A Table Shewing, to What Degree Air is Compressible in Sea-Water, at the Depth of Any Number of Feet from 1. to 33. Feet or 5 1/2 Fathom, and Thence for Any Number of 5 1/2 Fathoms, or 33. Feet, to 324 1/2 Fathoms or 1947 Feet

A Table showing, to what degree Air is compressible in sea-water, at the depth of any number of feet from 1 to 33 feet or 5½ fathom, and thence for any number of 5½ fathoms, or 33 feet, to 324½ fathoms or 1947 feet. Some Members of the Royal Society did with two different sorts of Instruments make divers Experiments for finding the Proportions of the Compression of Air under Water, in the Month of July, at Sheerness, in the mouth of the River of Medway, at the time of high water, where the depth was then about 19 Fathom, and the proportion of the weight of the Salt-water to that of the same quantity of Fresh water, taken out of the river Thames, was as 41 to 42. One of the Instruments was a Glass-bottle, that held a quart of water, having a brass ring fastened to the mouth of it, with a valve or flap, that open'd inward, so well fitted, that the bottle being filled more or less with water, none dropp'd out though forcibly shaken. This, let down 33 foot into the water the mouth downwards, and after a little stay drawn up, was found to be so very near half full of water, at several trials, that it was thought fit to state the Compression of Air at that depth to that measure, which at other depths was found to hold the proportions set down in the Table. The Quantity of the Compression was known by weighing the Bottle with the water in it, after that a forcible depression of the Flap had made way for the eruption of the Compressed Air (which kept it up even when the bottle was placed with the mouth upwards,) and then filling the bottle full of the same water, and weighing it again; and lastly by weighing the bottle after the water was all let forth; the weight whereof being deducted, the first quantity of water weighed just half as much as the second, or so near it that the fraction was not considerable: Whence it was concluded, that the Quantity of the Air, that filled the bottle before it was immersed in the water, was, at the depth of 33 feet, compressed into half the space it took up before, and so proportionably at other depths. This was confirm'd by repeated Experiments made with the other Instrument; which was a Cylinder of Glass, some two foot long, close at one end, and having the other end drawn drawn small with a lamp, and turn'd down a little way, after the manner expressed in Fig. 1. This Cylinder was immersed perpendicularly with the crooked end uppermost; by which, as it sunk in the water, the pressure thereof did gradually force in so much water as thrust out the Air proportionable to every depth, till the Cylinder was so far immers'd, that the hole of the crooked part of it was just 33 feet under water; and then it being drawn up, by measuring from the bottom of the Cylinder to the height of the hole in the crooked part by a pair of Compasses, the water was found to fill the Cylinder so near the half, that the motion of the superfice of the water (which then was very smooth) and the minutenes of the difference being consider'd, it was thought fit to state it to just half; according to which, confirm'd by the Trials at other depths, the ensuing Table was computed. The Proportion of the Weight of Salt-water to that of Fresh, was found by weighing some Ounces of both in a bottle whereof the weight was exactly known, and which was made with so small a neck, that the addition or diminution of one single drop in it was discernible. The Table is on these grounds computed upon the suppos'd Perpendicular immersion of a Cylinder of 60 inches, close at one end, and having the open end downwards. The first Column shews the several depths in Feet and parts of Feet. The second, in half Fathoms and whole Fathoms; a Fathom being six English feet. The third, the proportionable parts of Compression of any Quantity of Air at the several depths in the first 2 Columns. The fourth hath these proportions to a Cylinder of 60 inches, express in Inches and parts of Inches: which may easily be further calculated to any other depth desired. And that these Trials may not be thought to have been made out of meer Curiosity, they will, by considering and practical men, be found Useful for those, who have occasion to dive for recovering things lost in water, forasmuch as by those Experiments they may afore hand know, to what depth they may, when they sink in the Diving Bell or other fit Instruments, endure the Compression of the Air for respiration; as also, how they may furnish themselves with Air in a fit vessel for supply. The TABLE itself. | Depth in water | Air Comprest. | Depth in water | Air Comprest. | |---------------|---------------|---------------|---------------| | In Feet | In Fath. | to parts, to Inches | In Feet | In Fath. | to parts, to Inches | | 1 | 0 | 58\(\frac{1}{7}\) | 24 | 4 | 34\(\frac{42}{57}\) | | 2 | 0 | 56\(\frac{1}{7}\) | 25 | 0 | 34\(\frac{4}{29}\) | | 3 | \(\frac{1}{2}\) | 55 | 26 | 0 | 33\(\frac{31}{59}\) | | 4 | 0 | 53\(\frac{10}{17}\) | 27 | 4 | 33 | | 5 | 0 | 52\(\frac{2}{19}\) | 28 | 0 | 32\(\frac{28}{61}\) | | 6 | \(\frac{1}{2}\) | 50\(\frac{10}{13}\) | 29 | 0 | 31\(\frac{26}{62}\) | | 7 | 0 | 49\(\frac{1}{2}\) | 30 | 5 | 31\(\frac{1}{7}\) | | 8 | 0 | 48\(\frac{2}{41}\) | 31 | 0 | 30\(\frac{15}{64}\) | | 8\(\frac{1}{4}\) | 0 | 48 | 32 | 0 | 30\(\frac{30}{65}\) | | 9 | \(\frac{1}{2}\) | 47\(\frac{1}{7}\) | 33 | 5 | 30 | | 10 | 0 | 46\(\frac{2}{43}\) | 66 | 11 | 20 | | 11 | 0 | 45 | 99 | 16\(\frac{1}{2}\) | 15 | | 12 | 2 | 44 | 132 | 22 | 12 | | 13 | 0 | 43\(\frac{1}{3}\) | 165 | 27\(\frac{1}{2}\) | 10 | | 14 | 0 | 42\(\frac{6}{47}\) | 198 | 33 | 8\(\frac{7}{12}\) | | 15 | 2\(\frac{1}{2}\) | 41\(\frac{5}{48}\) | 231 | 38\(\frac{1}{2}\) | 7\(\frac{1}{6}\) | | 16 | 0 | 40\(\frac{10}{49}\) | 264 | 44 | 6\(\frac{1}{9}\) | | 16\(\frac{1}{2}\) | 0 | 40 | 297 | 49\(\frac{1}{2}\) | 6\(\frac{1}{10}\) | | 17 | 0 | 39\(\frac{2}{5}\) | 330 | 55 | 5\(\frac{8}{11}\) | | 18 | 3 | 38\(\frac{1}{31}\) | 363 | 60\(\frac{1}{2}\) | 5\(\frac{1}{12}\) | | 19 | 0 | 38\(\frac{1}{32}\) | 396 | 66 | 4\(\frac{8}{13}\) | | 20 | 0 | 37\(\frac{12}{53}\) | 429 | 71\(\frac{1}{2}\) | 4\(\frac{1}{14}\) | | 21 | 3\(\frac{1}{2}\) | 36\(\frac{3}{54}\) | 462 | 77 | 4\(\frac{1}{15}\) | | 22 | 0 | 36 | 495 | 82\(\frac{1}{3}\) | 3\(\frac{3}{16}\) | | 23 | 0 | 35\(\frac{5}{44}\) | 528 | 88 | 3\(\frac{2}{17}\) | Depth | Depth in water | Air Compress. | |---------------|--------------| | In Feet | In Fath. | 10 parts | Inches | | 561 | 93 | $\frac{1}{8}$ | $3\frac{1}{2}$ | | 594 | 99 | $\frac{1}{12}$ | $3\frac{3}{19}$ | | 627 | 104 | $\frac{1}{20}$ | 3 | | 660 | 110 | $\frac{1}{24}$ | $2\frac{6}{7}$ | | 693 | 115 | $\frac{1}{22}$ | $2\frac{1}{8}$ | | 726 | 121 | $\frac{1}{23}$ | $2\frac{2}{23}$ | | 759 | 126 | $\frac{1}{24}$ | $2\frac{1}{2}$ | | 792 | 132 | $\frac{1}{25}$ | $2\frac{2}{5}$ | | 825 | 137 | $\frac{1}{26}$ | $2\frac{4}{13}$ | | 858 | 143 | $\frac{1}{27}$ | $2\frac{2}{9}$ | | 891 | 148 | $\frac{1}{28}$ | $2\frac{1}{7}$ | | 924 | 154 | $\frac{1}{29}$ | $2\frac{2}{29}$ | | 957 | 159 | $\frac{1}{30}$ | 2 | | 990 | 165 | $\frac{1}{31}$ | $1\frac{29}{31}$ | | 1023 | 170 | $\frac{1}{32}$ | $1\frac{9}{16}$ | | 1056 | 176 | $\frac{1}{33}$ | $1\frac{9}{11}$ | | 1089 | 181 | $\frac{1}{34}$ | $1\frac{13}{17}$ | | 1122 | 187 | $\frac{1}{35}$ | $1\frac{5}{7}$ | | 1155 | 192 | $\frac{1}{36}$ | $1\frac{1}{3}$ | | 1188 | 198 | $\frac{1}{37}$ | $1\frac{23}{34}$ | | 1221 | 203 | $\frac{1}{38}$ | $1\frac{19}{19}$ | | 1254 | 209 | $\frac{1}{39}$ | $1\frac{7}{13}$ | | 1287 | 214 | $\frac{1}{40}$ | $1\frac{1}{2}$ | | 1320 | 220 | $\frac{1}{41}$ | $1\frac{19}{41}$ | | Depth in water | Air Compress. | |---------------|--------------| | In Feet | In Fath. | 10 parts | Inches | | 1353 | 225 | $\frac{1}{42}$ | $1\frac{3}{7}$ | | 1386 | 231 | $\frac{1}{43}$ | $1\frac{1}{43}$ | | 1419 | 236 | $\frac{1}{44}$ | $1\frac{1}{11}$ | | 1452 | 242 | $\frac{1}{45}$ | $1\frac{1}{45}$ | | 1485 | 247 | $\frac{1}{46}$ | $1\frac{1}{46}$ | | 1518 | 253 | $\frac{1}{47}$ | $1\frac{1}{47}$ | | 1551 | 258 | $\frac{1}{48}$ | $1\frac{1}{48}$ | | 1584 | 264 | $\frac{1}{49}$ | $1\frac{1}{49}$ | | 1617 | 269 | $\frac{1}{50}$ | $1\frac{1}{50}$ | | 1650 | 275 | $\frac{1}{51}$ | $1\frac{1}{51}$ | | 1683 | 280 | $\frac{1}{52}$ | $1\frac{1}{52}$ | | 1716 | 286 | $\frac{1}{53}$ | $1\frac{1}{53}$ | | 1749 | 291 | $\frac{1}{54}$ | $1\frac{1}{54}$ | | 1782 | 297 | $\frac{1}{55}$ | $1\frac{1}{55}$ | | 1815 | 302 | $\frac{1}{56}$ | $1\frac{1}{56}$ | | 1848 | 308 | $\frac{1}{57}$ | $1\frac{1}{57}$ | | 1881 | 313 | $\frac{1}{58}$ | $1\frac{1}{58}$ | | 1914 | 319 | $\frac{1}{59}$ | $1\frac{1}{59}$ | | 1947 | 324 | $\frac{1}{60}$ | $1$ | Extracts