340 APPENDIX. 
fice inverted downwards, the Air in them 
will be eomprefled to fuch a Degree, at great 
Depths, as thereby to make the buoyant Bo- 
dy become fpedfically heavier than the Sea- 
Water, which would prevent its reafeending 
to the Surface of the Sea j for which reafon 
alfo the Buoy ought to be able to buoy up 
the Inftrument when full of Water. Befides, 
if the Buoy when it rifes again do not ap- 
pear fome confiderable Height above the 
Water, it will not eafily be difeovered : For 
it is probable, that from great Depths it may 
rife at a confiderable didance from the Ship 
though in a Calm. To make the Buoy there- 
fore the more vifiblc at a Diftance, it will be 
proper to fix acrofs each other, at the Top 
of the Buoy, broad Fans of Tin, painted ei- 
ther black or white, as (hall be found mofl: 
convenient. 
ij. For greater Accuracy, it will be need- 
ful firft to try this Sea-Gage, at feveral dif- 
ferent Depths, down to the greateft Depth 
that a Line can reach, thereby to difeover, 
whether or how much the Spring of the 
Air is difturbed or condenfed, not only by 
the great Prefiure of the incumbent Water, 
but alfo by its Degrees of Warmth or Cold- 
nc(s 
