height varying from about 4 feet 6 inches to 6 feet 6 inches; an essential condition of its arrangement being that it is kept as free from the immediate vicinity of iron as the nature and equipment of the vessel will permit. The details of all the essential parts of the Admiralty Standard compass, including * A brief description of this compass, and the chief points in its construction, is appended. the cards and needles, are uniform throughout; the intensities of the latter being remarkably so, and also permanent over long periods of time: the observations made with this compass are therefore strictly comparable, and it will be understood that the results given in this Report, except when specified to the contrary, and the inferences arising therefrom, must be considered as applying to a compass in the various details of position and structure just described. The analysis of the deviations of the compass in iron-built vessels, embraces forty-two ships of the Royal Navy; and including the wood-built screw and paddle-wheel steam-vessels, as also the deviations observed in various parts of the steam ship 'Great Eastern' during her experimental trip to Portland in the autumn of 1859, has involved a computation of nearly two hundred and fifty Tables. In order to render the analysis complete as a standard of reference, there is appended certain statistical information relating to each vessel, including tonnage, and exact position and height of standard compass: these details will be found necessary in a critical examination of the magnetic characteristics of ships in general. In the analysis of the Deviation Tables, I have employed Mr. Archibald Smith's formula for computing the magnetic coefficients, as deduced from Poisson's General Equations given in the Supplement to the "Practical Rules for ascertaining and applying the Deviations of the Compass caused by the Iron in a Ship," furnished to Her Majesty's Ships; and also in the Philosophical Transactions for 1846. In this formula the deviation ($\delta$) of the compass on board ship, reckoned positive when the north point of the needle deviates to the east, is given by the following expression: $$\delta = A + B \sin \zeta' + C \cos \zeta' + D \sin 2\zeta' + E \cos 2\zeta',$$ A, D, E being constants depending only on the amount, quality, and arrangement or position of the iron in the ship; B and C depending on these, and also on the magnetic dip and horizontal intensity; and $\zeta'$ the azimuth (by disturbed compass) of the ship's head, reckoned from the magnetic north to the east. This formula is only approximate; but is sufficiently correct when the deviation does not exceed about $20^\circ$. The accurate formula involves calculations too laborious to be applied to ordinary cases. Without entering on the nature and action of the magnetic forces which cause the deviation of the compass on board ship,—to be found in the works to which I have alluded, as also in the introduction to Dr. Scoresby's late Voyage round the World for magnetical research, edited by Mr. Archibald Smith,—further than to attach a physical meaning to the coefficients for practical elucidation, it is necessary to premise that the investigations of the Astronomer Royal* are in accord with the general terms * "Account of Experiments on Iron-built ships, instituted for the purpose of discovering a correction for the deviation of the Compass produced by the Iron of the ships," Philosophical Transactions, Part I. 1839. "Discussion of the observed Deviations of the Compass in several ships, Wood-built and Iron-built: with a General Table for facilitating the examination of Compass Deviations," by G. B. Airy, Esq., Astronomer Royal, Philosophical Transactions for 1856. of this formula; observing, that in those investigations the coefficients A and E are eliminated by the assumption that the soft iron is symmetrically distributed on each side of the fore-and-aft line of the ship. The meaning of the several coefficients is as follows: A is a constant deviation, real or apparent; + if easterly deviation is in excess, — if westerly; when real, it arises from the induction of the horizontal force of the earth on masses of soft iron unsymmetrically distributed; when only apparent, as in nearly every case recorded, it is considered due to prism, or index error of the compass on board, or of the compass employed on shore in obtaining reciprocal bearings, as also local disturbance of the latter; and, when the deviation has been observed by the bearing of a distant object, that the latter has been imperfectly determined. B and C are due to the combined effects of the permanent magnetism of the hard iron; the deviation produced by which varies inversely as the horizontal force at the place, and that induced by the vertical part of the earth’s force on the soft iron in the ship, the deviation produced by which varies as the tangent of the dip. This deviation has been termed “polar-magnet” by the Astronomer Royal, and “semicircular” by Mr. A. Smith, from the nature and appearance of the curve when graphically delineated. B represents that part of the combined attraction acting in a fore-and-aft direction; + if before the compass, — if abaft it; that is, the north end of the needle is attracted to the bow in the former case, and to the stern in the latter. C is that portion of the combined attraction acting in an athwart-ship direction; + if the north end of the needle is drawn to the starboard side, — if drawn to the port side of the ship. D and E, known as the permanent coefficients, from their (theoretically considered) unchanging value in all magnetic latitudes, are due to the horizontal induction of the soft iron in the ship, and produce a “quadrantal” deviation; the term multiplied by D having its four maxima at the intercardinal points, and that by E at the cardinal points. The values of D are considered by theory to arise from masses acting in a fore-and-aft, or transverse direction; + from those before or abaft, — from those on either side. E is in general so small as to be practically unimportant. Tables of Magnetic Elements of various Ships in Her Majesty’s Navy, Iron and Wood-built. The results of the analysis of the Tables of Compass Deviation are thus arranged: Table I. The iron-built vessels arranged according to tonnage: this analysis includes every Deviation Table of such vessels recorded in the Admiralty. Table II. Includes the floating batteries; one iron-built, and the others wood-built plated with iron. Table III. A selection from the wood-built screw steam-vessels, embracing those of large, medium, and small dimensions. Table IV. A selection from the wood-built paddle-wheel steam-vessels, embracing vessels of various dimensions. The selected examples of Tables II. and III. must be understood as adopted to represent the general types of their classes: the examples in these Tables, of deviations observed on Foreign stations, are selected from the evident skill and care that has been bestowed on the observations, and from their perfect illustration of the general nature of the magnetic change in wood-built steam-ships. Table V. The magnetic coefficients of the steam-ship Great Eastern, as observed in various parts of the vessel by myself, conjointly with Mr. Rundell, the Secretary to the Liverpool Compass Committee. The general tabular arrangement it is considered requires little further explanation than the titles of the various columns convey. The column "Ship's force to head" is the natural sine of the corresponding value of the coefficient B, and is in fact the proportion of the ship's force to head, to the earth's horizontal force. The column "Ship's force to starboard" is the natural sine of the corresponding value of the coefficient C, and is the proportion of the ship's force to the starboard side, to the earth's horizontal force. The resultant of B and C is the ship's force, and is in its direction $\left[ \tan^{-1} \frac{C}{B} \right]$ and amount $\left[ \sqrt{B^2 + C^2} \right]$ the equivalent of the "true starboard angle" (measured from the bow round by the starboard side to the bow again), or "neutral position;" and of the "modulus" of polar-magnet deviation in Mr. Airy's paper in the Philosophical Transactions for 1856. It will be observed that in the results obtained from Deviations observed on Foreign stations (noted in italics), the total force of the ship is given in two lines, the upper line being the proportion of the ship's force to the horizontal force of the earth at the place, the lower line being the proportion of the ship's force to the horizontal force in England, so as to allow a comparison to be made of the absolute force of the ship at various stations. For convenience, 1·000 has been adopted to represent the value of the earth's horizontal magnetic force at the several English ports where Her Majesty's ships are usually swung, viz. Greenhithe, Sheerness, Portsmouth, and Plymouth: for other stations I have adopted those given by Mr. Airy in the paper of 1855 alluded to; and for several places not included in his discussion, reference has been made to the chart of Absolute Magnetic Intensity by General Sabine*, employing for the reduction to the horizontal component, the most recent determinations of the magnetic dip with which I am acquainted. A comparative Table of the foregoing elements, with the horizontal force as given by Gauss in his 'Atlas des Erdmagnetismus,' reduced to the same unit of measure, is appended, as being probably of use in any future inquiry or discussion. I now proceed to direct attention to various features exhibited in the several Tables, * Keith Johnson's 'Physical Atlas,' 2nd edition. and shall venture to suggest what would appear from fair inferences to be the leading principles of the magnetism of the ships included therein, and their practical application. It has been deemed unnecessary to introduce an analysis of the compass deviations of wood-built sailing vessels; as, whether as ships of war with batteries of guns, or merchant vessels carrying cargo,—always excepting iron,—their deviations are small in amount, and arising in the aggregate from induced magnetism. An intercomparison of the magnetic coefficients of iron and wood-built steam-ships is of greater importance in the investigations of the laws affecting the former, than would at first appear: the special points elicited are— That D, which in the iron vessel ranges in value from $+1\frac{1}{2}^\circ$ to $+6^\circ$ and $7^\circ$ (the Liverpool Compass Committee recording even a point or $11^\circ$), seldom exceeds $+1^\circ$ in wood screw-ships, with not unfrequently a small minus sign in these vessels, and $+1\frac{1}{2}^\circ$ in the wood paddle-wheel steam-ships. A and E appear common in character and value in all the classes of vessels enumerated. B and C thus differ:—In the wood-built vessel (in Great Britain) B is $+$ whenever the engines are before the compass, and C is always small in value. In the iron-built vessel, B, irrespective of the machinery, is either $+$ or $-$ as the ship's head while building was south or north; and C may be large in value, either $+$ or $-$; B nearly vanishing as the ship's head while building deviated from the magnetic meridian and approached the east or west points of the compass*. Taking therefore the relative tonnage, horse-power, and position of the standard compass in each class of vessel, wood and iron, a judgment can be formed of the comparative magnetic effects of the engines and boilers, apart from the hull or hammered fabric of the iron ship. Several examples occur in the Tables; from which we may infer, (1) that in an iron vessel built in England, head south, the north end of the needle is drawn to the bow, or B is positive. The steam machinery has the same effect; B therefore as due to the hull, is increased in amount. (2) In an iron vessel built head to the north, the north end of the needle is drawn to the stern, or B is negative; the steam machinery will in this case tend to diminish the value of this coefficient; and on reference to Table I. it will be observed that, as a rule, those vessels with B positive have, taking size and other conditions of compass position into consideration, large compass deviations. But what are the combined effects of steam machinery and hull on a great change of geographic position, or in high south magnetic latitudes? An examination of the several Tables elicits some valuable information on this important point. * The connexion between the direction of the ship's keel and head while building as referred to the magnetic meridian, and the direction and strength of her magnetic polarity, so fully experimented on by the late Dr. Scoresby and the Liverpool Compass Committee, is, I consider, fully confirmed; and there will be added to this Report the magnetic lines of the 'Great Eastern,' as another example of this remarkable feature of an iron ship's magnetism. Referring to the magnetic changes of the wood-built vessels (screw or paddle) in the progress of their respective voyages to, and in the southern hemisphere, of which there are several good continuous examples, it is evident that the coefficients B and C are dependent in their change chiefly on the alteration of the magnetic dip, and that the horizontal intensity is a minor element of disturbance; it may therefore be inferred as a general rule, that in steam machinery, permanent magnetism bears but a small proportion to inductive. This appears sufficiently from examples in Tables III. and IV.; as also that, as in the case of wood-built sailing vessels (discussed by General Sabine in the Philosophical Transactions for 1849*), the wood steam-ship’s magnetism, on rapid changes of geographic position, falls short of, or “lags behind,” the amount theoretically due to changes of magnetic latitude. The wood screw-ships Plumper and Highflyer† are instructive examples of the “lagging behind” of their magnetism; in the former case, on the ship’s arrival at Vancouver Island, the semicircular deviation was much in arrear of the value due to the magnetic dip, as compared with that originally obtained in England. After an interval of sixteen months, on the ship being reswung in the same locality, which she had not quitted, the deviations exceeded the original amount observed in England, approximating to the value due to the increased magnetic dip at Vancouver Island. Similar features are exhibited in the Highflyer employed in the China seas. We have now to consider the magnetic nature of the hull of the iron vessel combined with the steam machinery; and in stating here the fact, of the former being, in the majority of the vessels investigated, highly permanent and but slightly inductive, in contradistinction to the steam machinery, I am only anticipating what will be hereafter given in proof from examples in Table I. The position of the standard compass with reference to the steam machinery in an iron vessel, has therefore an important bearing practically and theoretically; for if it is placed in proximity to the funnel, which may be considered as the zero or measuring point for the machinery in general, the inductive magnetism of the machinery is superadded on the subpermanent magnetism of the hull, and complicates the question apparently beyond research. An instructive practical example of this condition is afforded in the case of the ‘Vulcan’ iron ship: in this vessel the steam machinery is further aft than is usual in ships either of the Navy or of the mercantile marine; and it will be observed that the standard compass is only 27 feet distant from the funnel, and is elevated on the poop-deck nearly to the level of the top of the latter. Viewing the nature of the Vulcan’s hull under the conditions of permanent magnetism, the maximum deviation, or ship’s force, * Contributions to Terrestrial Magnetism, Part IX. † Commanded respectively by Captains George H. Richards and Charles F. Shadwell, C.B. The labour and attention bestowed by these officers in the determination of the compass deviations of their ships, and the consequent value of the results to the practice of navigation, and the theory of a ship’s magnetism, are worthy of especial record. when at the Cape of Good Hope, should have been reduced in the inverse proportion of 1·000 to 1·174, or about one-sixth, whereas by observation it had more than doubled: the polarity of the funnel and machinery, following the changes of magnetic dip (the vessel was some months employed in high south magnetic latitudes), was reversed, and thus their force of magnetism (−B) was added to that of the hull of the ship (−B also), instead of being subtracted from it, as had been the case in England. The Simoom, a nearly sister vessel to the Vulcan, but with +B, and also observed at the Cape of Good Hope, has the conditions reversed, the semicircular deviation being smaller than its theoretical value, for the opposite reason; viz. that the force of the machinery which had been added to that of the hull in England, changing its sign, was subtracted from it at the Cape of Good Hope. On the Nature of the Magnetism in Iron-built Ships. The magnetic influence of steam machinery having been reviewed, the nature of the magnetism of iron-built ships can be entered on free, to a certain extent, of conditions arising from this extraneous source of compass error, and those examples fairly eliminated where it tends to embarrass the discussion. The investigation of the coefficient D, or the disturbance arising from the horizontal induction of the soft iron in the ship, when extended over the numerous examples recorded in Table I., offers several novel and suggestive points of inquiry: the chief characteristics are,— 1. That it has invariably a positive sign, causing an easterly deviation in the N.E. and S.W. quadrants, and a westerly deviation in the S.E. and N.W. quadrants. 2. That its amount does not appear to depend on the size or mass of the vessel, or direction when building, or on the iron beams. 3. That a gradual decrease in amount has occurred, when examined over a number of years, in nearly every vessel that has been reviewed. 4. That the value remains unchanged in sign and amount, on changes of geographic position, confirming theoretical deductions. 5. That a value for this coefficient, not exceeding 4°, and ranging between that amount and 2°, may be assumed to represent the average or normal amount in vessels of all sizes. The following examples support these propositions:— 1. The value not depending on the size of the vessel. | Great Eastern, of 22,000 tons | +4° 8' | | Himalaya, ,, 3,453 ,, | +3° 18' | | Assistance, ,, 1,820 ,, | +3° 36' | | Trident, of 850 tons | +3° 26' | | Oberon, ,, 649 ,, | +3° 23' | | Onyx, ,, 292 ,, | +3° 42' | As also, that the effect of iron beams, which has been assumed as a large element of disturbance, cannot be traced. Assistance . . . 1820 tons, iron beams . . +3° 36' Trident . . . . 850 tons, wood beams . . +3° 26' Industry . . . . 638 tons, iron beams . . +2° 40' Oberon . . . . 649 tons, wood beams . . +3° 27' Bloodhound . . . 378 tons, iron beams . . +3° 40' Sharpshooter . . 503 tons, wood beams . . +4° 32' To establish the effect of iron beams more fully, I carried out a series of experiments on board H.M.S. Supply; and from the results it is to be inferred that their magnetic character is identical with that of the hull of the ship; being dependent, as regards polarity and permanency of magnetism, on the direction of the ship when building, and the nature of the iron. The uniformity of the quadrantal deviation of the compass, when placed in various positions and at different heights from the deck, is thus shown: | ft. | in. | |-----|-----| | In middle line of the 'Supply,' 28 feet from stern, 5' 0" high from deck | +2° 38' | | " 19" 5" 2" | {+2° 15' +2° 37' } | | " 12" 3" 10" | +2° 55' | Placed 22 feet from stern, 3 feet from middle line of deck, and 3' 9" high +2° 56' Placed 13 feet from stern, 8 feet from middle line of deck, 2 feet from the iron top side, and 1 foot 8 inches high +2° 13' The polar-magnet or semicircular deviation varied under these conditions from 15° to 45°. Elevation of the compass above an ordinary height from the deck necessarily diminishes the amount of quadrantal deviation, as in mast-compasses*; but within the ordinary limits, or from 2 to 6 feet from the deck, the foregoing examples show that the value is not affected. Another example was also afforded in H.M.S. Assistance, where the raising the standard compass from 4 feet 5 inches to 6 feet 4 inches above the iron beams, which diminished the "semicircular" deviation from 17° 40' to 15°, had no perceptible effect on the "quadrantal," the values of D being respectively +3° 35' and +3° 36'. Mast-compass, Standard compass, 45 feet from deck. 5 feet from deck. * Great Eastern River Thames ............... +1° 32' ............... +4° 21' Portland .................... +1° 30' ............... +4° 44' Holyhead .................... +1° 0' ............... +4° 8' H.M.S. Trident, mast-compass elevated 48 feet from the deck, D—1° 8': this is the only example that has come under my investigation of a minus sign. It is the effect which would be produced if the soft iron can be considered as collected in two masses,—one near the bow, the other near the stern. 2. The gradual decrease in the value of D is well marked in those ships in which the position of the compass has remained unchanged, and direct comparison has been thus afforded. | Ship | Years | Decrease from | To | |------------|-------|---------------|----| | Himalaya | 4½ | 3 51 | 3 18 = 0 33 | | Urgent | 4 | 2 58 | 2 12 , 0 46 | | Simoom | 7¾ | 3 57 | 3 25 , 0 32 | | Vulcan | 8½ | 3 20 | 2 48 , 0 32 | | Birkenhead | 4 | 2 53 | 2 12 , 0 41 | | Trident | 13 | 4 03 | 3 26 , 0 37 | | Triton | 9½ | 4 02 | 2 37 , 1 25 | | Supply | 5¼ | 3 40 | 2 15 , 1 25 | | Bloodhound | 10 | 3 40 | 2 31 , 1 9 | | Jackal | 14 | 4 57 | 3 01 , 1 56 | | Myrmidon | 9¼ | 3 23 | 2 45 , 0 38 | | Harpy | 14 | 2 54 | 2 32 , 0 22 | | Lizard | 13 | 3 49 | 3 4 , 0 45 | | Onyx | 4 | 3 42 | 3 26 , 0 16 | | Dover | 5½ | 2 38 | 2 23 , 0 15 | 3. In assuming the normal amount of quadrantal deviation in iron steam-ships as from 2° to 4°, it will be seen, from the accompanying analysis, that thirty-four of the forty-two ships in Her Majesty's Navy, or 75 per cent., are included in this condition, thus: Quadrantal deviation, between 1° and 2°, 2 vessels, of 1391 and 462* tons. - 2°, 2½°, 1°, 164 tons. - 2°, 3°, 11°, 1981 to 180 tons. - 2½°, 3¼°, 10°, 1764, 270 tons. - 3°, 4°, 10°, 3453, 292 tons. - 3½°, 4½°, 3°, 1980, 503 tons. - 3°, 5°, 2°, 440, 340 tons. - 4°, 5°, 1°, 267 tons, as also Gt. Eastern. - 6°, 7°, 2°, 1954† to 267 tons. Two questions of import here arise:—Are the results of this analysis to be deemed conclusive? and, if so, under what conditions do large quadrantal deviations occur? It will be remembered that the two earliest iron vessels experimented on by Mr. Airy,—the 'Rainbow' in 1838, and the 'Ironsides' in 1839,—vessels probably in those * A sailing vessel. † A floating battery. early days considered experimental, and built of the best material, had very small quadrantal deviations, viz. $1^\circ$ and $1^\circ 6'$ respectively; indeed the Astronomer Royal experienced difficulty in tracing the effects of terrestrial induction. Bearing these facts in view, and taking further into consideration that in building Government vessels stringent conditions of contract as to soundness of material are enforced, and strict supervision exercised, it may be fairly assumed that the amount given of $2^\circ$ to $4^\circ$ represents the average condition of a well-built ship of the best or superior iron. On the other hand, can the inference be drawn that an iron ship with large quadrantal deviation implies inferior material being used in her construction? Two of the most disastrous and fatal shipwrecks on record have occurred to iron-built vessels, whose magnetic characters are perfectly known. H.M.S. Birkenhead, whose permanency of magnetism (Table I.) was especially constant, and quadrantal deviation small,—$2\frac{1}{4}^\circ$+ a short time prior to her loss,—may be considered as the type, magnetically, of a "hard" iron-built ship: the Royal Charter, with a quadrantal deviation of $6^\circ$, and whose sub-permanent magnetism fluctuated more than any vessel with whose records I am acquainted, may be considered as the type, magnetically, of a "soft" iron-built ship. It will be recollected that in the wreck of these vessels under their varied circumstances, both parted amidships; the Royal Charter so suddenly and rapidly, as to invite serious attention to various points of her construction. It is difficult to draw any comparative conclusions from these two cases, but they are placed in juxtaposition as grounds for further inquiry as to the connexion between the amount of quadrantal deviation and the nature of the iron of the ship; and it will be remarkable and not less useful, if, in the prosecution of such inquiry, it can be established that the relative qualities of the material used in iron ship-building can be discriminated by the subtle agency of the ship's compass-needle. On the Coefficients B and C in Iron-built Ships, or that part of the Compass-disturbance arising from the permanent magnetism of "hard" iron, and that induced by the vertical part of the earth's force on the "soft" iron in the ship. On examination of Table I., it is at once observed that in the majority of examples therein given, a permanency of magnetism exists so little affected by changes of geographic position, as materially to confirm the views entertained by the Astronomer Royal in his earliest discussion (1838), that the effect of transient induced magnetism in iron-built ships is very small comparatively. The absence of irregular fluctuations, and the gradual diminution of the ship's force, analogous to the gradual decrease of the quadrantal deviation, are notable features; and apparently the general permanency is but little influenced by concussions from the sea, or from the repairs in dock, which necessarily must have occurred during the several years over which the observations extend. The gradual diminution of the ship's magnetic force is shown in the following examples, all determined in English ports, and where it has been ascertained that, from the compass remaining in the same position, the results are comparative. The column "semicircular" deviation has been added to show the practical distur- bance on the compass at its maximum. ### Himalaya. | Year | Direction | Amount | Semicircular deviation | |------|-----------|--------|------------------------| | 1855 | 182 | 0·275 | 16° 0' | | 1856 | 182 | 0·243 | 14° 5' | | 1859 | 169 | 0·248 | 14° 25' | ### Urgent. | Year | Direction | Amount | Semicircular deviation | |------|-----------|--------|------------------------| | 1855 | 175 | 0·215 | 12° 25' | | 1856 | 170 | 0·183 | 10° 35' | | 1857 | 158 | 0·163 | 9° 25' | | 1859 | 170 | 0·151 | 8° 45' | ### Simoom. | Year | Direction | Amount | Semicircular deviation | |------|-----------|--------|------------------------| | 1852 | 340 | 0·367 | 21° 35' | | 1852 | 340 | 0·367 | 21° 35' | | 1857 | 355 | 0·326 | 19° 0' | | 1859 | 4 | 0·316 | 18° 30' | ### Megæra. | Year | Direction | Amount | Semicircular deviation | |------|-----------|--------|------------------------| | 1851 | 190 | 0·232 | 13° 25' | | 1852 | 150 | 0·238 | 13° 45' | | 1857 | 162 | 0·219 | 12° 40' | ### Birkenhead. | Year | Direction | Amount | Semicircular deviation | |------|-----------|--------|------------------------| | 1847 | 205 | 0·264 | 15° 15' | | 1847 | 206 | 0·265 | 15° 20' | | 1848 | 206 | 0·260 | 15° 5' | | 1850 | 207 | 0·264 | 15° 15' | | 1851 | 206 | 0·267 | 15° 30' | ### Trident. | Year | Direction | Amount | Semicircular deviation | |------|-----------|--------|------------------------| | 1846 | 3 | 0·845 | 20° 10' | | 1848 | 359 | 0·359 | 21° 0' | | 1849 | 360 | 0·316 | 18° 36' | | 1852 | 352 | 0·342 | 20° 0' | | 1856 | 351 | 0·376 | 22° 5' | | 1859 | 2 | 0·320 | 18° 40' | ### Caradoc. | Year | Direction | Amount | Semicircular deviation | |------|-----------|--------|------------------------| | 1848 | 199 | 0·230 | 13° 20' | | 1855 | 191 | 0·193 | 11° 10' | ### Triton. | Year | Direction | Amount | Semicircular deviation | |------|-----------|--------|------------------------| | 1848 | 178 | 0·207 | 11° 55' | | 1852 | 198 | 0·142 | 8° 10' | ### Oberon. | Year | Direction | Amount | Semicircular deviation | |------|-----------|--------|------------------------| | 1847 | 294 | 0·266 | 15° 25' | | 1851 | 295 | 0·230 | 13° 20' | ### Industry. | Year | Direction | Amount | Semicircular deviation | |------|-----------|--------|------------------------| | 1854 | 13 | 0·247 | 14° 20' | | 1856 | 13 | 0·256 | 14° 50' | | 1858 | 358 | 0·230 | 13° 20' | | 1858 | 354 | 0·182 | 10° 30' | | 1859 | 360 | 0·185 | 10° 40' | ### Sharpshooter. | Year | Direction | Amount | Semicircular deviation | |------|-----------|--------|------------------------| | 1848 | 177 | 0·126 | 7° 15' | | 1850 | 180 | 0·105 | 6° 5' | | 1852 | 180 | 0·280 | 16° 15' | | 1857 | 189 | 0·235 | 13° 35' | ### Bloodhound. | Year | Direction | Amount | Semicircular deviation | |------|-----------|--------|------------------------| | 1845 | 351 | 0·256 | 14° 50' | | 1847 | 351 | 0·209 | 12° 5' | | 1851 | 347 | 0·219 | 12° 40' | | 1855 | 350 | 0·207 | 12° 0' | ### Jackal. | Year | Direction | Amount | Semicircular deviation | |------|-----------|--------|------------------------| | 1845 | 353 | 0·288 | 16° 45' | | 1849 | 344 | 0·266 | 15° 25' | | 1854 | 329 | 0·316 | 18° 25' | | 1859 | 339 | 0·262 | 15° 10' | ### Lizard. | Year | Direction | Amount | Semicircular deviation | |------|-----------|--------|------------------------| | 1845 | 351 | 0·236 | 13° 40' | | 1853 | 3 | 0·188 | 10° 50' | | 1858 | 5 | 0·172 | 9° 55' | ### Firequeen. | Year | Direction | Amount | Semicircular deviation | |------|-----------|--------|------------------------| | 1847 | 320 | 0·210 | 12° 10' | | 1852 | 329 | 0·197 | 11° 20' | ### Fairy. | Year | Direction | Amount | Semicircular deviation | |------|-----------|--------|------------------------| | 1850 | 355 | 0·233 | 13° 30' | | 1852 | 357 | 0·202 | 11° 40' | | 1858 | 10 | 0·201 | 11° 35' | ### Princess Alice. | Year | Direction | Amount | Semicircular deviation | |------|-----------|--------|------------------------| | 1844 | 2 | 0·257 | 14° 55' | | 1850 | 358 | 0·225 | 13° 0' | | 1855 | 348 | 0·213 | 12° 20' | ### Torch. | Year | Direction | Amount | Semicircular deviation | |------|-----------|--------|------------------------| | 1846 | 340 | 0·206 | 11° 50' | | 1852 | 356 | 0·186 | 10° 45' | * Position of the compass changed since the earlier determinations. Examples of permanency of ship's force on changes of geographic position are exhibited in the following vessels; in which, for the sake of comparison, the modulus has been multiplied by the horizontal intensity at the place. ### Urgent | Year | Direction | Amount | |----------|-----------|--------| | 1855 | England | 176 | 0·215 | | 1855 | Malta | 184 | 0·189 | | 1856 | England | 170 | 0·183 | ### Megæra | Year | Direction | Amount | |----------|-----------|--------| | 1852 | England | 150 | 0·238 | | 1853 | Antigua | 145 | 0·213 | | 1857 | England | 162 | 0·219 | ### Triton | Year | Direction | Amount | |----------|-----------|--------| | 1852 | England | 198 | 0·142 | | 1852 | Corfu | 200 | 0·142 | | * | 1857 | England | 213 | 0·178 | | * | 1858 | Fernando Po | 181 | 0·188 | ### Oberon | Year | Direction | Amount | |----------|-----------|--------| | 1851 | England | 295 | 0·230 | | 1856 | Malta | 297 | 0·201 | | * | 1858 | England | 323 | 0·180 | | * | 1858 | Monte Video | 303 | 0·179 | ### Bloodhound | Year | Direction | Amount | |----------|-----------|--------| | 1845 | England | 351 | 0·256 | | 1846 | Constantinople | 347 | 0·281 | | 1846 | Athens | 344 | 0·249 | ### Assistance | Year | Direction | Amount | |----------|-----------|--------| | 1857 | England | 129 | 0·259 | | 1858 | Canton | 119 | 0·274 | ### Adventure | Year | Direction | Amount | |----------|-----------|--------| | 1857 | England | 124 | 0·305 | | 1858 | Whampoa, China | 118 | 0·307 | ### Caradoc | Year | Direction | Amount | |----------|-----------|--------| | 1848 | England | 199 | 0·230 | | 1852 | Malta | 189 | 0·258 | | 1855 | England | 191 | 0·193 | | 1857 | Malta | 191 | 0·229 | | 1858 | Malta | 200 | 0·242 | ### Industry | Year | Direction | Amount | |----------|-----------|--------| | 1856 | Malta | 359 | 0·240 | | 1856 | England | 13 | 0·256 | ### Sharpshooter | Year | Direction | Amount | |----------|-----------|--------| | 1852 | England | 180 | 0·280 | | 1853 | Rio de Janeiro | ... | 0·253 | | 1857 | England | 160 | 0·235 | | 1857 | Isles de Los, Africa | 172 | 0·222 | ### Jackal | Year | Direction | Amount | |----------|-----------|--------| | 1845 | England | 353 | 0·288 | | 1846 | Athens | 355 | 0·274 | | 1847 | Lisbon | 352 | 0·260 | ### Trident | Year | Direction | Amount | |----------|-----------|--------| | 1846 | England | 363 | 0·345 | | 1847 | Malta | 357 | 0·359 | | 1848 | England | 360 | 0·359 | | 1852 | England | 353 | 0·342 | | 1852 | Rio de Janeiro | 351 | 0·368 | | 1856 | England | 351 | 0·376 | | 1857 | Ascension Island | 342 | 0·373 | | 1857 | Cape of Good Hope | 354 | 0·333 | | 1859 | England | 363 | 0·320 | ### Harpy | Year | Direction | Amount | |----------|-----------|--------| | 1854 | England | 5 | 0·152 | | 1857 | Malta | 352 | 0·166 | ### Wilberforce | Year | Direction | Amount | |----------|-----------|--------| | 1843 | England | 223 | 0·185 | | 1843 | River Gambia | 222 | 0·193 | ### Torch | Year | Direction | Amount | |----------|-----------|--------| | 1852 | England | 356 | 0·186 | | 1852 | Madeira | 348 | 0·153 | | 1852 | St. Vincent Island | 352 | 0·161 | | 1852 | Rio de Janeiro | 351 | 0·219 | | 1852 | Tristan d'Acunha | 337 | 0·189 | | 1852 | Cape of Good Hope | 3 | 0·190 | | 1853 | St. Paul's Island | 357 | 0·198 | | 1853 | Swan River | 358 | 0·182 | | 1853 | K. George's Sound | 352 | 0·214 | | 1856 | Australia | 3 | 0·246 | * Position of compass changed since the earlier determinations. The Torch is a special example. This vessel was sold out of Her Majesty's service at Sydney, after a continuous service of three years in Australia (1853 to 1856) in high south magnetic latitudes; in July 1856 she was chartered by the Colonial government of New South Wales to proceed to the northern coast of Australia to render assistance to an exploring expedition. The officer who had previously been in command, Lieut. Wm. Chimm, R.N., was the Government agent on this occasion, and on the passage, especially along the eastern shores of Australia, that officer made numerous observations for the Variation of the Compass (the direction of the ship's head being noted to each), which were transmitted to the Admiralty. From these observations, compared with the well-known variation in these seas, I was enabled graphically to construct a curve of deviation: the results are given, and are confirmatory of the general permanent nature of the ship's magnetism under circumstances which I apprehend are novel, and not without value in a theoretical discussion. The conclusions derived from a review of the foregoing results are not unimportant; and not the least of these in practical value, is that in an iron ship of ordinary dimensions, and of conditions similar to the examples quoted, a standard compass can be placed, the deviations of which will but little exceed those obtaining in wood-built steam-ships; and further, that on a change of geographic position, however great, these compass deviations will be within smaller limits, and can be approximately predicted. A divergence from these conditions will arise when the inductive magnetism of the hull or machinery predominates. If we may judge from the case of the Royal Charter, whose magnetic elements have been so ably discussed by various authorities, large quadrantal deviation and fluctuating sub-permanent magnetism (due to hull alone) are coexistent, and give rise to conditions of compass-disturbance which are beyond prediction, have hitherto baffled inquiry, and given a complexion to theoretical deductions varying as regarded from different points of view. Observations on the early changes of an Iron-built ship's Magnetism, illustrated by experiments in the Steam-Ship Great Eastern. The opinion has been long entertained, that the original magnetism of an iron-built ship, or that acquired in the process of building, undergoes a rapid change after launching, and that from this cause accidents have occurred to recently launched and hastily equipped vessels. The records of ships of the Royal Navy do not illustrate this subject. The unusual dimensions of the Great Eastern, and the interest attaching to the progress and success of so great an undertaking, pointed her out as a desirable ship to test in elucidation of various problems connected with the mariner's compass, and especially of the supposed early changes in the ship's magnetic force. Through the kindness of the Directors, and partly in the nature of assistance sought for by that body from the Lords of the Admiralty, I was enabled to make many observations, the results of which, so far as they relate to the early changes in the deviations of the compass, and the external magnetic lines of the ship, will be found in Table V., and an accompanying diagram in Plate XV. In the progress of building (18th August, 1857), I ascertained by astronomical bearings, with the known variation of the compass at the time, that the magnetic direction of her keel and head was S. 29° 50' E. A short time previous to the launching (November 1857), I also obtained the few results for the external magnetic lines, which will be found in the diagram. After launching, the Great Eastern was secured near Deptford dockyard, with her head S. 46° E. magnetic; differing only 16° from the original direction while building; considerable works, chiefly internally, were in progress till the time of quitting this anchorage. In August 1859, a few days prior to leaving the river, an extended series of observations for the development of the external magnetic lines (see diagram, Plate XV.) was obtained; which show that some alteration had taken place since the first approximate determination. On September 7th, 1859, the Great Eastern quitted Deptford on her preliminary trip to Portland, arriving at the latter port on the 10th. On the passage between these places, which included temporary anchorages at Purfleet and the Nore, every opportunity was embraced of determining the deviations of the compass at various selected stations in the ship which are marked in the diagram. The deviations whilst in the River Thames were determined by noting the difference between the bearing of the ship’s head, as astronomically determined (by the use of a repeating card, and prepared table of the sun’s bearings), and as denoted by the compass: a curve of deviations embracing each point of the compass was then graphically drawn through the general results. At Portland, lying within the breakwater, the correct magnetic bearing of St. Alban’s Head, a distant point of land, afforded ready means of determining the deviations as the vessel swung round at her anchor; and subsequently at Holyhead, where I proceeded again in conjunction with Mr. Rundell, similar means were adopted as at Portland by the bearing of a distant Welch mountain. As it was not possible to “swing” the Great Eastern, from her ponderous bulk, in the mode usually adopted under these circumstances with ordinary sized vessels, we were dependent on the changes of ship’s head arising from winds and tides: this necessarily occupied much time, and was the occasion of gaps being left in the curves of deviations obtained both at Portland and Holyhead, which required to be arbitrarily filled up. As these curves presented no anomalous differences from those of ordinary sized ships, but were marked by perfect regularity and consistency among the observations, these gaps were confidently completed. From a consideration of the magnetic character of the Great Eastern, it is apparent that the Admiralty Standard compass, as also the ship’s Standard compass, were placed in the best position with respect to the hull and machinery, both for experimental research and the navigation of the ship; indeed, from the vast amount of machinery and neces- sarily inductive material running nearly fore and aft the vessel, I am disposed to attach but little comparative value to any of the results except those of the Admiralty Standard compass, as it will be seen that the other compasses are influenced by the near proximity of steam funnels or iron masts. Directing attention to the changes in the magnetism of the ship as indicated by this compass, the gradual diminution of the ship’s force is marked at each successive period of observation, and also the constant tendency to attain a fore-and-aft direction. In the first five days, from Deptford to Portland, the force had diminished from $0.585$ to $0.480$, nearly one-fifth, or the semicircular deviation decreased from $35^\circ 50'$ to $28^\circ 45'$; the direction of force, or neutral points, approaching a fore-and-aft line $10^\circ$, or from $47^\circ$ on the starboard bow to $37^\circ$: it is here worthy of remark, that the general direction of the ship’s head for three days at Portland out of the five named, was N.W., or exactly opposite to her direction whilst lying at Deptford. The change at the expiration of the next six weeks, the ship in the interim having made the passage to Holyhead, with some trifling rough weather, still shows a diminution of force, and tendency to the fore-and-aft direction of the neutral points of disturbance: the former is reduced from $0.480$ to $0.390$, or about one-sixth (the corresponding semicircular deviation being $28^\circ 45'$ and $23^\circ 0'$); and the latter changed $5^\circ$, or from $37^\circ$ to $32^\circ$. The changes denoted by the mast and platform compasses do not follow the same progressive decrease and change of direction of ship’s force. To the less perfect observations of the mast-compass, arising from the difficulty of obtaining readings aloft, and from the friction of blunted pivots after a few weeks’ wear and tear, can be traced the probable causes for this instrument; the unfavourable but unavoidable position for the platform compass has been adverted to. The quadrant deviations of all the compasses show a decrease, so far confirmatory of the law that exists in the numerous vessels reviewed; but there is an anomaly detected by Mr. Airy* in the quadrantal disturbance of the Admiralty Standard compass worthy of record, viz. that it is larger in the quadrant from west to north; the position opposite to that in which the ship was built. | | 1st, or N.E. quadrant | 2nd, S.E. | 3rd, S.W. | 4th, N.W. | |----------------|-----------------------|-----------|-----------|-----------| | River Thames | +4 33 | -2 40 | +4 8 | -6 6 | | Portland | +4 38 | -3 8 | +4 53 | -6 37 | Indication of rapid changes in the ship’s magnetism was also given by the ship’s established standard compass, which had been compensated on the passage down the river Thames (from the known direction of the ship’s head by astronomical bearings), and deemed by the gentlemen engaged for the purpose as correct. At Portland, with head in the N.W. direction, it had $7^\circ$ error on the second day at that anchorage. * Communicated in a letter to Mr. Rundell, Secretary of the Liverpool Compass Committee. This error, as also a smaller one considered to exist after the ship's arrival at Holyhead, was, as I understood, eliminated prior to my visit at that port in the latter part of October; but on then determining the deviations of the Admiralty Standard compass, and referring the results to the ship's compensated standard, a residual error in the latter of nearly 5° still existed on some of its points. [Although the question of compensation is extraneous to the general tenor of this Report, I deem it of interest to record the above circumstances, to correct a misapprehension as to the employment of long needles, carried, in the compasses of the Great Eastern, to the extent of 11 inches for standard and steering, and 16 inches for the mast-compass. A series of experiments, still in progress, which I have instituted in elucidation of the comparative errors due to the use of long and short needles, both where the disturbing cause is comparatively close to the compass, as in the case of the rudder-head near the steering compass, or the top sides and iron beams when heeling, and in compensated compasses from the necessary proximity of bar magnets, lead to the conclusion that no compass-needle should exceed in length, for service in an iron ship, 6 or 7 inches; the card of course may be enlarged as practically convenient. The errors of long needles, under the conditions just named, of proximity to permanent magnetic bodies, arise from this notable fact, that their deviations assume the form, not of a curve which is simply "semicircular," as the curve is found to be which results from the ship's general magnetic force when the length of the needle may be relatively considered as infinitesimally small, but of a "sextantal" superposed on a "semicircular" curve, the various maxima of the "sextantal" curve increasing with the square of the length of the needle. Assuming the zero of both curves (the semicircular and sextantal) to be at the magnetic North and South, the maxima of the sextantal deviations (by ship's compass) are respectively at about N. 30° E., East, S. 30° E., S. 30° W., West, N 30° W., the points of coincidence with the semicircular curve being at North, N. 60° E., S. 60° E., South, S. 60° W., and N. 60° W.] The tendency of the direction of the ship's force in the Great Eastern is to assume a fore-and-aft line, supporting the view, that time, with the vibrations and concussions due to sea-service, leads to a settled distribution of the magnetic lines; the respective sections of the hull which have north and south polarity being separated by lines approximating more nearly to a horizontal equatorial plane through the body of the ship, instead of the inclined equatorial plane of separation due to the magnetic dip of the locality, and divergence from the magnetic meridian of the hull while building. A similar tendency of the direction of the ship's force to approach a fore-and-aft line will be observed in several examples of Table I. The example of the Great Eastern offers this practical information; that prior to a newly built iron ship being sent to sea, her head (while being equipped) should be secured in an opposite direction to that in which she was built; and that the magnetic lines should be assisted to be "shaken down" by the vibrations of the machinery in a short preparatory trip prior to the determination of her compass errors, or their com- pensation; but especially that on the early voyages vigilant supervision should be exercised in the determination of the compass disturbances. Another important point, which is generally neglected when compasses are adjusted by the aid of magnets in a newly built iron ship, is rendered manifest from the circumstances just detailed, namely, the necessity of the errors of the compass arising from the iron in a ship being determined and placed on record prior to its adjustment. Without the knowledge, to be derived from these observations, of the magnetic force of the ship, or the local disturbing cause (if such exists), all future changes of magnetism, and consequent errors of the compass, are the merest guesswork, both to those who adjust and the authorities in charge of the navigation of the ship. Any future legislation for the security of the navigation of our mercantile marine with reference to iron-built ships, should secure the determination and record of these preliminary observations. I have alluded to the importance of the conclusions to be derived from a review of the examples and cases given in this Report; for although varying conditions of compass disturbance exist, and the inference is irresistible that they arise from the nature of the iron employed in the construction of the hull of the ship, there is no doubt that, by attention to a few leading principles in the building and equipment of iron ships, the larger and uncertain sources of error may be modified and reduced within limits both of fluctuation and amount, that will not seriously compromise the safety of the ship in the hands of an ordinarily prudent seaman. The points of practical import to which I would invite attention are,— 1st. The best direction, with reference to the magnetic meridian, for the keel and head of an iron ship to be placed for building, to ensure the least compass disturbance. 2nd. The best position and arrangement for a compass, to ensure small deviations, and permanency on changes of geographic position. 3rd. The changes to which the compass is liable from various causes when the foregoing conditions are fulfilled. Before entering on these points, I would refer to an appended series of diagrams (Plate XVI.) illustrative of the polarity of the topsides (and the coefficients B and C), according to the direction of the build; these diagrams forming the key to much that comes under review. 1. On the best Direction for Building an Iron Ship. In those built head N.E., East, West, and N.W., strong south polarity (or an attractive force on the north end of the compass needle) obtains on one side of the ship adjoining the compass as usually placed between the middle section and the stern; the resulting disturbance is not lessened as the compass is moved in a fore-and-aft line within these limits. In vessels built head S.E. and S.W., north polarity obtains under the same conditions. In vessels built head North or South, the conditions arise, that in the former the attraction is toward the stern (the topsides in their action being neutral to a compass in the middle line of the deck), and diminishes in force as the compass is moved towards the bow. In the latter the law is reversed, and small compass deviations are obtained as the stern is approached. In an iron sailing ship, built head to South, there will be an attraction of the north point of the compass to the head, and if built head to North, a like attraction to the ship's stern; and so far there would seem to be no advantage in one direction over the other. But in the first case the topsides near the compass have weak magnetism; in the second case they are strongly magnetic: the first position seems therefore preferable. In an iron steam-ship, built head to the South, the attraction due to machinery is added to that of the hull, whereas in one built head to the North, the attractive forces of hull and machinery are, in the northern hemisphere, antagonistic, and a position of small, or no "semicircular" deviation for the compass may generally be obtained. To iron steam-vessels engaged on the home or foreign trades in the northern hemisphere, this direction of build is therefore to be preferred. 2. On the Position and Arrangements for the Compass. The position of compasses, whether standard or steering, must depend, as will have been observed from the foregoing conclusions, on the direction of the ship's build; that is, in those built head North the compass must be as far removed from the stern as circumstances will permit; in those built South, placed as near to the stern as convenient, without approaching so close to the rudder-head or iron taffrail as to cause the ship's general magnetism to be overpowered by the magnetic influence of those masses. In ships built East or West there is little choice of position, except to avoid, as a general rule, proximity to vertical masses of iron; in vessels built with their heads on the intercardinal points, a position approximating to the bow or stern respectively, where the action from the topsides (to be determined experimentally) is at a minimum, is to be preferred. Ample elevation above the deck, and to be strictly confined to the middle line of the ship, are the primary conditions of position for every compass in an iron ship, and no compass, whether steering or standard, should be nearer the iron deck beams than 4 feet*: for the steering compass this arrangement could be met by the use of a vertical card for the helmsman. The standard compass, which as a rule I should recommend to be invariably uncompensated, requires an elevation of at least 5 or 6 feet from the deck, and to be fitted on * A curious illustration of the effect of iron deck beams on long and short compass-needles resulted from some experiments made on board H.M.S. Bloodhound: on the deck, or within a few inches of the position where, not unfrequently, hanging or tell-tale compasses are placed, a 10-inch needle had $43^\circ$, a 6-inch needle $38^\circ$, and a $1\frac{1}{2}$-inch needle $38^\circ$ difference from their uniform deviation at 1 foot 9 inches from the deck. a separate and permanent pillar or stand: it is by this superior elevation that the strong magnetic power of the iron beams and adjoining topsides are correspondingly lessened. As every piece of iron not composing a part of, and hammered in the fabrication of the hull,—such as the rudder, funnel, boilers and machinery, tanks, cooking galleys, fastenings of deck houses, &c.,—are all of a magnetic character differing from the hull of a ship, their proximity should be avoided, and, so far as possible, the compass should be placed so that they may act as correctors of the general magnetism of the hull. A compass placed out of the middle line of the deck is affected by the nearest topside, and its deviations must necessarily be much increased if that topside has the dominant polarity, as in ships built East or West. Experience has proved that the practical value of mast or elevated compasses has in some cases been overrated; they are, in fact, affected by the ship’s magnetism to an amount depending on their elevation and the direction of the ship’s build: thus in ships built North or South, but especially the latter—the compass being on the mizen mast—the deviations will be large comparatively. In ships built East or West the deviations will be comparatively small, from the topside, which would affect a deck compass, being more directly under the mast-compass; they may therefore be useful in the latter cases, and valueless in a ship built head to the South. The wear and tear on the pivots and agate caps of mast-compasses, from the increased motion due to their elevation, require constant attention when they are employed. 3. On various Sources of Error affecting a Compass placed under favourable conditions. Errors arising from changes of geographic position, as also incidental causes of error due to anomalous rather than general conditions, have been brought under review in the general progress of this Report. There is, however, one source of compass-error—that arising from the heeling of the ship—which has not been alluded to, as the ship in all the points hitherto reviewed is assumed to be on an even keel. The few experiments made in ships of the Royal Navy will be found in Table I., and they tend to prove, as also does the test of experience, that when the original compass deviations are small, the errors from heeling are generally small in proportion; and conversely, that exaggerated errors from heeling are the consequence of exaggerated errors while on an even keel. Ample elevation from the deck, in order to raise the compass above the level of the topsides and adjacent deck beams, is one of the chief conditions for reducing this source of error. The action of the topside nearest to the compass when the ship is heeled is well marked in the examples of the ships Bloodhound and Sharpshooter, the former with \(+B\), or head built to South, and the latter with \(-B\), or head built to North; in the Bloodhound the north end of the needle is drawn to leeward, in the Sharpshooter to windward. In the iron sailing-brig Recruit, with \(+B\), the effect is the same as in the Bloodhound. From the diagrams illustrative of the polarity of an iron ship’s topsides, the action of the latter on the compass in heeling may be gathered, and the corresponding effect shown, under the various directions of the ship's head in building: thus— With head built North, on heeling, the north end of compass needle will be attracted to the weather or nearest side from its south polarity. " N.E., " " the same. " East, " " the same. " S.E., " " the north end of needle will have but little error from the balanced conditions of north and south polarity of topsides. " South, " " the north end of needle will be repelled to the lee side by the north polarity of nearest or weather topside. " S.W., " " the north end of needle will have but little error, as at S.E. " West, " " the north end of needle will be attracted to the weather or nearest side. " N.W., " " the same.* These laws only hold good as long as the topsides in the immediate vicinity of the compass retain their dominant polarity due to their original direction of build in Great Britain: if in south magnetic latitudes a change of polarity takes place, the conditions of heeling correspond to such change. The maximum disturbance on heeling in all these vessels is when their heads are (by disturbed compass) magnetic North or South, and this disturbance vanishes when the head is East or West. This law of disturbance may be thus explained: when the vessel's head is north or south on an even keel (by disturbed compass), the needle lies parallel to the topsides by their combined action, which neutralizes each other; on heeling, the nearest topside exercises its then dominant polarity at right angles to the direction of the needle, and hence the maximum error. With the ship's head east or west, whether on an even keel or heeling, either pole of the compass-needle points directly to the topsides, and is consequently unaffected except in a vertical plane. As the amount of disturbance on heeling varies under the various conditions of direction of build, height of compass, and breadth of ship or distance of topsides, added to the prevailing permanent or inductive magnetic condition of the latter and the deck beams, each ship must have an individual character, to be determined only by experiment or observation at sea. There are, however, strong grounds for inferring that by a * These principles have in their main features been confirmed by the experiments and investigations of the Secretary of the Liverpool Compass Committee,—Mr. Rundell,—to whom I am indebted for much valuable information on many questions of theoretical and practical value; but their simple illustration by a consideration of the appended diagrams, which, so far as I am aware, are novel in their application, will probably be found instructive and useful to the practical seaman. judicious position of the compass, so as to ensure small errors while on an even keel, the errors arising from the ship's heel will be so proportionally reduced, as not practically to affect the navigation of the ship in the hands of a prudent seaman. In concluding this Report, which in some of its details will, I trust, be found to narrow the grounds of inquiry in this interesting branch of science, so important in its practical relations to a maritime nation rapidly expanding its iron commercial navy, I beg leave to record the material assistance I have derived from the researches of the Astronomer Royal and Archibald Smith, Esq., on the subject of a ship's magnetism. Without their skilful analysis and mathematical demonstrations, and much personal assistance rendered by the latter gentleman, I could not have approached the subject, and can therefore claim but little merit,—except that due to the labours of a lengthened computation, and some practical experience and close observation,—in the elucidation of whatever principles may be received as sound in practice and as additions to science. I have the honour to be, Sir, Your obedient Servant, FREDK. J. EVANS, Master R.N. To Captain Washington, R.N., F.R.S., Hydrographer to the Admiralty. APPENDIX. No. I. The Admiralty Standard Compass. The chief points in the construction of this instrument are the following: 1. The bowl is constructed of stout copper with the view to calm the vibrations of the needle, and the intersecting point of the axis of its gimbals is made to coincide with the point of suspension of the card, and also with the centre of the azimuth circle. 2. The azimuth circle is accurately graduated to minutes of arc, and may be used in addition on shore for surveying purposes: thus when accurate magnetic bearings are required, the zero of the circle may be adjusted to the magnetic north, shown by the card, and then clamped; any number of magnetic bearings may then be obtained round the circle: or by adjusting the zero of the circle to any given object and clamping the compass to its stand, the angles of objects round the horizon may be observed and read off to the nearest minute. In observing Amplitudes and Azimuths, the bearings are read from the card without reference to the azimuth circle, the card being graduated to 20 minutes. 3. The magnetic needles employed are compound bars, formed of laminae of that kind of steel (clock-spring) which has been ascertained by numerous experiments to be capable of receiving the greatest magnetic power. Each compass has two cards, A and J; the former is used at all times, except in stormy weather with much motion in the ship, when the heavy or J card is substituted. Each card is fitted with four needles fixed vertically and equidistant on a light framework of brass screwed to the card; the pair of central needles are 7·3 inches long, and the pair of external ones 5·3 inches, the whole weight of the A card being 1525 grains*. The pivots for the needles are pointed with "native alloy," as being harder than steel, and not subject to corrosion by exposure to the atmosphere; the ruby cap of the card is worked to a form to suit these points. 4. The impressions of the cards are taken after the paper has been cemented to the mica plate forming the basis; distortions from shrinking are thus prevented and a more perfect centering attained. Finally. The cards and needles are adjusted to the magnetic meridian at the Compass Observatory for Her Majesty's Navy at Woolwich, a place free from the local influence of iron. The various adjustments for centering, and the elimination of errors * In order that a vibration communicated to a card about a diameter intermediate between the N. and S., and the E. and W. diameters, may not give rise to a "wabbling" motion, the moment of inertia of the card about these two diameters should be the same. It was shown by Mr. Archibald Smith that this is the case with any two parallel needles of uniform thickness forming chords of the same circle, if their extremities are separated by 60°; consequently, with any four such needles, if their extremities are separated by 30°; and the needles of the Admiralty Standard compasses have been uniformly so arranged. due to displacement of sight-vanes, and prism, are also made at this observatory, the compass being afterwards supplied to Her Majesty's ships perfectly free from error. No. II. Table of Magnetic Elements (Terrestrial). | Place | Inclination, or Dip. | Total Intensity, in 1840. | Horizontal intensity. | |--------------------------------------------|----------------------|--------------------------|-----------------------| | From Magnetic Survey of the British Islands | | | | | Greenwich | +69 17 | 1837 | 1-372 | | Greenhithe | +69 15 | 1859 | +68 25 | | Sheerness | +69 12 | | 1-370 | | Portsmouth | +69 2 | | 1-369 | | Portland | +69 7 | | 1-372 | | Plymouth | +69 16 | | 1-375 | | Holyhead | +70 52 | | 1-395 | | River Tagus | +64 0 | 1840a | +60 39 f | | Malta | +52 0 | | 1-35 | | Corfu | +55 0 | 1857 | +55 42 g | | Athens | +51 0 | | 1-21 | | Constantinople | +54 0 | | 1-20 | | River Danube, St. George's Mouth | +60 0 | | 1-22 | | Madeira | +60 30 | 1847 | +59 42 | | St. Vincent, Cape de Verd Islands | +45 0 | | 1-34 | | River Gambit | +38 30 | | 1-15 | | Isles de Los | +33 30 | | 1-11 | | Fernando Po | 0 0 | | 0-95 | | Ascension Island | +0 30 | | 0-90 | | Tristan d'Acunha | -43 0 | | 0-90 | | Cape of Good Hope | -53 20 | 1857 | -54 42 h | | St. Paul's (Indian Ocean) | -68 0 | | 1-98 | | Kurrahee | +28 15 | | 1-50 | | Hong Kong | +30 20 | 1858 | +31 26 h | | Canton | +31 30 | | 1-16 | | Shanghai | +44 0 | 1857 | +45 18 h | | Apia, Upolu I. (Pacific Ocean) | -35 30 | | 1-30 | | Sydney, New South Wales | -62 45 | 1849 | -62 45 | | Port Nicholson, New Zealand | -65 0 | 1850 | -64 52 | | King George's Sound | -65 0 | 1845 | -65 12 | | Swan River, Australia | -62 30 | 1846 | -63 6 | | Sydney, Cape Breton Island | +70 30 | | 1-67 | | St. John's, Newfoundland | +0 0 | | 1-66 | | Halifax, Nova Scotia | +73 45 | 1847 | +75 37 | | Penetanguishine, Lake Huron | +76 0 | 1844 | +76 20 | | Antigua | +50 0 | | 1-67 | | Rio de Janeiro | -12 30 | 1857 | -11 21 h | | Monte Video | -35 0 | 1853 | -32 7 i | | Callao | -7 0 | | 1-06 | | Valparaiso | -38 30 | 1857 | -35 37 k | | Sandwich Islands, Honolulu | +40 30 | 1857 | +42 0 k | | Vancouver Island, Esquimalt | +72 0 | 1858 | +71 55 k | | Nanaimo | +72 20 | | 1-70 | Notes: a) On the authority of General Sabine, from Keith Johnston's Physical Atlas, Second Edition, "Terrestrial Magnetism." b) Computed from the formula $X = R \cos \theta$, in which $R$ denotes the total intensity, $X$ its horizontal component, and $\theta$ the dip. c) Philosophical Transactions for 1856, Mr. Airy "On the Observed Deviations of the Compass in Wood-built and Iron-built Ships." d) From the Atlas des Erdmagnetismus of Gauss. Leipzig, 1840. e) Dr. J. Lamont, "Erdmagnetismus an verschiedenen Punkten des Südwestlichen Europa." Munich, 1858. f) Dr. F. Schaub, "Magnetische Beobachtungen im Östlichen Theile des Mittelmeeres." Trieste, 1858. g) From Captain Shadwell, R.N., Her Majesty's Ship Highflyer. h) From Lieutenant Gilliss, United States Navy. i) From Captain G. H. Richards, R.N., Her Majesty's Surveying Ship Plumper. ### Table I.—Iron-built Ships, Her Majesty's Navy. | Date | Place of observation | Ship's name and Tonnage | Permanent coefficients | Coefficient | Ship's force to Head, Earth's horizontal force = 1000. | Coefficient | Ship's force to Starboard, Earth's horizontal force = 1000. | |---------------|----------------------|-------------------------|------------------------|------------|-----------------------------------------------------|------------|----------------------------------------------------------| | Feb. 25, 1855.| Portsmouth | Himalaya, 3453 | +0.46 | +3.51 | -0.2751 | -0.33 | -0.0096 | | Nov. 21, 1856.| Plymouth | | +0.30 | +2.48 | -0.2428 | -0.23 | -0.0067 | | July 4, 1859. | Plymouth | | +0.20 | +3.18 | -0.2433 | +2.53 | -0.0503 | | Sept. 21, 1855.| Sheerness | Urgent, 1981 | +0.4 | +2.58 | -0.2136 | +0.58 | -0.0169 | | Nov. 7, 1855. | Malta | | +0.54 | +3.6 | -0.1247 | -0.31 | -0.0090 | | June 25, 1856.| Plymouth | | -0.20 | +2.45 | -0.1802 | +1.51 | -0.0323 | | Oct. 29, 1857.| Portsmouth | Urgent | +0.32 | +2.22 | -0.1515 | +3.34 | -0.0622 | | Oct. 11, 1859.| Portsmouth | | +0.38 | +2.12 | -0.1484 | +1.37 | -0.0282 | | Feb. 19, 1852.| Portsmouth | SDOOM* | +0.11 | +3.57 | +0.3434 | -7.15 | -0.1262 | | Sept. 28, 1852.| Portsmouth | | -0.9 | +4.33 | +0.3439 | -7.18 | -0.1271 | | Feb. 1853. | Cape of Good Hope | | -1.47 | +4.13 | +0.2266 | -2.23 | -0.0416 | | Jan. 13, 1857.| Portsmouth | | -0.6 | +3.50 | +0.3231 | -1.35 | -0.0276 | | Nov. 5, 1859. | Portsmouth | | +0.23 | +3.25 | +0.3154 | +1.14 | -0.0215 | | June 14, 1855.| Portsmouth | Perseverance, 1967 | +0.4 | +3.18 | -0.1158 | +1.33 | -0.0270 | | Mar. 13, 1856.| Portsmouth | | +0.52 | +2.53 | -0.1311 | +1.45 | -0.0305 | | Aug. 10, 1858.| Portsmouth | | +0.10 | +1.51 | -0.0926 | +0.10 | -0.0029 | | Oct. 8, 1859. | Portsmouth | | +0.30 | +2.0 | -0.0886 | +2.25 | -0.0422 | | Aug. 31, 1855.| Greenhithe | Transit, 2587 | -0.12 | +3.12 | +0.2363 | +0.13 | -0.0038 | | Mar. 17, 1857.| Portsmouth | | -0.44 | +3.12 | +0.1871 | +2.49 | -0.0491 | | May 4, 1857. | Portsmouth | Assistance, 1820 | -0.8 | +3.35 | -0.2249 | +11.49 | -0.2048 | | May 11, 1857. | Portsmouth | | +0.12 | +3.36 | -0.1645 | +11.29 | -0.1991 | | Feb. 24, 1858.| Canton River, China | | +0.23 | +3.24 | -0.0660 | +6.42 | -0.1167 | | May 9, 1857. | Portsmouth | Adventure, 1794 | -0.45 | +3.40 | -0.1714 | +14.38 | -0.2526 | | 1858. | Whampoa, China | | -0.20 | +3.0 | -0.0697 | +7.38 | -0.1328 | | Feb. 21, 1851.| Sheerness | Vulcan, 1764 | +0.38 | +3.20 | -0.1607 | +1.55 | -0.0334 | | Sept. 30, 1851.| Portsmouth | | +0.29 | +3.0 | -0.1498 | +2.12 | -0.0384 | | July 1, 1852. | Portsmouth | | +0.15 | +3.0 | -0.1636 | +2.18 | -0.0401 | | Nov. 19, 1852.| Sydney, New South Wales | F.D. | -0.16 | +2.3 | -0.2360 | +2.43 | -0.0474 | | Feb. 1853. | Cape of Good Hope | | +1.8 | +4.15 | -0.2765 | +1.19 | -0.0230 | | May 26, 1853. | Portsmouth | | +0.31 | +3.5 | -0.1472 | +3.11 | -0.0555 | | June 19, 1854.| Portsmouth | | +0.16 | +3.29 | -0.0291 | +3.6 | -0.0541 | * Head built S. 30° W. magnetic. Keel at an angle of 2° 15' from horizontal plane. † Standard compass changed in its elevation from deck 1 foot 11 inches; diminishing ship's force one-seventh. ‡ F.U. Funnel up. F.D. Funnel down. ### Table I.—Iron-built Ships, Her Majesty's Navy. | Direction | Amount | Resultant of B and C, or ship's Total force. | Magnetic elements | Position of standard compass | Beams | Horse-power and engines | Where built | Date of launching | |-----------|--------|---------------------------------------------|-------------------|-------------------------------|-------|-------------------------|------------|------------------| | | | | Horizontal force. | Dip. and nat. tang. | From funnel | From taffrail | Height from deck. | | | | 182 | 0·275 | 1·000 +68 25 2·53 | | | ft. in. | ft. in. | ft. in. | Iron. | 700, Screw. | Blackwall. | 1854. | | 181½ | 0·243 | 1·000 +68 25 2·53 | | | 113 0 | 62 0 | 8 4 | | | | | | 168½ | 0·248 | 1·000 +68 25 2·53 | | | 113 0 | 62 0 | 8 4 | | | | | | 175½ | 0·215 | 1·000 +68 25 2·53 | | | 91 0 | 72 0 | 5 0 | Poop-deck, wood. | 450, Screw. | Blackwall (Mare and Co.). | 3rd April, 1855. | | 184 | 0·125 | 1·510 +52 0 1·28 | | | 91 0 | 72 0 | 5 0 | | | | | | 170 | 0·183 | 1·000 +68 25 2·53 | | | 91 0 | 72 0 | 5 0 | | | | | | 157½ | 0·163 | 1·000 +68 25 2·53 | | | 91 0 | 72 0 | 5 0 | | | | | | 169½ | 0·151 | 1·000 +68 25 2·53 | | | 91 0 | 72 0 | 5 0 | | | | | | 340 | 0·367 | 1·000 +68 25 2·53 | | | 55 4 | 33 10 | 4 2½ | Poop-deck, wood. | 350, Screw. | Glasgow (R. Napier). | 24th May, 1849. | | 340 | 0·367 | 1·000 +68 25 2·53 | | | 55 4 | 33 10 | 4 2½ | | | | | | 350 | 0·215 | 1·174 -54 42 -1·41 | | | 55 4 | 33 10 | 4 2½ | | | | | | 355 | 0·326 | 1·000 +68 25 2·53 | | | 55 4 | 33 10 | 4 2½ | | | | | | 4 | 0·316 | 1·000 +68 25 2·53 | | | 56 4 | 31 6 | 4 6 | | | | | | 167 | 0·119 | 1·000 +68 25 2·53 | | | 97 0 | 71 0 | 4 3 | Poop-deck, wood. | 350, Screw. | Blackwall (Mare and Co.). | 13th July, 1854. | | 167 | 0·134 | 1·000 +68 25 2·53 | | | 97 0 | 71 0 | 4 3 | | | | | | 178 | 0·093 | 1·000 +68 25 2·53 | | | 88 0 | 67 0 | 5 4 | | | | | | 154½ | 0·098 | 1·000 +68 25 2·53 | | | 88 0 | 67 0 | 5 4 | | | | | | 1 | 0·236 | 1·000 +68 25 2·53 | | | 105 0 | 72 0 | 4 6 | Poop-deck, wood. | 500, Screw. | Blackwall (Mare and Co.). | 20th Mar. 1855. | | 15 | 0·194 | 1·000 +68 25 2·53 | | | 105 0 | 72 0 | 4 6 | | | | | | 138 | 0·304 | 1·000 +68 25 2·53 | | | 122 0 | 30 0 | 4 5 | Iron. | 400, Screw. | Birkenhead (Laird). | 5th April, 1855. | | 130 | 0·259 | 1·000 +68 25 2·53 | | | 122 0 | 30 0 | 6 4 | | | | | | 120 | 0·134 | 2·049 +32 35 0·63 | | | 122 0 | 30 0 | 6 4 | | | | | | 124 | 0·305 | 1·000 +68 25 2·53 | | | 125 0 | 30 0 | 6 4 | Iron. | 400, Screw. | Birkenhead (Laird). | 17th Feb. 1855. | | 118 | 0·150 | 2·049 +31 30 0·61 | | | 125 0 | 30 0 | 6 4 | | | | | | 168½ | 0·163 | 1·000 +68 30 2·54 | | | 27 10 | 49 8 | 5 0 | Poop-deck, wood. | 350, Screw. | Blackwall (Ditchburn and Mare). | 27th Jan. 1849. | | 166 | 0·154 | 1·000 +68 30 2·54 | | | 27 10 | 49 8 | 5 0 | | | | | | 166½ | 0·168 | 1·000 +68 30 2·54 | | | 27 10 | 49 8 | 5 0 | | | | | | 175½ | 0·153 | 1·000 +68 30 2·54 | | | 27 10 | 49 8 | 5 0 | | | | | | 168½ | 0·241 | 1·506 -62 45 -1·94 | | | 27 10 | 49 8 | 5 0 | | | | | | 175 | 0·278 | 1·174 -54 42 -1·41 | | | 27 10 | 49 8 | 5 0 | | | | | | 160 | 0·157 | 1·000 +68 30 2·54 | | | 27 10 | 49 8 | 5 0 | | | | | | 118 | 0·062 | 1·000 +68 30 2·54 | | | 27 10 | 49 8 | 5 0 | | | | | MDCCCLX. ### Table I.—Iron-built Ships, Her Majesty's Navy (continued). | Date | Place of observation | Ship's name and tonnage | Permanent coefficients | Coefficient | Ship's force to North Pole, Earth's horizontal force =1'000. | Coefficient | Ship's force to South Pole, Earth's horizontal force =1'000. | |---------------|----------------------|-------------------------|------------------------|-------------|----------------------------------------------------------|-------------|----------------------------------------------------------| | Apr. 17, 1856 | Portsmouth | VULCAN, 1764 | -0° 9′ +3° 7′ -0° 3′ -7° 37′ | -0.1325 | +3° 33′ | 0.0619 | | Nov. 6, 1856 | Sheerness | continued | F.D. +0° 27′ +1° 55′ +0° 21′ -5° 4′ | -0.0883 | +3° 50′ | 0.0668 | | Sept. 4, 1857 | Portsmouth | F.U. +0° 30′ +2° 56′ -0° 3′ -1° 58′ | -0.0343 | +4° 58′ | 0.0866 | | | | F.D. +0° 13′ +2° 55′ -0° 16′ +0° 51′ | 0.0148 | +5° 11′ | 0.0903 | | Aug. 16, 1859 | Portsmouth | F.U. +0° 40′ +2° 48′ +0° 28′ -4° 20′ | -0.0756 | +9° 37′ | 0.1670 | | | | F.D. +0° 36′ +2° 51′ +0° 5′ -1° 34′ | -0.0273 | +9° 25′ | 0.1636 | | Oct. 22, 1851 | Sheerness | MEGERA, 1395 | F.D. -0° 15′ +1° 46′ +0° 32′ -12° 43′ | -0.2201 | -2° 5′ | 0.0363 | | | | | F.U. +0° 3′ +2° 32′ -0° 8′ -13° 5′ | -0.2264 | -3° 12′ | 0.0558 | | Sept. 11, 1852| Sheerness | | -0° 24′ +1° 15′ +0° 29′ -11° 52′ | -0.2056 | +6° 52′ | 0.1196 | | Dec. 8, 1853 | Antigua | | +0° 5′ +1° 36′ -0° 5′ -5° 46′ | -0.1005 | +3° 58′ | 0.0692 | | Jan. 23, 1857 | Portsmouth | | +0° 46′ +1° 48′ -0° 23′ -12° 1′ | -0.2082 | +3° 51′ | 0.0671 | | Jan. 20, 1847 | Greenhithe | BIRKENHEAD, 1405 | +0° 18′ +2° 53′ -0° 11′ -13° 51′ | -0.2394 | -6° 27′ | 0.1123 | | Feb. 19, 1847 | Portsmouth | | -0° 14′ +2° 44′ +0° 25′ -13° 51′ | -0.2394 | -6° 39′ | 0.1158 | | Mar. 20, 1848 | Portsmouth | | -0° 29′ +2° 48′ +0° 23′ -13° 30′ | -0.2334 | -6° 32′ | 0.1138 | | | | | -0° 30′ +2° 13′ +0° 22′ -13° 36′ | -0.2351 | -6° 54′ | 0.1201 | | Feb. 17, 1851 | Portsmouth | | -0° 33′ +2° 12′ +0° 27′ -13° 51′ | -0.2394 | -6° 48′ | 0.1184 | | Aug. 10, 1846 | Greenhithe | TRIDENT, 850 | +0° 88′ +4° 3′ +0° 45′ +20° 8′ | 0.3442 | +1° 13′ | 0.0212 | | | | | +0° 25′ +3° 46′ +0° 30′ +13° 38′ | 0.2357 | -2° 0′ | -0.0349 | | May 23, 1848 | Greenhithe | | +0° 37′ +3° 52′ +0° 21′ +21° 1′ | 0.3586 | -0° 13′ | -0.0088 | | Oct. 17, 1849 | Plymouth | | +0° 25′ +3° 31′ -0° 6′ +18° 26′ | 0.3162 | -0° 2′ | -0.0006 | | Sept. 8, 1852 | Greenhithe | | +0° 5′ +3° 38′ +0° 27′ +19° 41′ | 0.3368 | -2° 37′ | -0.0456 | | Nov. 7, 1852 | Rio Janeiro | | -0° 10′ +4° 3′ -0° 9′ +12° 18′ | 0.2130 | -1° 52′ | -0.0326 | | Dec. 23, 1856 | Greenhithe | | -0° 11′ +3° 43′ +0° 10′ +21° 50′ | 0.3719 | -3° 26′ | -0.0599 | | May 1857 | Ascension Island | | +1° 3′ +2° 50′ +1° 21′ +12° 15′ | 0.2122 | -4° 2′ | -0.0703 | | November 1857 | Cape of Good Hope | | -0° 22′ +2° 55′ -0° 6′ +16° 27′ | 0.2832 | -1° 35′ | -0.0276 | | Oct. 31, 1859 | Greenhithe | | -0° 8′ +3° 26′ +0° 34′ +18° 40′ | 0.3201 | +0° 50′ | 0.0145 | | Nov. 19, 1855 | Greenhithe | HESPER, 808 | +1° 13′ +3° 10′ +0° 36′ -0° 7′ | -0.0020 | -3° 17′ | -0.0573 | | Oct. 11, 1856 | Greenhithe | | +0° 12′ +3° 0′ +0° 38′ +1° 28′ | 0.0256 | -0° 27′ | -0.0078 | | May 1, 1857 | Greenhithe | | +0° 12′ +3° 17′ +0° 21′ +2° 22′ | 0.0413 | +0° 23′ | 0.0067 | | June 8, 1848 | Greenhithe | CARADOC, 676 | +0° 43′ +3° 13′ +0° 18′ -12° 33′ | -0.2173 | -4° 15′ | -0.0741 | | May 21, 1852 | Malta | | +0° 31′ +2° 15′ -0° 17′ -9° 42′ | -0.1685 | -1° 33′ | -0.0270 | | Nov. 4, 1855 | Greenhithe | | -0° 25′ +2° 6′ +0° 12′ -10° 54′ | -0.1891 | -2° 8′ | -0.0372 | ### Table I.—Iron-built Ships, Her Majesty's Navy (continued). | Direction | Amount | Resultant of B and C, or ship's total force. | Magnetic elements | Position of standard compass | Beams | Horse-power and engines | Where built | Date of launching | |-----------|--------|---------------------------------------------|-------------------|-------------------------------|-------|-------------------------|------------|------------------| | | | | Dip, and nat. tang. | From funnel. | From tafrail. | Height from deck. | | | | 155 | 0-146 | 1-000 +68 30 2-54 | ft. in. ft. in. ft. in. | 26 4 | 49 8 | 5 2 | Wood, on poop-deck. | 350, Screw. | Blackwall (Ditchburn and Mare). | 27th Jan. 1849. | | 143 | 0-111 | 1-000 +68 30 2-54 | | 26 4 | 49 8 | 5 2 | | | | | 111 | 0-093 | 1-000 +68 30 2-54 | | 26 4 | 49 8 | 5 2 | | | | | 81 | 0-092 | 1-000 +68 30 2-54 | | 26 4 | 49 8 | 5 2 | | | | | 114 | 0-183 | 1-000 +68 30 2-54 | | 26 5 | 50 4 | 5 4 | | | | | 100 | 0-166 | 1-000 +68 30 2-54 | | 26 5 | 50 4 | 5 4 | | | | | 189½ | 0-223 | 1-000 +68 30 2-54 | | 78 4 | 38 0 | 3 9 | Wood, on poop-deck. | 350, Screw. | Millwall (Fairbairn). | 22nd May, 1849. | | 193½ | 0-232 | 1-000 +68 30 2-54 | | 78 4 | 38 0 | 3 9 | | | | | 150 | 0-238 | 1-000 +68 30 2-54 | | 78 4 | 38 0 | 3 9 | | | | | 145 | 0-122 | 1-746 +50 0 1-19 | | 78 4 | 38 0 | 3 9 | | | | | 162 | 0-213 | 1-000 +68 30 2-54 | | 77 0 | 39 0 | 4 0 | | | | | 205 | 0-264 | 1-000 +68 45 2-57 | | 52 0 | 38 0 | 4 1 | Wood, on poop-deck. | 556, Paddle. | Birkenhead (Laird). | 30th Dec. 1845. | | 206 | 0-265 | 1-000 +68 45 2-57 | | 52 0 | 38 0 | 4 1 | | | | | 206 | 0-260 | 1-000 +68 45 2-57 | | 52 0 | 38 0 | 4 1 | | | | | 207 | 0-264 | 1-000 +68 45 2-57 | | 52 0 | 38 0 | 4 1 | | | | | 206 | 0-267 | 1-000 +68 45 2-57 | | 52 0 | 38 0 | 4 1 | | | | | 3 | 0-345 | 1-000 +68 45 2-57 | | 36 6 | 35 0 | 5 0 | Wood, on quarter-deck. | 350, Paddle. | Blackwall (Ditchburn and Mare). | 16th Dec. 1845. | | 35½ | 0-238 | 1-510 +52 0 1-28 | | 36 6 | 35 0 | 5 0 | Iron in fore-part of ship. | | | | 359½ | 0-359 | 1-000 +68 45 2-57 | | 36 6 | 35 0 | 5 0 | | | | | 360 | 0-316 | 1-000 +68 45 2-57 | | 36 6 | 35 0 | 5 0 | | | | | 352½ | 0-342 | 1-000 +68 45 2-57 | | 36 6 | 35 0 | 5 0 | | | | | 351 | 0-216 | 1-708 -11 21 0-20 | | 36 6 | 35 0 | 5 0 | | | | | 351 | 0-376 | 1-000 +68 30 2-54 | | 36 6 | 35 0 | 5 1 | | | | | 341½ | 0-378 | 1-673 +0 30 0-01 | | 36 6 | 35 0 | 5 1 | | | | | 354½ | 0-333 | 1-174 -54 42 1-41 | | 36 6 | 35 0 | 5 1 | | | | | 2½ | 0-320 | 1-000 +68 25 2-53 | | 36 6 | 35 0 | 5 1 | | | | | 272 | 0-057 | 1-000 +68 30 2-54 | | 49 6 | 102 0 | 11 1 | Iron. | 120, Screw. | | | 344 | 0-026 | 1-000 +68 30 2-54 | | 49 6 | 102 0 | 11 1 | | | | | 9 | 0-042 | 1-000 +68 30 2-54 | | 49 6 | 102 0 | 11 1 | | | | | 199 | 0-230 | 1-000 +68 40 2-56 | | 60 0 | 40 0 | 7 0 | Wood. | 350, Paddle. | Blackwall (Ditchburn and Mare). | 3rd July, 1847. | | 189 | 0-171 | 1-511 +52 0 1-28 | | 60 0 | 40 0 | 7 0 | | | | | 191 | 0-193 | 1-000 +68 30 2-54 | | 60 0 | 40 0 | 7 0 | | | | † Compass before the funnel, on bridge. ### Table I.—Iron-built Ships, Her Majesty’s Navy (continued). | Date | Place of observation | Ship’s name and Tonnage | Permanent coefficients | Coefficient | Ship’s force to Head. Earth’s horizontal force =1’000. | Coefficient | Ship’s force to Starboard. Earth’s horizontal force =1’000. | |---------------|----------------------|--------------------------|------------------------|-------------|-----------------------------------------------------|-------------|------------------------------------------------------------| | April 21, 1857 | Malta | CARADOC, 676 | +0°49 | +2°13 | +0°10 | -8°36 | -0°1495 | -1°38 | -0°0285 | | Dec. 13, 1858 | Malta | continued | +1°27 | +2°52 | -0°20 | -8°38 | -0°1501 | -3°6 | -0°0541 | | Sept. 8, 1847 | Greenhithe | ANTELOPE, 650 | +0°14 | +2°58 | +0°10 | -6°42 | -0°1167 | +0°59 | 0°0172 | | Mar. 24, 1852 | Greenhithe | | +0°2 | +2°30 | +0°45 | -6°46 | -0°1178 | -1°1 | -0°0177 | | Sept. 8, 1853 | Portsmouth | | -0°22 | +2°19 | +0°17 | -8°23 | -0°1460 | -3°41 | -0°0642 | | Jan. 8, 1857 | Greenhithe | | +0°29 | +3°4 | +0°23 | -3°8 | -0°0547 | -5°18 | -0°0924 | | Mar. 1, 1848 | Greenhithe | TRITON, 654 | +0°40 | +4°2 | +0°32 | -11°56 | -0°2068 | +0°26 | 0°0076 | | June 23, 1852 | Greenhithe | | -0°3 | +3°8 | +0°23 | -7°47 | -0°1354 | -2°32 | -0°0442 | | Sept. 18, 1832 | Corfu | | +1°10 | +3°20 | -0°2 | -5°36 | -0°0976 | -2°4 | -0°0361 | | Nov. 12, 1857 | Greenhithe | | +0°25 | +2°37 | +0°39 | -8°37 | -0°1498 | -5°34 | -0°0970 | | Dec. 3, 1858 | Fernando Po | | -1°0 | +3°21 | -0°5 | -5°36 | -0°0976 | -0°4 | -0°0012 | | Nov. 16, 1847 | Portsmouth | OBHERON, 649 | +1°35 | +3°23 | +0°13 | +6°18 | 0°1097 | -14°2 | -0°2425 | | July 26, 1851 | Portsmouth | | -0°20 | +2°16 | +0°20 | +5°43 | 0°0996 | -11°57 | -0°2071 | | Nov. 28, 1856 | Malta | | o°o | +2°43 | -0°27 | +3°27 | o°0602 | -6°47 | -0°1181 | | Aug. 10, 1858 | Greenhithe | | -0°5 | +3°27 | +0°8 | +8°15 | 0°1435 | -6°16 | -0°1092 | | Dec. 30, 1858 | Monte Video | | +2°11 | +2°50 | -0°38 | +3°29 | o°0608 | -5°23 | -0°0938 | | July 19, 1854 | Greenhithe | INDUSTRY, 638 | -0°34 | +2°55 | -0°32 | +13°55 | 0°2405 | +3°12 | 0°0558 | | Jan. 10, 1856 | Malta | | -1°10 | +3°0 | -0°23 | +9°9 | o°1590 | -0°9 | -0°0026 | | Sept. 30, 1856 | Greenhithe | | -0°45 | +2°45 | -0°23 | +14°27 | 0°2495 | +3°13 | 0°0561 | | Jan. 13, 1858 | Greenhithe | | +0°26 | +2°31 | +0°22 | +13°17 | 0°2298 | -0°37 | -0°0107 | | Aug. 25, 1858 | Greenhithe | | +0°18 | +2°23 | -0°9 | +10°25 | 0°1808 | -1°11 | -0°0206 | | July 19, 1859 | Greenhithe | | +0°13 | +2°40 | -0°13 | +10°43 | 0°1859 | +0°4 | 0°0011 | | Sept. 4, 1854 | Greenhithe* | SUPPLY, 638 | +0°29 | +3°40 | -0°4 | -16°41 | -0°2871 | +12°2 | 0°2085 | | April 19, 1859 | Greenhithe | | -0°10 | +3°7 | -0°3 | -15°1 | -0°2591 | -0°36 | -0°0105 | | Sept. 19, 1859 | Greenhithe | | -0°35 | +2°23 | -1°20 | -14°3 | -0°2428 | -0°53 | -0°0154 | | Jan. 14, 1860 | Greenhithe | | +0°41 | +2°15 | -0°47 | -15°13 | -0°2625 | -0°5 | -0°0014 | | Mar. 30, 1855 | Plymouth | WESER†, 590 | -0°07 | +3°50 | -0°39 | -11°59 | -0°2076 | +1°16 | 0°0221 | | July 28, 1857 | St. Geo. Mouth, R. Danube | | +0°9 | +4°11 | +0°38 | -6°33 | -0°1141 | -4°47 | -0°0834 | | Nov. 17, 1859 | Greenhithe | | +0°9 | +3°35 | +0°23 | +1°0 | 0°0174 | +3°52 | 0°0674 | | Mar. 29, 1855 | Plymouth | Recruit† (Steam-vessel), 590 | +0°1 | +4°7 | -0°16 | -13°47 | -0°2382 | -0°53 | -0°0154 | * These observations were made with a common prismatic compass; the coefficients have been computed both directly from the observations, and from a probable curve graphically drawn through the observations; the results accord closely. † These vessels were received from the Prussian Government in 1854. ### Table I.—Iron-built Ships, Her Majesty’s Navy (continued). | Direction | Amount | Resultant of B and C, or ship's Total force. | Magnetic elements | Position of standard compass | Beams | Horsepower and engines | Where built | Date of launching | |-----------|--------|---------------------------------------------|-------------------|----------------------------|-------|----------------------|------------|------------------| | | | | Horizontal force. | From funnel. | From taffrail. | Height from deck. | | | | | | | Dip. and nat. tang. | ft. in. | ft. in. | ft. in. | | | | 19° | 0·152 | 1·510 +52° 6' | 60 0 | 40 0 | 7 0 | Wood. | 350, Paddle. | Blackwall (Ditchburn and Mare). | July 3, 1847. | | 200 | 0·229 | 1·510 +52° 0' | 60 0 | 40 0 | 7 0 | | | | | | 0·160 | | 1·28 | | | | | | | | 0·242 | | 1·28 | | | | | | | 171° | 0·118 | 1·000 +68° 40' | 56 0 | 21 0 | 4 7½ | Wood. | 260, Paddle. | Blackwall (Ditchburn and Mare). | July 25, 1846. | | 188° | 0·119 | 1·000 +68° 40' | 56 0 | 21 0 | 4 7½ | | | | | 203° | 0·161 | 1·000 +68° 40' | 56 0 | 21 0 | 4 7½ | | | | | 239 | 0·106 | 1·000 +68° 40' | 37 0 | 41 0 | 4 8 | | | | | 178 | 0·207 | 1·000 +68° 40' | 32 8 | 40 7 | 4 9 | Wood. | 260, Paddle. | Blackwall (Wigram). | Oct. 24, 1846. | | 198 | 0·142 | 1·000 +68° 40' | 32 8 | 40 7 | 4 9 | | | | | 200 | 0·104 | 1·366 +55° 14' | 32 8 | 40 7 | 4 9 | | | | | | 0·142 | | 1·46 | | | | | | | 213 | 0·178 | 1·000 +68° 25' | 35 0 | 36 0 | 4 9 | | | | | 181 | 0·098 | 1·923 0° | 35 0 | 36 0 | 4 9 | | | | | 294 | 0·266 | 1·000 +68° 40' | 52 4 | 21 2 | 4 9½ | Wood. | 260, Paddle. | Deptford (Rennie). | January 2, 1847. | | 295 | 0·230 | 1·000 +68° 40' | 52 4 | 21 2 | 4 9½ | | | | | 297 | 0·133 | 1·510 +52° 0' | 52 4 | 21 2 | 4 9½ | | | | | | 0·201 | | 1·28 | | | | | | | 323 | 0·180 | 1·000 +68° 30' | 41 10 | 30 3 | 4 10 | | | | | 303 | 0·112 | 1·602 -32° 0' | 41 10 | 30 3 | 4 10 | | | | | | 0·179 | | 0·62 | | | | | | | 13 | 0·247 | 1·000 +68° 25' | 73 5 | 18 11 | 4 11 | Iron. | 80, Screw. | Blackwall (Mare and Co.). | 1854. | | 359 | 0·159 | 1·510 +52° 0' | 73 5 | 18 11 | 4 11 | | | | | | 0·240 | | 1·28 | | | | | | | 13 | 0·256 | 1·000 +68° 25' | 73 5 | 18 11 | 4 11 | | | | | 357° | 0·230 | 1·000 +68° 25' | 73 5 | 18 11 | 4 11 | | | | | 353° | 0·182 | 1·000 +68° 25' | 73 5 | 18 11 | 4 11 | | | | | 360° | 0·186 | 1·000 +68° 25' | 73 5 | 18 11 | 4 11 | | | | | 144 | 0·354 | 1·000 +68° 25' | 70 0 | 18 0 | 5 0 | Iron. | 80, Screw. | Blackwall (Mare and Co.). | June 3, 1854. | | 182 | 0·259 | 1·000 +68° 25' | 69 6 | 18 2 | 5 2 | | | | | 183° | 0·243 | 1·000 +68° 25' | 69 6 | 18 2 | 5 2 | | | | | 180° | 0·262 | 1·000 +68° 25' | 69 6 | 18 2 | 5 2 | | | | | 174 | 0·209 | 1·000 +68° 30' | 8 10½ | 66 0 | 11 7 | Wood. | 160, Paddle. | | | 216 | 0·141 | 1·230 +60° 0' | 8 10½ | 66 0 | 11 7 | | | | | | 0·173 | | 1·73 | | | | | | | 75° | 0·069 | 1·000 +68° 25' | 42 4 | 30 0 | 4 6½ | | | | | 184° | 0·239 | 1·000 +68° 25' | 8 10½ | 66 0 | 11 7 | Wood. | 160, Paddle. | | † Compass placed on the bridge, nearly midway between two funnels; the distance is given from the nearest funnel. ### Table I.—Iron-built Ships, Her Majesty's Navy (continued). | Date | Place of observation | Ship's name and Tonnage | Permanent coefficients | Coefficient | Ship's force to Head Earth's horizontal force =1'000. | Coefficient | Ship's force to Starboard Earth's horizontal force =1'000. | |---------------|----------------------|-------------------------|------------------------|------------|-----------------------------------------------------|------------|----------------------------------------------------------| | April 26, 1848 | Portsmouth | SHARPSHOOTER, 503... | A. -0 7 | D. +4 32 | E. +0 14 | B. -7 17 | C. -0 1268 | | | | Heeled 7° to starboard. | | | | | +0 24 | | April 1, 1850 | Portsmouth | | A. +0 16 | D. +3 53 | E. +0 5 | B. -6 1 | C. -0 1048 | | Nov. 12, 1852 | Portsmouth | | A. -0 33 | D. +3 17 | E. -0 21 | B. -16 17 | C. -0 2804 | | Feb. 8, 1853 | Rio de Janeiro | | A. +0 20 | D. +3 2 | E. -0 2 | B. -8 25 | C. -0 1464 | | Dec. 28, 1857 | Portsmouth | | A. +0 10 | D. +4 12 | E. +0 3 | B. -12 44 | C. -0 2204 | | Aug. 31, 1859 | Isles de Los, Africa | | A. -0 45 | D. +3 35 | E. +1 7 | B. -6 58 | C. -0 1213 | | Aug. 28, 1846 | Greenhithe | RECRUIT (Sailing Brig), 462. | A. -0 30 | D. +1 30 | E. -0 33 | B. +3 7 | C. 0 0544 | | Aug. 28, 1846 | Greenhithe | | A. -0 41 | D. +1 7 | E. -1 3 | B. +12 50 | C. 0 2221 | | Nov. 1846 | Plymouth | | A. +2 18 | D. +1 57 | E. -0 8 | B. +12 48 | C. 0 2215 | | | | Heeled 8° to port | | | | | +1 30 | | | | Heeled 8° to starboard. | | | | | +0 21 | | Oct. 18, 1855 | Greenhithe | BARON VON HUMBOLDT, afterwards named | A. -0 18 | D. +5 10 | E. +0 24 | B. +16 33 | C. 0 2848 | | Dec. 15, 1855 | Greenhithe | BUFFALO, 440............ | A. +0 3 | D. +3 4 | E. +0 5 | B. -16 46 | C. -0 2885 | | Dec. 24, 1856 | Greenhithe | | A. +0 2 | D. +3 2 | E. +0 6 | B. -19 6 | C. -0 3272 | | Feb. 26, 1858 | Greenhithe | | A. +0 39 | D. +2 35 | E. +0 23 | B. +13 12 | C. 0 2283 | | Mar. 17, 1846 | Greenhithe | MYRMIDON, 374.......... | A. -0 16 | D. +3 23 | E. +0 3 | B. +15 18 | C. 0 2639 | | Aug. 11, 1851 | Woolwich | | A. +0 46 | D. +3 9 | E. -0 28 | B. +19 23 | C. 0 3319 | | July 2, 1855 | Portsmouth | | A. +0 21 | D. +2 45 | E. +0 12 | B. +17 7 | C. 0 2943 | | Sept. 8, 1855 | Portsmouth | WYE, 700.............. | A. +0 7 | D. +3 24 | E. +0 41 | B. -1 40 | C. -0 0291 | | Sept. 6, 1845 | Plymouth | BLOODHOUND, 378......... | A. +0 23 | D. +3 40 | E. +0 10 | B. +14 37 | C. 0 2523 | | | | CONSTANTINOPLE.......... | A. +0 7 | D. +3 22 | E. -0 51 | B. +10 40 | C. 0 1851 | | | | ATHENS (Piræus)........ | A. +0 25 | D. +3 59 | E. -0 6 | B. +9 0 | C. 0 1564 | | May 11, 1847 | Greenhithe | | A. +0 5 | D. +3 21 | E. +0 4 | B. +11 43 | C. 0 2031 | | | | Heeled 8° to port | | | | | -4 40 | | | | Heeled 8° to starboard. | | | | | +0 32 | | Feb. 12, 1851 | Plymouth | | A. -2 39 | D. +2 35 | E. +0 4 | B. +12 20 | C. 0 2136 | | Sept. 7, 1855 | Greenhithe | | A. +0 13 | D. +2 31 | E. +0 26 | B. +11 46 | C. 0 2039 | | Mar. 20, 1845 | Greenhithe | JACKAL, 340............. | A. -0 25 | D. +4 57 | E. -0 25 | B. +24 7 | C. 0 4086 | | July 16, 1845 | Plymouth | | A. +0 15 | D. +4 13 | E. -0 5 | B. +16 38 | C. 0 2862 | | | | ATHENS (Piræus)........ | A. +0 15 | D. +3 52 | E. -0 7 | B. +10 15 | C. 0 1779 | ### Table I.—Iron-built Ships, Her Majesty's Navy (continued). | Resultant of B and C, or ship's Total force | Magnetic elements | Position of standard compass | Beams | Horse-power and engines | Where built | Date of launching | |--------------------------------------------|-------------------|------------------------------|-------|------------------------|-------------|------------------| | Direction | Amount | Horizontal force | Dip, and nut. tang. | From funnel | From tafrail | Height from deck | Wood | Screw | Blackwall (Ditchburn and Mare) | July 25, 1846 | | 177° | 0-126 | 1-000 | +68 25 | ft. in. | ft. in. | ft. in. | 43 6 | 44 6 | 4 8½ | 202 | Sailing vessel. | Blackwall (Ditchburn and Mare). | 1846. | | 183 | 0-137 | | | | | | 43 6 | 44 6 | 4 8½ | | | | | 180 | 0-105 | 1-000 | +68 25 | | | | 46 0 | 43 0 | 4 8½ | | | | | 180 | 0-280 | 1-000 | +68 25 | | | | 57 4 | 28 11| 5 8 | | | | | 189 | 0°148° | 1-708 | -11 21 | | | | 57 4 | 28 11| 5 8 | | | | | 160 | 0-235 | 1-000 | +68 25 | | | | 57 4 | 28 11| 6 2 | | | | | 172 | 0°122° | 1-821 | +33 30 | | | | 57 4 | 28 11| 6 2 | | | | | 65 | 0-127 | 1-000 | +68 25 | | | | 9 | 2 | | Wood beams. Iron bulwarks. | Blackwall (Ditchburn and Mare). | 1846. | | 22 | 0-240 | 1-000 | +68 25 | | | | 16 | 4 | 1 7† | | | | 7 | 0-223 | | | | | | 16 | 4 | 8 10‡ | | | | 30½ | 0-255 | 1-000 | +68 25 | | | | | | | | | | 46 | 0-349 | | | | | | | | | | | | 339 | 0-302 | 1-000 | +68 25 | | | | 44 | 0 | 12 0 | Iron. | 60, Screw. | Blackwall (Ditchburn and Mare). | February 1845. | | 178 | 0-289 | 1-000 | +68 25 | | | | 6 | 6* | 63 0 | Iron. | 150, Screw. | Blackwall (Ditchburn and Mare). | 9th Jan. 1845. | | 182 | 0-328 | 1-000 | +68 25 | | | | 6 | 6* | 63 0 | Iron. | 150, Paddle. | Glasgow (R. Napier). | 28th Oct. 1844. | | 7 | 0-230 | 1-000 | +68 25 | | | | 34 | 0 | 26 0 | Iron. | Screw. | | | | 11 | 0-269 | 1-000 | +68 30 | | | | 37 | 6 | 23 8 | Iron. | 150, Screw. | Blackwall (Ditchburn and Mare). | 9th Jan. 1845. | | 344 | 0-346 | 1-000 | +68 30 | | | | 37 | 6 | 23 8 | Iron. | 150, Screw. | Blackwall (Ditchburn and Mare). | 9th Jan. 1845. | | 1½ | 0-294 | 1-000 | +68 30 | | | | 37 | 6 | 23 8 | Iron. | 150, Screw. | Blackwall (Ditchburn and Mare). | 9th Jan. 1845. | | 97½ | 0-226 | 1-000 | +68 30 | | | | 51 | 3 | 47 8 | Iron. | Screw. | | | | 351 | 0-256 | 1-000 | +68 40 | | | | 41 | 6 | 14 0 | Iron. | 150, Paddle. | Glasgow (R. Napier). | 28th Oct. 1844. | | 347 | 0-190° | 1-482 | +54 0 | | | | 41 | 6 | 14 0 | Iron. | 150, Paddle. | Glasgow (R. Napier). | 28th Oct. 1844. | | 344 | 0-281 | 1-000 | +68 40 | | | | 41 | 6 | 14 0 | Iron. | 150, Paddle. | Glasgow (R. Napier). | 28th Oct. 1844. | | 338 | 0-249 | 1-000 | +68 40 | | | | 41 | 6 | 14 0 | Iron. | 150, Paddle. | Glasgow (R. Napier). | 28th Oct. 1844. | | 351 | 0-209 | 1-000 | +68 40 | | | | 41 | 6 | 14 0 | Iron. | 150, Paddle. | Glasgow (R. Napier). | 28th Oct. 1844. | | 6 | 0-202 | | | | | | 41 | 6 | 14 0 | Iron. | 150, Paddle. | Glasgow (R. Napier). | 28th Oct. 1844. | | 347 | 0-219 | 1-000 | +68 40 | | | | 42 | 3 | 15 10| Iron. | 150, Paddle. | Glasgow (R. Napier). | 28th Oct. 1844. | | 350 | 0-207 | 1-000 | +68 40 | | | | 42 | 3 | 15 10| Iron. | 150, Paddle. | Glasgow (R. Napier). | 28th Oct. 1844. | | 2 | 0-409 | 1-000 | +68 40 | | | | 25 | 6 | 32 6 | Iron. | 150, Paddle. | Glasgow (R. Napier). | 28th Oct. 1844. | | 353 | 0-288 | 1-000 | +68 40 | | | | 42 | 2 | 16 8 | Iron. | 150, Paddle. | Glasgow (R. Napier). | 28th Oct. 1844. | | 355½ | 0-173° | 1-539 | +51 0 | | | | 42 | 2 | 16 8 | Iron. | 150, Paddle. | Glasgow (R. Napier). | 28th Oct. 1844. | * In these examples the compass was placed on the bridge before the funnel. † Above the level of iron bulwarks. ‡ Distance from iron bulwarks. | Date | Place of observation | Ship's name and Tonnage | Permanent coefficients | Coefficient | Ship's force to Head, Earth's horizontal force =1000 | Coefficient | Ship's force to Sternward, Earth's horizontal force =1000 | |------------|----------------------|-------------------------|------------------------|-------------|-------------------------------------------------|-------------|-------------------------------------------------| | | | | A. | D. | E. | B. | C. | | Jan. 26, 1849 | Portsmouth | JACKAL, 340 | -0° 13 | +4° 2 | +0° 22 | +12° 15 | 0° 2122 | -1° 39 | -0° 0288 | | Aug. 5, 1854 | Greenhithe | | +0° 18 | +2° 58 | +0° 38 | +14° 49 | 0° 2557 | -4° 12 | -0° 0732 | | May 10, 1859| Greenhithe | | +0° 10 | +3° 8 | -0° 35 | +15° 38 | 0° 2695 | -9° 31 | -0° 1653 | | Jan. 30, 1846| Greenhithe | HARRY, 343 | -0° 15 | +2° 54 | +0° 48 | +7° 3 | 0° 1227 | +2° 19 | 0° 0404 | | May 1, 1854 | Falmouth | | -1° 2 | +2° 41 | -0° 30 | +8° 43 | 0° 1515 | +0° 49 | 0° 0143 | | Dec. 23, 1857| Malta | | -0° 15 | +2° 50 | -0° 18 | +6° 14 | 0° 1036 | -0° 53 | -0° 0154 | | Mar. 6, 1860 | Greenhithe | | +0° 48 | +2° 32 | -0° 4 | +11° 12 | 0° 1942 | -1° 25 | -0° 0247 | | April 7, 1853| Sheerness | LIZARD, 340 | -0° 3 | +3° 49 | +0° 19 | +13° 31 | 0° 2337 | -2° 3 | -0° 0358 | | Feb. 8, 1858 | Sheerness | | +0° 34 | +2° 59 | +0° 53 | +10° 49 | 0° 1877 | +0° 36 | 0° 0105 | | Aug. 24, 1847| Portsmouth | FIREQUEEN, 313 | -0° 5 | +3° 27 | -0° 21 | +9° 14 | 0° 1605 | -7° 47 | -0° 1354 | | Nov. 8, 1852 | Portsmouth | | -0° 3 | +2° 53 | -0° 37 | +9° 48 | 0° 1702 | -5° 47 | -0° 1008 | | June 5, 1858 | Portsmouth | | +0° 17 | +2° 14 | +0° 8 | +4° 49 | 0° 0840 | +0° 51 | 0° 0148 | | July 8, 1845 | Greenhithe | FAIRY (Yaché), 312 | +0° 3 | +1° 58 | -0° 17 | +3° 55 | 0° 0683 | +1° 3 | 0° 0183 | | Mar. 22, 1849| Portsmouth | | +0° 35 | +2° 8 | +0° 22 | -7° 46 | 0° 1351 | -0° 32 | -0° 0093 | | Feb. 19, 1850| Portsmouth | | +0° 5 | +1° 50 | +0° 30 | -4° 20 | 0° 0756 | -1° 16 | -0° 0221 | | June 19, 1852| Portsmouth | | +0° 35 | +3° 33 | +0° 31 | +13° 25 | 0° 2320 | -1° 15 | -0° 0218 | | Jan. 23, 1858| Portsmouth | | -0° 33 | +3° 23 | +0° 6 | +11° 39 | 0° 2019 | -0° 33 | -0° 0096 | | June 5, 1854 | Greenhithe | MINX, 303 | +0° 15 | +3° 7 | -0° 6 | -1° 54 | 0° 0331 | -2° 20 | -0° 0407 | | Oct. 14, 1859| Greenhithe | | +1° 37 | +4° 29 | +0° 15 | -4° 48 | 0° 0837 | -4° 11 | -0° 0729 | | 1846 | Greenhithe | ONYX, 297 | -0° 18 | +3° 42 | -0° 24 | -7° 54 | 0° 1374 | -4° 16 | -0° 0744 | | 1848 | Greenhithe | | +0° 25 | +3° 36 | +0° 25 | -5° 30 | 0° 0958 | -3° 53 | -0° 0677 | | 1850 | Greenhithe | | +0° 39 | +3° 26 | +0° 27 | +2° 19 | 0° 0404 | -8° 23 | -0° 1458 | | Dec. 20, 1844| Greenhithe | PRINCESS ALICE, 270 | +0° 21 | +3° 1 | +0° 10 | +14° 54 | 0° 2571 | +0° 24 | 0° 0070 | | Dec. 26, 1850| Greenhithe | | -0° 7 | +2° 55 | 0° 0 | +12° 59 | 0° 2247 | -0° 19 | -0° 0055 | | April 15, 1855| Sheerness | | +2° 3 | +3° 36 | -0° 13 | +12° 1 | 0° 2082 | -2° 35 | -0° 0451 | | July 26, 1856| Greenhithe | | -0° 12 | +2° 32 | +0° 16 | +10° 5 | 0° 1751 | -1° 47 | -0° 0311 | | May 18, 1859 | Greenhithe | BANN, 267 | -2° 15 | +4° 15 | -0° 39 | +15° 6 | 0° 2605 | +14° 46 | 0° 2549 | * Fitted with iron tanks nearly the entire length of the vessel, for the purpose of carrying water. † After a thorough repair, new boilers and funnel, and Standard compass placed 6 inches further forward. ### Table I.—Iron-built Ships, Her Majesty's Navy (continued). | Direction | Resultant of B and C, or ship's Total force. | Magnetic elements. | Position of standard compass. | Beams. | Horse-power and engines. | Where built. | Date of launching. | |-----------|---------------------------------------------|---------------------|-------------------------------|--------|--------------------------|--------------|-------------------| | | | Horizontal force. | Dip. and nat. tang. | From funnel. | From taffrail. | Height from deck. | | | | | | ft. in. | ft. in. | ft. in. | Iron. | 150, Paddle. | Glasgow (R. Napier). | 28th October, 1844. | | 352° | 0·214 | 1·217 | +63° 0' 1·96 | 42 2 | 16 8 | 7 0 | | | | 344 | 0·266 | 1·000 | +68° 40' 2·56 | 42 2 | 16 8 | 7 0 | | | | 328½ | 0·316 | 1·000 | +68° 25' 2·53 | 41 0 | 15 0 | 5 5 | | | | 339 | 0·263 | 1·000 | +68° 25' 2·53 | 41 0 | 15 0 | 5 5 | | | | 18 | 0·129 | 1·000 | +68° 25' 2·53 | 43 0 | 14 0 | 5 3 | Wood, on quarter-deck. | 200, Paddle. | Blackwall (Ditchburn and Mare). | March, 1845. | | 6 | 0·152 | 1·000 | +68° 25' 2·53 | 43 0 | 14 0 | 4 10 | | | | 352° | 0·110 | 1·510 | +52° 0' 1·28 | 43 0 | 14 0 | 4 10 | | | | 353 | 0·166 | 1·000 | +68° 25' 2·53 | 43 0 | 14 0 | 4 10 | | | | 351 | 0·236 | 1·000 | +68° 40' 2·56 | 41 9 | 15 1 | 5 0 | Iron. | 150, Paddle. | Glasgow (R. Napier). | 28th November, 1844. | | 3 | 0·188 | 1·000 | +68° 40' 2·56 | 41 9 | 15 1 | 5 0 | | | | 5 | 0·172 | 1·000 | +68° 40' 2·56 | 41 9 | 15 1 | 5 0 | | | | 320 | 0·210 | 1·000 | +68° 30' 2·54 | 55 0 | 31 9 | | 120, Paddle. | Purchased July 1847. | | 329½ | 0·197 | 1·000 | +68° 30' 2·54 | 55 0 | 31 9 | | | | | 10 | 0·085 | 1·000 | +68° 30' 2·54 | 62 9 | 25 0 | 3 7 | | | | 15 | 0·070 | 1·000 | +68° 30' 2·54 | unknown. | | | Wood. | 120, Screw. | Blackwall (Ditchburn and Mare). | March, 1845. | | 184 | 0·135 | 1·000 | +68° 30' 2·54 | 52 0 | 15 0 | 2 9½ | | | | 196 | 0·079 | 1·000 | +68° 30' 2·54 | 48 10 | 15 2 | 2 9 | | | | 355 | 0·233 | 1·000 | +68° 30' 2·54 | 26 0 | 39 0 | 2 8 | | | | 357 | 0·202 | 1·000 | +68° 30' 2·54 | 26 0 | 39 0 | 2 8 | | | | 10 | 0·201 | 1·000 | +68° 30' 2·54 | 26 0 | 39 0 | 2 8 | | | | 231 | 0·052 | 1·000 | +68° 30' 2·54 | 18 0 | 18 0 | 5 0 | 100, Screw. | Blackwall (Wigram). | 5th September, 1846. | | 221 | 0·111 | 1·000 | +68° 30' 2·54 | 36 0 | 9 6 | 3 6 | | | | 209 | 0·157 | 1·000 | +68° 30' 2·54 | 23 0 | | | 120, Paddle. | Blackwall (Ditchburn and Mare). | November, 1845. | | 215 | 0·117 | 1·000 | +68° 30' 2·54 | 23 0 | | | | | | 285 | 0·151 | 1·000 | +68° 30' 2·54 | 22 6 | | | | | | 2 | 0·257 | 1·000 | +68° 30' 2·54 | 22 0 | 35 6 | 5 10 | Wood. | 120, Paddle. | Blackwall. | 1843. | | 358 | 0·225 | 1·000 | +68° 30' 2·54 | 22 0 | 35 6 | 5 10 | | | | 348 | 0·213 | 1·000 | +68° 30' 2·54 | 22 0 | 35 6 | 5 10 | | | | 350 | 0·178 | 1·000 | +68° 30' 2·54 | 26 5 | 34 0 | 5 10 | | | | 44½ | 0·364 | 1·000 | +68° 30' 2·54 | 49 0 | 29 0 | 4 7 | Iron. | 80, Paddle. | Millwall (J. S. Russell). | 5th July, 1856. | MDCCCLX. ### Table I.—Iron-built Ships, Her Majesty's Navy (continued). | Date | Place of observation | Ship's name and Tonnage | Permanent coefficients | Coefficient | Ship's force to Horse- Earth's horizontal force =1000. | Coefficient | Ship's force to Starboard- Earth's horizontal force =1000. | |---------------|----------------------|-------------------------|------------------------|------------|-----------------------------------------------------|------------|----------------------------------------------------------| | May 25, 1857. | Sheerness | BRUNE, 267..............| -0 35 +6 22 +0 56 -9 15 | -0 1607 +3 28 | 0 0605 | | Aug. 7, 1849. | Penetanguishine, Lake Huron, Canada. | MOHAWK, 228.............| -1 28 +3 1 -1 47 +10 15 | 0 1779 -8 5 | -0 1406 | | 1846. | Greenhithe | TORCH, 343..............| -0 26 +2 56 +0 5 +11 8 | 0 1931 -4 3 | -0 0706 | | May 10, 1852. | Greenhithe | | -0 4 +2 43 +0 24 +10 41 | 0 1854 -0 46 | -0 0134 | | July 6, 1852. | Madeira | | +3 2 +2 52 -0 5 +6 25 | 0 1117 -1 20 | -0 0233 | | July 22, 1852.| St. Vincent, Cape de Verd Islands. | | +2 43 +2 10 -0 43 +6 52 | 0 1196 -0 57 | -0 0166 | | Sept. 29, 1852.| Rio de Janeiro | | -0 7 +2 29 +0 9 +7 17 | 0 1268 -1 6 | -0 0192 | | Nov. 16, 1852.| Tristan d'Aouinha | | +0 12 +2 23 -0 56 +7 42 | 0 1340 -3 13 | -0 0561 | | Dec. 10, 1852.| Cape of Good Hope | | -1 17 +1 57 +0 6 +9 18 | 0 1616 +0 30 | 0 0087 | | Jan. 26, 1853.| St. Paul's Island, Indian Ocean. | | +1 58 +1 39 +0 6 +10 17 | 0 1785 -0 28 | -0 0081 | | Feb. 18, 1853.| Swan River, Australia | | -1 5 +1 31 -0 15 +6 58 | 0 1213 -0 13 | -0 0038 | | Mar. 15, 1853.| King George's Sound | | -2 8 +2 44 +0 44 +8 41 | 0 1510 -1 13 | -0 0212 | | July 1856. | East Coast, Australia | | +0 25 +1 37 -0 11 +8 18 | 0 1443 +0 23 | 0 0067 | | May 11, 1844. | Woolwich | DOVER, 224..............| +1 14 +2 38 +0 8 -6 57 | -0 1210 -4 10 | -0 0727 | | Sept. 25, 1849.| Plymouth | | +0 2 +2 23 -0 18 -4 58 | -0 0866 +0 25 | 0 0073 | | June 23, 1843.| Greenhithe | WILBERFORCE, 457........| +0 33 +2 18 +0 15 -7 48 | -0 1357 -7 15 | -0 1262 | | July 5, 1843. | River Gambia | | 0 0 +2 6 +0 7 -4 39 | -0 0811 -4 12 | -0 0732 | | Jan. 13, 1844.| Greenhithe | DWARF, 164..............| -0 35 +2 2 +0 17 +13 5 | 0 2264 -3 8 | -0 0547 | ### Table II.—Floating Batteries*, Her Majesty's Navy. | Date | Place of observation | Ship's name and Tonnage | Permanent coefficients | Coefficient | Ship's force to Horse- Earth's horizontal force =1000. | Coefficient | Ship's force to Starboard- Earth's horizontal force =1000. | |---------------|----------------------|-------------------------|------------------------|------------|-----------------------------------------------------|------------|----------------------------------------------------------| | July 1857. | Sheerness | TERROR, 1971............| -1 45 +6 17 -0 44 +25 12 | 0 4258 +2 3 | 0 0358 | | July 5, 1855. | Greenhithe | METEOR..................| -1 19 +0 12 0 0 -1 19 | -0 0230 -3 31 | -0 0613 | | Mar. 31, 1856.| Sheerness | THUNDER, 1469...........| +0 34 -0 40 +0 9 -11 33 | -0 2002 -1 33 | -0 0270 | | Mar. 26, 1856.| Sheerness | TRUSTY, 1539............| +0 4 +1 37 -1 54 -16 55 | -0 2910 +3 52 | 0 0674 | *Of these, TERROR is the only Iron-built vessel; the others are Wood-built plated with iron. ### Table I.—Iron-built Ships, Her Majesty's Navy (continued). | Direction | Amount | Magnetic elements | Position of standard compass | Beams | Horse-power and engines | Where built | Date of launching | |-----------|--------|-------------------|------------------------------|-------|-------------------------|------------|------------------| | | | Horizontal force | Dip, and nat. tang. | ft. in. | ft. in. | ft. in. | Iron. | Millwall (J. S. Russell). | 30th August, 1856. | | 159½ | 0·171 | 1·000 | +68° 30' 2°54' | 45 | 3 | 28 | 8 | 4 | 4 | Iron. | 80, Paddle. | Limehouse (Fairburn and Co.). | Kingston, Upper Canada. | 21st Feb. 1843†. | | 321 | 0·227 | 0·876 | +76° 0' 4°01' | 10 | 0 | 10 | 0 | 10 | 0 | Iron. | 60, Paddle. | Blackwall (Ditchburn and Mare). | February, 1845. | ### Table II.—Floating Batteries, Her Majesty's Navy (continued). | 5 | 0·426 | 1·000 | +68° 25' 2°53' | 70 | 0 | 37 | 0 | 5 | 5 | Iron. | Screw. | Newcastle-on-Tyne (Palmer). | 26th April, 1856. | |-----------|--------|-------------------|------------------------------|--------|--------|--------|--------|--------|--------|-------|--------|---------------------------------|------------------| | 249 | 0·065 | 1·000 | +68° 25' 2°53' | 79 | 0 | 16 | 6 | 4 | 8 | Wood. | Screw. | | | | 188 | 0·202 | 1·000 | +68° 25' 2°53' | 83 | 0 | 10 | 10 | 4 | 7 | Wood. | Screw. | | | | 167 | 0·299 | 1·000 | +68° 25' 2°53' | 84 | 0 | 9 | 10 | 4 | 6 | Wood. | Screw. | | | † Delivered in parts at Woolwich, November 1841. ### Table III.—Screw Steam-vessels, Her Majesty's Navy (Wood-built). | Date | Place of observation | Ship's name and Tonnage | Permanent coefficients | Coefficient | Ship's force to 1/10th Earth's horizontal force =1000 | |------------|----------------------|--------------------------|------------------------|-------------|---------------------------------------------------| | April 29, 1859 | Portsmouth | Mersey, 3739 | +0 52 | -0 15 | -0 5 | + 7 44 | 0-1346 | | Jan. 5, 1860 | Sheerness | Ariadne, 3202 | +0 8 | +0 31 | -0 12 | + 8 37 | 0-1498 | | Mar. 29, 1859 | Plymouth | Doris, 2479 | +1 11 | -0 30 | +0 43 | + 7 11 | 0-1250 | | Jan. 7, 1856 | Plymouth | Sanspareil, 2334 | +0 4 | +0 58 | -0 13 | +23 43 | 0-4022 | | May 22, 1857 | Cape of Good Hope | | -0 37 | +1 16 | +0 36 | + 3 41 | 0-0642 | | | Canton | | +0 8 | +0 53 | -0 7 | + 7 41 | 0-1337 | | Oct. 20, 1859 | Portsmouth | Arrogant, 1872 | -0 32 | +0 20 | +0 10 | + 6 21 | 0-1106 | | Sept. 5, 1859 | Sheerness | Clio, 1470 | -0 43 | +0 56 | +0 4 | + 9 39 | 0-1676 | | June 1, 1859 | Sheerness | Cadmus, 1462 | -0 23 | -0 20 | -0 4 | +11 1 | 0-1911 | | June 7, 1856 | Portsmouth | Pylares, 1278 | +1 22 | +0 27 | -1 6 | +12 48 | 0-2215 | | Sept. 9, 1856 | Sydney, C. Breton Island | | -0 6 | 0 0 | -0 12 | +17 47 | 0-3054 | | Sept. 26, 1856 | Portsmouth | Highflyer, 1161 | +0 52 | +0 36 | +0 13 | +11 42 | 0-2028 | | Dec. 12, 1856 | Rio de Janeiro | | +1 4 | -0 42 | +0 7 | + 4 49 | 0-0840 | | Feb. 1857 | Cape of Good Hope | | -0 50 | -0 23 | -0 8 | + 4 20 | 0-0755 | | May 26, 1857 | Hong Kong | | +0 7 | -0 32 | +0 10 | + 3 21 | 0-0584 | | Dec. 2, 1857 | Canton River | | +0 15 | +0 6 | +0 10 | + 3 45 | 0-0654 | | May 17, 1858 | Shanghai | | -0 3 | -0 5 | +0 39 | + 6 25 | 0-1118 | | May 23, 1859 | Portsmouth | Falcon, 992 | +0 15 | +0 10 | -0 25 | + 6 37 | 0-1152 | | | Plymouth | Encounter, 953 | +0 29 | +0 27 | -0 3 | + 7 1 | 0-1222 | | Nov. 28, 1859 | Greenhithe | Mutine, 875 | +0 12 | -0 19 | -0 10 | + 8 35 | 0-1492 | | Nov. 19, 1859 | Sheerness | Fawn, 748 | +0 16 | +0 42 | -0 40 | + 7 21 | 0-1279 | | May 21, 1857 | Plymouth | Cordelia, 579 | +0 19 | -0 40 | -0 5 | + 7 57 | 0-1383 | | Aug. 3, 1857 | Cape of Good Hope | | +1 5 | +0 20 | -0 22 | - 1 12 | 0-0209 | | Sept. 20, 1858 | Apia, Upolu, Pacific Ocean | | -0 27 | +0 40 | +1 1c | + 1 24 | 0-0244 | | Mar. 7, 1857 | Portsmouth | Plumper, 490 | +0 14 | +0 52 | +0 5 | + 6 1 | 0-1048 | | April 1857 | Lisbon | | +0 4 | -0 10 | -0 18 | +4 39 | 0-0811 | | May 1857 | Rio de Janeiro | | -0 49 | +0 47 | +0 14 | + 2 8 | 0-0372 | | Sept. 1, 1857 | Valparaiso | | +0 6 | +0 37 | +0 37 | + 1 6 | 0-0192 | | Oct. 1857 | Sandwich Islands | | -0 49 | +0 26 | +0 5 | + 2 17 | 0-0398 | | Jan. 30, 1858 | Vancouver I., Esquimalt | | -0 13 | +0 23 | -0 3 | + 5 45 | 0-1002 | | June 17, 1859 | Vancouver I., Nanaimo | | +0 52 | +0 5 | +0 5 | + 6 26 | 0-1120 | | Jan. 1, 1856 | Greenhithe | Tickler (Gun-boat), 232 | -1 37 | +1 26 | -0 13 | + 0 15 | 0-0043 | ### Table III.—Screw Steam-vessels, Her Majesty's Navy (Wood-built) (continued). | Coefficient | Ship's force to starboard. Earth's horizontal force =1'000. | Resultant of B and C, or ship's Total force. | Magnetic elements. | Position of standard compass. | Horse-power of engines. | |-------------|-------------------------------------------------|-----------------------------------------------|-------------------|-------------------------------|------------------------| | | Direction. Amount. | Horizontal force. | Dip, and nat. tang. | From funnel. | Height from deck. | | +1 23 | 0·0241 10° 0·137 1·000 | +68 15 | ft. in. | ft. in. | 1000 | | -2 26 | -0·0424 344° 0·156 1·000 | +68 15 | 119 0 | 6 3 | 800 | | -1 15 | -0·0218 350° 0·127 1·000 | +68 15 | 110 0 | 6 11 | 800 | | +1 45 | 0·0305 4½° 0·404 1·000 | +68 15 | 19 4 | On poop. | 400 | | +2 8 | 0·0372 30° 0·074 1·174 | -54 42 | 19 4 | 400 | | +0 57 | 0·0166 7° 0·135 2·049 | +31 30 | 19 4 | 400 | | -0 28 | -0·0081 356° 0·111 1·000 | +68 15 | 68 0 | 6 7 | 360 | | +4 46 | 0·0831 26½° 0·187 1·000 | +68 15 | 80 0 | 7 6 | 400 | | +2 35 | 0·0451 13° 0·196 1·000 | +68 15 | 87 0 | 6 6 | 400 | | +4 23 | 0·0764 19° 0·234 1·000 | +68 15 | 350 | | +5 22 | 0·0935 17° 0·320 0·772 | +76 30 | 417 | | +0 48 | 0·0140 4° 0·203 1·000 | +68 15 | 70 0 | 6 0 | 250 | | +0 8 | 0·0023 2° 0·084 1·708 | -11 21 | 70 0 | 6 0 | 360 | | -1 18 | -0·0227 343° 0·079 1·174 | -54 42 | 70 0 | 6 0 | 200 | | +0 29 | 0·0084 8° 0·059 2·049 | +31 26 | 70 0 | 6 0 | 200 | | +0 9 | 0·0026 2° 0·065 2·049 | +32 35 | 70 0 | 6 0 | 200 | | +0 20 | 0·0058 3° 0·112 1·813 | +45 18 | 70 0 | 6 0 | 200 | | -2 39 | -0·0462 338° 0·124 1·000 | +68 15 | 71 0 | 7 0 | 100 | | +0 10 | 0·0029 1° 0·122 1·000 | +68 15 | 73 0 | 5 5 | 360 | | -2 50 | -0·0494 342° 0·157 1·000 | -68 15 | 70 0 | 6 6 | 200 | | -1 55 | -0·0334 345½° 0·132 1·000 | +68 15 | 71 0 | 6 7 | 100 | | -0 27 | -0·0078 357° 0·139 1·000 | +68 15 | 64 0 | 6 5 | 150 | | +1 40 | 0·0291 126° 0·036 1·174 | -54 42 | 64 0 | 6 5 | 150 | | -0 26 | -0·0076 343° 0·025 2·083 | -35 30 | 64 0 | 6 5 | 150 | | +1 13 | 0·0212 11° 0·107 1·000 | +68 15 | 38 7 | 5 6 | 60 | | +1 8 | 0·0198 13° 0·083 1·216 | +61 5 | 38 7 | 5 6 | 60 | | +0 32 | 0·0093 14° 0·038 1·709 | -11 21 | 38 7 | 5 6 | 60 | | +0 3 | 0·0008 2° 0·019 1·887 | -0 20 | 38 7 | 5 6 | 60 | | +0 20 | 0·0058 8° 0·040 1·028 | -35 37 | 38 7 | 5 6 | 60 | | +0 55 | 0·0160 9° 0·102 1·040 | -42 00 | 38 7 | 5 6 | 60 | | +0 29 | 0·0084 5° 0·112 1·016 | +72 25 | 38 7 | 5 6 | 60 | | -0 57 | -0·0166 285° 0·017 1·000 | +68 15 | 35 0 | 3 7 | 60 high pressure | | Date | Place of observation | Ship's name and Tonnage | Permanent coefficients | Coefficient | Ship's force to Head, English horizontal force =1'000. | Coefficient | Ship's force to Starboard, English horizontal force =1'000. | Resultant of B and C, or ship's Total force. | Magnetic elements | Position of standard compass | Horsepower of engines | |------------|---------------------|-------------------------|------------------------|-------------|-------------------------------------------------|-------------|-------------------------------------------------|----------------------------------|----------------------|--------------------------|-----------------------| | May 27, 1846 | Greenhithe | Terrible, 1847. | -0 12 | +0 55 | +0 8 | +3 05 | 0-0886 | +0 10 | 0-0029 | 2 0-089 | 1-000 | 69 0 ft. in. | 33 9 ft. in. | 800 | | Dec. 26, 1845 | Sheerness | Retribution, 1641. | -0 48 | +1 22 | +0 7 | +10 21 | 0-1797 | +4 20 | 0-0755 | 23 0-195 | 1-000 | +69 0 ft. in. | 57 6 ft. in. | 79 | | Oct. 8, 1856 | Sheerness | Callao | -1 7 | +0 30 | +0 20 | +9 33 | 0-1659 | +4 27 | 0-0776 | 25 0-183 | 1-000 | +69 0 ft. in. | 57 6 ft. in. | 79 | | Aug. 17, 1857 | Callao | Hong Kong | +0 18 | +0 12 | -0 1 | +4 29 | 0-0782 | +1 16 | 0-0221 | 16 0-054 | 1-963 | -7 0 ft. in. | 31 26 ft. in. | 61 | | Mar. 1859 | | Penelope, 1616. | +0 17 | +1 25 | +0 21 | +7 24 | 0-1288 | +0 18 | 0-0052 | 2 0-129 | 1-000 | 69 0 ft. in. | 35 0 ft. in. | | | Sept. 1843 | | Cyclops, 1106. | -0 15 | +2 10 | -0 1 | +6 51 | 0-1193 | -1 9 | -0-0201 | 350 0-121 | 1-000 | +68 30 ft. in. | 38 6 ft. in. | 43 | | May 29, 1857 | Sheerness | St. John's, Newfoundland | +0 28 | +1 34 | +0 36 | +9 31 | 0-1653 | -1 1 | -0-0177 | 354 0-166 | 0-776 | +76 0 ft. in. | 38 6 ft. in. | 43 | | Aug. 17, 1857 | Kurrachee | Portsmouth | +0 16 | +1 17 | +0 24 | +2 26 | 0-0424 | -0 10 | -0-0029 | 356 0-042 | 2-012 | +28 15 ft. in. | 38 6 ft. in. | 43 | | Dec. 1859 | | Sphynx, 1056. | +0 15 | +1 50 | -0 18 | +8 58 | 0-1558 | +0 23 | 0-0067 | 2 0-156 | 1-000 | 69 0 ft. in. | 32 3 ft. in. | | | Sept. 5, 1848 | Hong Kong | Geyser, 1054. | +0 2 | +1 14 | -0 4 | +9 12 | 0-1599 | -2 3 | -0-0358 | 347 0-164 | 1-000 | 69 0 ft. in. | 33 0 ft. in. | | | 1847 | | C.of Good Hope | -0 46 | +0 59 | +0 11 | -2 12 | 0-0384 | -0 56 | -0-0163 | 203 0-042 | 1-174 | -54 42 ft. in. | 141 ft. in. | | | Oct. 17, 1857 | Plymouth | Styx, 1057 | +1 30 | +1 37 | +0 3 | +5 33 | 0-0967 | 0 0 | 0-0000 | 360 0-097 | 1-000 | +68 30 ft. in. | 36 10 ft. in. | 57 | | July 1859 | Halifax, N.S. | Port Nicholson, New Zealand | +0 54 | -0 33 | -0 16 | +1 26 | 0-0250 | -1 47 | -0-0311 | 309 0-040 | 1-382 | -65 0 ft. in. | 214 ft. in. | | | 1847 | | Acheron, 720. | +0 23 | +0 58 | +0 3 | +7 43 | 0-1343 | +2 23 | 0-0416 | 17 0-141 | 1-000 | 68 40 ft. in. | 30 0 ft. in. | 50 | | 1850 | | Port Nicholson, New Zealand | +0 54 | -0 33 | -0 16 | +1 26 | 0-0250 | -1 47 | -0-0311 | 309 0-040 | 1-382 | -65 0 ft. in. | 214 ft. in. | | ### Table V.—Steam-Ship Great Eastern (Iron-built). | Date | Place of observation | Vessel's name and Tonnage | Permanent coefficients | Ship's force to Head. Earth's horizontal force = 1'000. | Resultant of B and C, or ship's Total force | Position of compass | |--------------|----------------------|----------------------------|------------------------|-----------------------------------------------------|---------------------------------------------|---------------------| | | | | A. D. E. B. | Coefficient | Direction. Amount. | | | | | | | | | | **By Admiralty Standard Compass.** | Sept. 7, 1859 | River Thames... | GREAT EASTERN, 22,000 | -6 10 +4 21 -6 37 +23 13 | 0·3942 +25 38 0·4326 47° 0·585 ft. in. | |--------------|----------------------|----------------------------|--------------------------|----------------------------------------------------|---------------------------------------------|---------------------| | Sept. 10, 12, 1859 | Portland | | -1 3 +4 44 -0 45 +22 42 | 0·3859 +16 43 0·2876 37° 0·480 Height from deck... 4 ft. 11 in. | | Oct. 22, 24, 1859 | Holyhead | | -0 24 +4 8 -0 17 +19 18 | 0·3305 +12 3 0·2088 32° 0·390 From rudder head... 41 ft. 0 in. | | | | | | | | | **Mast Compass, 45 feet from deck.** | Sept. 7, 1859 | River Thames... | | +0 4 +1 32 +0 4 +12 43 | 0·2201 +11 12 0·1942 41° 0·295 Mast Compass... 41 ft. 0 in. | |--------------|----------------------|----------------------------|------------------------|----------------------------------------------------|---------------------------------------------|---------------------| | Sept. 10, 12, 1859 | Portland | | +1 21 +1 30 -0 10 +16 12 | 0·2790 +4 20 0·0756 15° 0·290 " spindle of capstan... 17 ft. 6 in. | | Oct. 22, 24, 1859 | Holyhead | | +2 20 +1 0 +0 7 +17 2 | 0·2929 +7 30 0·1305 24° 0·320 " nearest funnel... 165 ft. 0 in. | | | | | | | | | **Platform Compass.** | Sept. 7, 1859 | River Thames... | | -1 40 +7 55 -0 12 +13 34 | 0·2346 +22 41 0·3856 59° 0·455 Platform Compass... see Plate XV. | |--------------|----------------------|----------------------------|------------------------|----------------------------------------------------|---------------------------------------------|---------------------| | Sept. 10, 12, 1859 | Portland | | +0 43 +5 19 +0 40 +10 17 | 0·1785 +21 5 0·3597 64° 0·405 " | | | | | | | | | **Foremost Bridge Compass.** | Sept. 7, 1859 | River Thames... | | +0 3 +4 31 -0 9 +31 55 | 0·5287 +17 47 0·3054 30° 0·610 Foremost Bridge Compass... | |--------------|----------------------|----------------------------|------------------------|----------------------------------------------------|---------------------------------------------|---------------------| | | | | | | | | SUPPLEMENT. [Added during the printing of the paper.] In June 1860, prior to the departure of the steam-ship Great Eastern on her first Atlantic voyage, I was enabled, through the attention and cooperation of the captain, John V. Hall, and managing director, T. Bold, Esq., to institute further experiments on the changes of the ship’s magnetism, under the same conditions as those already recorded as having been made in the River Thames, at Portland, and at Holyhead, in September and October 1859. Subsequent to the observations made at Holyhead, the Great Eastern rode out a violent gale in that harbour,—remarkable as causing the total wreck of the ship Royal Charter in the immediate neighbourhood,—which necessarily subjected many parts of the hull to severe concussion from the strain on the cables: the ship’s services were then confined to the passage to Southampton; and during the sojourn at that port for the following seven months, she quietly swung round the moorings to the tides and variable winds. Extensive artificers’ works were latterly performed in the internal equipments. These details are worthy of notice, from the striking progressive diminution of the ship’s magnetic force, and further tendency to the fore-and-aft direction of the neutral points of disturbance which the Southampton observations developed. The same Admiralty standard compass having been placed in the exact position of former experiments, the correct magnetic bearing of the extreme point of the Isle of Wight, visible from the anchorage (distant 12 miles), was determined from a series of astronomical bearings and the known magnetic variation of the place, the necessary correction for parallax due to the length of the ship being allowed for the successive points of the compass as the ship swung round. From the wind prevailing in one direction for several days prior to the departure of the Great Eastern, I was only able, although engaged on the 13th, 14th, and 15th of June, to obtain the deviations on sixteen and a half consecutive points; namely, from S.S.E., by the South, to N.N.W. $\frac{1}{2}$ W.: these deviations, resulting from a curve drawn through fifty-one separate determinations, made under highly favourable circumstances, were as follows:— | Ship's head by Stand: comp: | Deviation. | Head by Stand: comp: | Deviation: | Head by Stand: comp: | Deviation. | |---------------------------|------------|---------------------|-----------|---------------------|-----------| | S.S.E. | 2° 0 E. | S.W. | 6° 30 W. | W.N.W. | 14° 50 W. | | S. by E. | 0° 20 E. | S.W. by W. | 8° 25 W. | N.W. by W. | 14° 15 W. | | South | 1° 40 W. | W.S.W. | 10° 15 W. | N.W. | 12° 50 W. | | S. by W. | 3° 40 W. | W. by S. | 12° 0 W. | N.W. by N. | 10° 10 W. | | S.S.W. | 4° 45 W. | West | 13° 0 W. | N.N.W. ½ W. | 8° 0 W. | | S.W. by S. | 5° 30 W. | W. by N. | 14° 20 W. | | | It was necessary to deduce from these results the probable values for the remaining points of the compass; this appeared to be obtained with sufficient accuracy by trials of the coefficients B, C, D, with various assumed values, adopting those, the deviations resulting from which should approximate most closely to the actual observed deviations on the sixteen and a half determined points. The coefficients A and E were, under the circumstances, assumed as 0° 0'. The resulting values for B of +13° 30', C+1° 40', D+4° 20', afforded a satisfactory approximation; from whence the ship's force in direction and amount are respectively 7° and 0·235, the earth's horizontal magnetic force being considered, as at the other ports, 1·000. A recapitulation of the Great Eastern's total magnetic force at each place of observation is herewith appended, as also a Table of deviations, which brings practically to view the change in the deviation of the mariners compass in a newly launched iron vessel, amounting in this special case to a decrease of 12° on some points of the compass in the first five days, 19° in seven weeks, and nearly three points, or 32° 10' in the first nine months of service afloat. | Date | Angle of force from ship's head | Total force | Earth's horizontal force | |-----------------------|---------------------------------|-------------|--------------------------| | 1859. September 7, River Thames | 47° | 0·585 | 1·000 | | " 10—12, Portland | 37° | 0·480 | " | | " Oct. 22—24, Holyhead | 32° | 0·390 | " | | 1860. June 13—15, Southampton | 7° | 0·235 | " | Deviations of the Compass observed on board the steam-ship *Great Eastern*, 1859–60; in a position on the upper deck, in the middle line of the ship; distant 46 feet 4 inches from the after or jigger mast; 17 feet 6 inches before the spindle of the after capstan, and 41 feet 0 inches before the rudder head; the needle elevated 4 feet 11 inches from the deck. | Ship's head, correct magnetic. | River Thames, 7th September, 1859. | Portland, 10th to 12th Sept. 1859. | Holyhead, 22 to 24th October, 1859. | Southampton, 13th, 14th, 15th June, 1860. | |-------------------------------|----------------------------------|----------------------------------|----------------------------------|----------------------------------| | North. | 15° 50' E. | 9° 20' E. | 7° 0' E. | 1° 15' E. | | N. by E. | 21° 0" | 14° 40" | 10° 50" | 4° 30" | | N.N.E. | 25° 0" | 19° 25" | 14° 50" | 7° 25" | | N.E. by N. | 29° 0" | 23° 0" | 18° 10" | 10° 0" | | N.E. | 32° 0" | 26° 30" | 21° 20" | 12° 40" | | N.E. by E. | 36° 0" | 29° 20" | 24° 0" | 14° 50" | | E.N.E. | 38° 10" | 31° 0" | 25° 30" | 16° 10" | | E. by N. | 39° 0" | 31° 15" | 26° 0" | 16° 50" | | East. | 38° 0" | 30° 10" | 25° 0" | 16° 0" | | E. by S. | 32° 30" | 26° 0" | 22° 0" | 14° 0" | | E.S.E. | 22° 0" | 20° 20" | 17° 0" | 11° 30" | | S.E. by E. | 6° 0" | 12° 0" | 9° 20" | 8° 30" | | S.E. | 10° 30 W. | 0° 0" | 1° 15" | 5° 30" | | S.E. by S. | 23° 40" | 11° 00 W. | 5° 40 W. | 3° 0" | | S.S.E. | 29° 30" | 17° 40" | 10° 50" | 2° 40" | | S. by E. | 31° 20" | 21° 30" | 14° 20" | 0° 20" | | South. | 31° 30" | 23° 0" | 16° 30" | 2° 0 W. | | S. by W. | 30° 50" | 23° 45" | 17° 40" | 4° 0" | | S.S.W. | 29° 30" | 23° 50" | 18° 15" | 5° 10" | | S.W. by S. | 27° 30" | 23° 50" | 18° 40" | 6° 0" | | S.W. | 25° 30" | 23° 10" | 18° 50" | 8° 0" | | S.W. by W. | 23° 40" | 22° 40" | 19° 0" | 10° 0" | | W.S.W. | 21° 30" | 21° 45" | 18° 40" | 11° 50" | | W. by S. | 19° 0" | 20° 30" | 18° 0" | 13° 30" | | West. | 16° 0" | 18° 45" | 17° 0" | 14° 30" | | W. by N. | 13° 20" | 16° 30" | 15° 30" | 14° 40" | | W.N.W. | 10° 0" | 13° 40" | 13° 10" | 14° 0" | | N.W. by W. | 6° 40" | 10° 50" | 10° 20" | 12° 30" | | N.W. | 3° 0" | 8° 0" | 7° 0" | 10° 30" | | N.W. by N. | 1° 10 E. | 4° 35" | 3° 40" | 7° 45" | | N.N.W. | 5° 40" | 0° 20" | 0° 0" | 5° 0" | | N. by W. | 10° 30" | 4° 10 E. | 3° 30 E. | 2° 0" | Sketch shewing the Magnetic character of the topsides, the positions of the several Com Sketch of the S.S. Great Eastern, shewing the external ne Note. The broad continuous, and non-continuous lines, September 1857. The small dotted lines, are approximately in November 1857. {Dark lines and figures; Port side of the Ship. {Light ditto Starboard Deviation of the Compass (in degrees) {The observations with a dot, which denotes the position.) encircled Sketch of the S.S. Great Eastern, shewing the external neutral Magnetic Lines, or, the separation between the North & South polarities. Note. The broad continuous and non-continuous lines, September 15, 1859, at Deptford. The small dotted lines, are approximately in November 1857, prior to launching. (Dark lines and figures; Port side of the Ship. (Light ditto Starboard. (The observations with a dot, which denotes the position, are those made in 1859.) + East Deviation. - West Deviation Direction (in degrees) TEAM SHIP EASTERN. Phil Trans MDCCCLX Plate XV. Masts of Machinery within these dotted lines. Platform Compass Admiralty Standard Compass (compensated) (temporarily placed for experiments) Mast Compass (temporarily removed from deck) Platform Compass (Compensated) (temporarily removed from deck) North Polarity South Polarity Direction of Keel and Head while building S.29°50'E Mag't at Deptford S.46°0'E. Scale of feet Direction of Magnetic Lines, or, the separation between the North & South polarity of the Hull. 1859, at Deptford. Prior to launching. Direction made in 1859 East Deviation, -West Deviation 1857 Diagrams shewing Polarity of the topsides of an Iron vessel according to the direction in which her Head may be built with reference to the Magnetic meridian. Head built. | North | B | C | |-------|---|---| | N.E. | B | C | | East | B | C | | S.E. | B | C | | South | B | C | | S.W. | B | C | | West | B | C | | N.W. | B | C | Note: - Indicates South polarity (repelling north end of needle). - The intensity of the shading a corresponding intensity of Magnesia. - A, is the general position of the Standard Compass in Ships. - The arrow indicates the direction of the Ship's force. J. Batire Sc.