346 APPENDIX. 
If wc fuppofe that the whole Quantity of 
Earth, which is above the level of the Sur- 
face of the Seas, were equal to the whole 
Bulk of the Waters in the Bafin of the Seas ; 
then lince the Sum of the Expanfe of all the 
Seas is confiderably more than the Sum of 
the Surface of all the Earth on this Globe, 
the general Depth of the Sea muft there- 
fore be confiderably lefs, than the general 
Height of the Earth above the Surface of 
the Sea. 
24. To this Method of taking the Depth 
of the Sea it may reafonably be objcfted, 
that though it has been found by Experience 
that in leffer Degrees the Air is compreflible 
in Proportion to the incumbent Weights; 
yet it is to be feared that in greater Degrees of 
Comprefllire, this proportional Compreffibi- 
lity would not hold true, by reafon of the 
many watry and other heterogeneous Mix- 
tures in the Air, which would hinder its 
equable Compreffibility. Yet fince the irre- 
gular Degrees of its Compreffibility are noc 
yet certainly known, it might be well to try 
the Inllrumcnt fiift to the greateft Depth a 
Line can be let down, which I find has been 
to four hundred Fathom, in which cafe the 
Air 
( 
