The mean of a number of determinations of serial specific gravities of sea-water taken at different times and in various parts of the world by the U. S. F. C. S. Albatross give the specific gravity reduced to 600 F. at the surface as 1.02678, at 100 fathoms as 1.02715 and at 200 fathoms as 1.02718. With these values, corrected for temperature, the weight of the column of water for the different depths was computed. The volume occupied by the air at the different depths was then computed by Boyles' law. The heat generated by the compression of the air was assumed as dissipated by the surrounding water.
The mean of the temperatures of the sea-water at 100 fathoms taken at 121 stations where serial temperatures were taken, and 174 stations where it was the bottom, a total of 295 stations gave the temperature as 50°.9 F., the air at the same time averaging 67°.4 F. and the water at the surface 64°.9 F. This giving a difference of 16°.5 F. between the temperature of the air and the sea-water at a depth of 100 fathoms.
The temperature of the sea-water at 200 fathoms taken at 89 stations where serial temperatures were taken and at 89 stations where it was the bottom, a total of 190 stations, gave the temperature as 470.7 F., the air at the same time averaging 68°.2 F and the water at the surface 67°.4 F. These temperatures and soundings were taken by the U. S. F. C. S. Albatross from 1883 to 1892 in various parts of the world. Air contracts in volume at the rate of 1/491.2 for each degree Fahr. Decrease in temperature.
This correction for contraction of volume due to change in temperature was next made. The next correction is that due to the absorption of the air under pressure, by the sea-water. The law that the weight of a gas absorbed is proportional to the pressure is not fully carried out in this case because the law is based on the assumption that the volume of gas is greatly in excess of the liquid and that the pressure is maintained until the absorption has reached its limit, neither of which conditions are
satisfied in taking soundings.
At 500.9 F water by the above law will absorb 0.01936 of its volume of air.
The result of 36 tests made with sounding tubes on the U.S. S. Prairie in July, 1900, indicates that at 100 fathoms, the absorption of the volume of air in the tube was 0.13 per cent and at 5 the absorption was 0.04 per cent. Using these two values as limits the values for other depths were easily found and these values were used for the third correction. The length of the volume of air in the tube due to pressure produced by the column of water at the various depths is as follows:
Fathoms Inches Fathoms Inches Fathoms Inches
0 24,000 22 4,495 50 2,133
5 12,020 23 4,335 52 2,057
6 10,940 24 4,180 54 1,982
7 10,060 25 4,040 56 1,915
8 9,320 26 3,904 58 1,850
9 8,658 27 3,781 60 1,785
10 8,090 28 3,661 62 1,725
11 7,590 29 3,552 64 1,671
12 7,160 30 3,441 66 1,621
13 6,770 32 3,252 68 1,573
14 6,400 34 3,088 70 1,522
15 6,078 36 2,919 75 1,420
16 5,785 38 2,779 80 1,420
17 5,520 40 2,650 85 1,251
18 5,285 42 2,530 90 1,173
19 5,070 44 2,420 95 1,112
20 4,860 46 2,320 100 1,049
21 4,670 48 2,223