APPENDIX. 333 
1 . Suppofe there be an Iron or Copper 
Tube, or a Musket Barrel of any Length, as 
fifty Inches, having its upper end well 
clofed up : If this Tube be let down, in this 
Pofition, about thirty three Feet in the Sea, 
for a Column of Sea Water of that Height 
is nearly equal to the middle Weight of our 
Atmofphere 5 then confequently from a known 
Property of the Air’s Elafticity, it will be 
comprefled into half the Space it took up 
before, fo that the Water will afcend half 
way up the Tube, and if the Tube be let 
down thirty three Feet deeper, the Air will 
be comprefled into one Third of its firft Di- 
menfion, and fo on ;^th, fth, |th, The 
Air being conftantly compreflible in Propor- 
tion to the incumbent Weight ; whence by 
knowing to what Height the Water has af. 
cended in the Tube, we may readily know 
to' what Depth the Tube has defcended in 
the Sea. 
3. Now to meafure the Depth of one of 
thefe Columns of Sea Water, whofe fpecific 
Gravity to pump Water is found to be as 
forty one to forty. Firft by a Line let the 
Iron Tube, with a Weight at its Bottom, 
fmk about thirty three Feet, which Depth in 
Salt 
