Account of Magnetic Observations Made in the Years 1858-61 Inclusive, in British Columbia, Washington Territory, and Vancouver Island

III. Account of Magnetic Observations made in the years 1858–61 inclusive, in British Columbia, Washington Territory, and Vancouver Island. By Captain R. W. Haig, R.A. Communicated by General Sabine, P.R.S. Received November 4,—Read November 26, 1863. In 1858 a Commission was appointed for the purpose of determining and marking the forty-ninth parallel of north latitude from the Pacific to the Rocky Mountains. At the suggestion of General Sabine, this Commission was provided with a set of portable magnetic instruments adapted for the determination of the three magnetic elements, Dip, Declination, and Total Force. These instruments were similar in kind to those which had been used on the Magnetic Survey of the United Kingdom. Before delivery to the Boundary Commission they were examined at the Kew Observatory, and several constants and tables for facilitating the computations were determined and prepared there. The method of transporting the instruments from place to place, and indeed everything appertaining to the Boundary Commission, was by means of packet mules. Two boxes (a very light load for one mule) contained all the magnetic instruments, which throughout four years of such rough usage retained their original efficiency. Some of the needles became somewhat rusted; but I can suggest no alteration in the construction of such instruments, such as would increase their portability. The declinometer was, I think, unsatisfactory as regarded its capability of determining azimuths of the sun: when at an astronomical station, I necessarily had a meridian mark for the transit instrument, and I referred the direction of the magnet to such meridian. In assembling the results and deducing from them the directions and positions of the lines of equal dip, force, and declination, no notice has been taken of secular change. The only station at which we have data for judging of the extent of secular change is Fort Vancouver on the Columbia River. As regards dip, we find there | Year | Dip | Observer | |------|-------|----------------| | 1830 | 69° 39'7" | Douglas | | 1839 | 69° 22'2" | Sir E. Belcher | | 1860 | 69° 17'4" | Present observations | These figures show an annual diminution of dip of less than 1' per annum. The mean results of the present observations may be assumed to belong to the year 1860. The method of assembling the results and determining from them the position and direction of the lines of equal dip, force, and declination, is the same as that adopted in the Survey of the United Kingdom. It consists in referring all the results to the point of mean longitude and latitude among all the stations, and assuming the differences of longitude and latitude expressed in geographical miles to be plane rectangular coordinates of distance from the origin. It is also assumed that the three magnetic elements vary uniformly over the whole district surveyed. **Dip.** Table I. gives the individual results at each station, as well as the partial results from the needle when magnetized in opposite directions. Table II. shows the mean results, along with the most probable dip at each station computed by the method of minimum squares. By the method of minimum squares the variation of dip for one mile of longitude $x = +0^\circ 272$, and the variation for one mile of latitude $y = +0^\circ 776$; from these values we get $\theta = 70^\circ 42'$ for the angle which an isoclinal line makes with the meridian measured from the north round by west, and $\frac{1}{r}$ or $\frac{1}{\sqrt{x^2+y^2}} = 1.216$ mile for the distance between isoclinals whose difference of dip is $1'$. Column 5 contains the most probable dip at each station ($\theta'$), obtained from equations $\theta' = \theta_1 + ax + by$. The probable error of the computed dip at each station is nearly equal to $\pm 5'$. **Intensity of the Magnetic Force.** The stations where these observations were made are the same as the dip stations. At ten of them observations of deflection and vibration for the horizontal component were made with the unifilar, and observations by Lloyd's statical method for variation of the total force; at the remaining eleven stations the statical method only was employed. Observations at the first ten stations furnish values of the constant log $A$, of which a mean value might be adopted for use at the other eleven; but from an examination of these values of log $A$, it appears that those belonging to 1861 are generally larger than preceding values, owing, I believe, to the weighted needle having become rusted. I have therefore adopted the mean of all values of log $A$ previous to 1861 for statical observations up to that period, and the mean of those in 1861 for observations in that year. The first value is log $A = 0.91931$, and that for 1861 is log $A = 0.92032$. Table III. shows the unifilar observations, and the values of $X$, the horizontal component of the magnetic intensity, derived from them. Column 12 of this Table contains the dips at the several stations, and column 13 the total force $\phi = X \sec \theta$. Panama, the first station in this Table, is not included in the general assemblage of results in Table IV., its distance from the other stations being too great. Table IV. shows the combination of all observations for force to determine the direction and distance apart of the isodynamic lines. Column 3 in this Table corresponds to column 13 in Table III. We find $(x)$ the variation in total force for one mile of longitude $= +0.000925$, and $(y)$ the variation for one mile of latitude $= +0.000896$; $\frac{1}{r}$ the distance between the isodynamic lines a unit of force apart $= 776.6$ miles, or for a tenth part of a unit = 77·66 miles; \( u \), the angle which isodynamic lines make with the meridian measured from the north round by west, is 44° 6'. Column 11 of Table IV. contains the most probable value of the total force at each station, and the probable error of one such value is ±0·044. **Declination.** Table V. is similar in character to Tables II. and IV.; by it we find \((x)\) the increase of declination for one mile of longitude = +0·230, and \((y)\) the increase of declination for one mile of latitude = +0·423; \( \frac{1}{r} \) the distance between lines of equal variation 1' apart = 2·0756 miles; therefore, for 1° of difference in the declination, the distance is 124·54 miles; \( u \), the angle which lines of equal declination make with the meridian measured from the north round by west, is 61° 27'. The most probable declinations are shown in column 5 of Table V., and the probable error of one such result is ±27'. The results contained in Tables II., IV. and V. are represented graphically in Plate III., which exhibits a map of the country surveyed, with the lines of equal inclination, declination, and intensity drawn upon it. **Table I.—Dip.** | Date | Needle | Station | Poles direct | Poles reversed | Dip. | Mean dip. | |------------|--------|--------------------------|--------------|---------------|----------|-----------| | 1858. Aug. 19 | 1 | Esquimalt | 71° 18' 94" | 71° 42' 06" | 71° 30' 5" | | | 1859. Mar. 18 | 4 | | 71° 31' 55" | 71° 42' 78" | 71° 37' 2" | 71° 34' 2" | | 1860. Mar. 22 | 1 | | 71° 23' 00" | 71° 46' 20" | 71° 34' 9" | | | 1858. Oct. 4 | 1 | Sumass Prairie | 72° 12' 08" | 72° 29' 15" | 72° 20' 6" | | | | 5 | | 72° 16' 66" | 72° 29' 88" | 72° 23' 3" | 72° 22' 0" | | 1859. Jan. 31 | 4 | Nisqually | 70° 29' 62" | 70° 49' 56" | 70° 40' 0" | | | July | 4 | Schweitza Lake | 71° 57' 31" | 72° 13' 68" | 72° 05' 8" | | | | 5 | | 71° 50' 44" | 72° 13' 25" | 72° 01' 9" | 72° 03' 9" | | Sept. | 7 | Chilukwayuk Lake | 72° 19' 60" | 72° 42' 40" | 72° 31' 0" | | | 1860. May | 3 | Fort Vancouver, W. T. | 69° 02' 83" | 69° 31' 88" | 69° 17' 4" | | | | 21 | Dalles, W. T., 3-mile camp.| 69° 29' 90" | 69° 53' 80" | 69° 41' 8" | | | June | 1 | | 69° 55' 12" | 70° 13' 66" | 70° 04' 5" | | | July | 9 | 8-mile camp | 72° 29' 09" | 72° 44' 73" | 72° 36' 9" | | | August | 18 | Ashinolou Station | 72° 16' 80" | 72° 37' 20" | 72° 27' 0" | | | Nov. | 13 | Inshwolitum | 72° 34' 75" | 73° 09' 20" | 73° 48' 8" | | | 1861. March | 26 | Fort Colville | 72° 13' 51" | 73° 33' 03" | 73° 22' 0" | | | April | 4 | | 72° 44' 60" | 72° 56' 50" | 72° 50' 6" | | | | 12 | | 72° 32' 40" | 72° 44' 70" | 72° 38' 5" | 72° 41' 9" | | | 23 | | 72° 34' 20" | 72° 36' 70" | 72° 35' 5" | | | May | 19 | Chemikane River | 71° 45' 49" | 72° 24' 60" | 72° 04' 2" | | | | 31 | Sinyakwateen | 72° 29' 60" | 72° 42' 00" | 72° 35' 8" | | | | 31 | | 72° 17' 31" | 72° 50' 61" | 72° 34' 0" | 72° 34' 9" | | June | 19 | Pack River | 72° 31' 62" | 72° 59' 44" | 72° 45' 5" | | | | 23 | Chelentla | 72° 54' 56" | 73° 21' 50" | 73° 08' 0" | | | July | 6 | South Crossing (Kootenay)| 72° 37' 50" | 72° 59' 00" | 72° 48' 1" | | | | 12 | On Kootenay River | 72° 57' 31" | 73° 17' 06" | 73° 07' 2" | | | August | 19 | Tobacco Plains (Kootenay)| 73° 16' 06" | 73° 29' 44" | 73° 22' 9" | | | | 14 | Wigwam River Station | 73° 27' 06" | 73° 34' 62" | 73° 31' 0" | | | | 2 | Akamina Station | 73° 34' 12" | 73° 51' 31" | 73° 42' 7" | | ### Table II.—Dip. | Station | W. Longitude. \( \mu \) | N. Latitude. \( \lambda \) | Observed dip. \( \theta \) | Computed dip. \( \theta' \) | |-------------------------------|--------------------------|---------------------------|---------------------------|-----------------------------| | Esquimalt | 123° 27' | 48° 26' | 71° 34' | 71° 30' | | Sumass Prairie | 122° 12' | 49° 01' | 72° 22' | 72° 11' | | Nisqually | 122° 25' | 47° 07' | 70° 40' | 70° 39' | | Schweltsa Lake Station | 122° 00' | 49° 02' | 72° 04' | 72° 14' | | Chilukwayeyuk Lake | 121° 23' | 49° 02' | 72° 31' | 72° 21' | | Fort Vancouver | 122° 28' | 45° 38' | 69° 17' | 69° 28' | | Dallas, 3-mile camp | 120° 49' | 45° 35' | 69° 42' | 69° 45' | | Dallas, 8-mile camp | 120° 49' | 45° 40' | 70° 05' | 69° 49' | | On Ashpole River | 120° 00' | 49° 10' | 72° 37' | 72° 42' | | Ashtnolok Station | 120° 00' | 49° 00' | 72° 27' | 72° 34' | | Inshwoiintum Station | 118° 28' | 49° 00' | 72° 49' | 72° 50' | | Colville B. B. C. Barracks Station | 118° 05' | 48° 40' | 72° 42' | 72° 39' | | Chemikane River | 117° 45' | 48° 00' | 72° 04' | 72° 12' | | Sinayakwateen | 116° 44' | 48° 09' | 72° 35' | 72° 30' | | Pack River | 116° 28' | 48° 22' | 72° 46' | 72° 43' | | Chelemta | 116° 19' | 48° 41' | 73° 08' | 72° 59' | | South Crossing (Kootenay) | 115° 21' | 48° 22' | 72° 48' | 72° 55' | | On Kootenay River | 115° 17' | 48° 40' | 73° 07' | 73° 09' | | Tobacco Plains (Kootenay) | 115° 08' | 48° 57' | 73° 23' | 73° 24' | | Wigwam River Station | 114° 45' | 49° 00' | 73° 31' | 73° 30' | | Akamina Station | 114° 04' | 49° 01' | 73° 43' | 73° 38' | | | 393° 57' | 172° 33' | 45° 55' | |---------------------------|----------|----------|---------| \( \mu_1, \lambda_1, \text{and } \theta_1 \text{ respectively} \) ..... 118° 45' 48° 13' 72° 11' Probable error of a single observation = ±4° 93°*. * This of course includes the effects of local irregularities in terrestrial magnetism as well as actual errors of observation. A similar remark applies to Tables IV. and V. ### Table III.—Intensity of the Magnetic Force. Observations with the Unifilar Magnetometer. Vibrations and Deflections. | Date | Station | N. Latitude | W. Longitude | v₀ | log m₀ | log T₀ | log ω₀ K | log m X | log ω X | 4. | 12. | 13. | |------------|--------------------------|-------------|--------------|----|--------|--------|----------|---------|---------|----|-----|-----| | 1858, April 29 | Panama | 8° 54' | 79° 31' | 9 10 41'0 | 8 906714 | 8 906594 | 8 906594 | 8 906594 | 8 906594 | 8 906594 | 8 906594 | 8 906594 | | May | | | | | | | | | | | | | | Oct. | Tibbetts Island | 8° 46' | 79° 32' | 9 8 48'0 | 8 906594 | 8 906594 | 8 906594 | 8 906594 | 8 906594 | 8 906594 | 8 906594 | 8 906594 | | | Simmash Prairie | 49° 01' | 122° 12' | | | | | | | | | | | Nov. | | | | | | | | | | | | | | 1859, Jan. | Esquimalt Y.T. | 48° 26' | 123° 27' | 11 42'19'6 | 9 008312 | 9 008312 | 9 008312 | 9 008312 | 9 008312 | 9 008312 | 9 008312 | 9 008312 | | March | | | | | | | | | | | | | | 22 | Fort Vancouver, W.T. | 45° 38' | 122° 28' | 10 20'30'2 | 8 467000 | 8 467000 | 8 467000 | 8 467000 | 8 467000 | 8 467000 | 8 467000 | 8 467000 | | Aug. | Ashmolon Station | 49° 00' | 120° 00' | 11 52'30'4 | 9 047111 | 9 047111 | 9 047111 | 9 047111 | 9 047111 | 9 047111 | 9 047111 | 9 047111 | | 1861, April | Fort Colville | 48° 40' | 118° 05' | 11 49'49'3 | 9 045888 | 9 045888 | 9 045888 | 9 045888 | 9 045888 | 9 045888 | 9 045888 | 9 045888 | | May | Shyakvuteen | 48° 09' | 116° 44' | 11 48'39'7 | 9 043899 | 9 043899 | 9 043899 | 9 043899 | 9 043899 | 9 043899 | 9 043899 | 9 043899 | | June | Pack River | 48° 22' | 116° 28' | 11 47'17'0 | 9 042507 | 9 042507 | 9 042507 | 9 042507 | 9 042507 | 9 042507 | 9 042507 | 9 042507 | | July | South Crossing (Kootenay)| 48° 41' | 116° 19' | 11 49'22'0 | 9 041521 | 9 041521 | 9 041521 | 9 041521 | 9 041521 | 9 041521 | 9 041521 | 9 041521 | | | Cheloma River | 48° 22' | 116° 21' | 11 49'45'1 | 9 040500 | 9 040500 | 9 040500 | 9 040500 | 9 040500 | 9 040500 | 9 040500 | 9 040500 | | | Wiggan River | 49° 00' | 114° 45' | | | | | | | | | | ### Table IV.—Total Force. | Year | Station | log φ by unifilar | log φ | log \( \sqrt{\frac{\cos \gamma}{\sin u \sin w}} \) | log A. | Mean log A. | log φ | Statical φ. | Adopted φ. | φ'. | |----------|--------------------------|--------------------|-------|--------------------------------------------------|--------|-------------|-------|-------------|------------|-----| | 1859-60 | Esquimalt | 13·1097 | 1·11759 | 0·19781 | 0·91978 | 0·91931 | 1·11712 | 13·0955 | 13·103 | 13·148 | | 1858 | Sumass Prairie | 13·3727 | 1·12622 | 0·90647 | 0·91975 | 0·91931 | 1·12578 | 13·3591 | 13·366 | 13·226 | | 1859 | Nisqually | | | | | | | 13·116 | 13·111 | | | | Schwelata Lake Station | | | | | | | 13·285 | 13·285 | | | | Chilcheweyuk Lake | | | | | | | 13·294 | 13·294 | | | 1860 | Fort Vancouver | 13·0685 | 1·11589 | 0·19614 | 0·91975 | 0·91931 | 1·11545 | 13·0451 | 13·052 | 13·026 | | | Dalles, 3-mile camp | | | | | | | 13·151 | 13·087 | | | | Dalles, 8-mile camp | | | | | | | 13·003 | 13·091 | | | | On Ashnolou River | | | | | | | 13·226 | 13·315 | | | | Ashnolou Station | 13·3003 | 1·12386 | 0·20589 | 0·91797 | 0·91931 | 1·12520 | 13·3412 | 13·321 | 13·306 | | | Inshwointum Station | | | | | | | 13·272 | 13·361 | | | 1861 | Colville B. B. C. Barracks| 13·4239 | 1·12788 | 0·20584 | 0·92204 | 0·92032 | 1·12616 | 13·3709 | 13·397 | 13·357 | | | Chemikane River | | | | | | | 13·343 | 13·334 | | | | Sinyakwateen | 13·4045 | 1·12725 | 0·20471 | 0·92254 | 0·92032 | 1·12503 | 13·3361 | 13·370 | 13·238 | | | Pack River | 13·3881 | 1·12672 | 0·20660 | 0·92012 | 0·92032 | 1·12692 | 13·3944 | 13·391 | 13·401 | | | Chelemta | 13·4816 | 1·12974 | 0·20863 | 0·92111 | 0·92032 | 1·12895 | 13·4570 | 13·469 | 13·423 | | | South Crossing (Kootenay)| 13·4384 | 1·12835 | 0·20779 | 0·92056 | 0·92032 | 1·12811 | 13·4309 | 13·443 | 13·443 | | | On Kootenay River | | | | | | | 13·443 | 13·460 | | | | Tobacco Plains (Kootenay)| | | | | | | 13·443 | 13·481 | | | | Wigwam River Station | 13·4850 | 1·12985 | 0·21029 | 0·91956 | 0·92032 | 1·13061 | 13·5085 | 13·497 | 13·496 | | | Akamina Station | | | | | | | 13·587 | 13·522 | | \( \varphi_1 = 13·309 \) Probable error of a single observation \( = \pm 0·044 \) ### Table V.—Declination. | Station | W. Longitude. | N. Latitude. | Declination. | v'. | |--------------------------|---------------|--------------|--------------|-----| | Esquimalt | 123° 27' | 48° 26' | 21° 58' | 21° 20' | | Sumass Prairie | 129° 12' | 49° 01' | 21° 30' | 21° 42' | | Nisqually | 122° 25' | 47° 07' | 21° 23' | 20° 51' | | Schwelata Lake | 122° 00' | 49° 02' | 21° 37' | 21° 44' | | Fort Vancouver | 122° 28' | 45° 38' | 20° 05' | 20° 13' | | Dalles, 3-mile camp | 120° 49' | 45° 35' | 20° 37' | 20° 27' | | On Ashnolou River | 120° 00' | 49° 10' | 22° 10' | 22° 06' | | On Ashnolou River | 120° 00' | 49° 07' | 21° 50' | 22° 04' | | Ashnolou Station | 120° 00' | 49° 00' | 22° 44' | 22° 12' | | Osoyoos Station | 119° 24' | 49° 00' | 22° 14' | 22° 07' | | Inshwointum | 118° 28' | 49° 00' | 20° 17' | 22° 15' | | Colville B. B. C. Barracks| 118° 05' | 48° 40' | 21° 40' | 22° 11' | | Chemikane River | 117° 45' | 48° 00' | 21° 28' | 21° 57' | | Sinyakwateen | 116° 44' | 48° 09' | 21° 16' | 22° 10' | | Pack River | 116° 28' | 48° 22' | 22° 51' | 22° 19' | | Chelemta | 116° 19' | 48° 41' | 22° 11' | 22° 27' | | South Crossing (Kootenay)| 115° 21' | 48° 22' | 22° 16' | 22° 28' | | On Kootenay River | 115° 17' | 48° 40' | 23° 24' | 22° 36' | | Wigwam Station | 114° 45' | 49° 00' | 23° 52' | 22° 50' | | Akamina Station | 114° 04' | 49° 01' | 23° 12' | 22° 56' | 376° 01' 167° 01' 38° 35' 118° 48' 48° 21' 21° 56' Dalles, 8-mile camp.............. 120° 49' 45° 40' 18° 44' Rejected. Probable error of a single result \( = \pm 27° 06' \).