334 ~AP P E N D 1 X. 
Sale Water will nearly anfwer to the Weighc 
of the Air, at a mean Height of the Baro- 
meter, then draw up the Tube and obfervd 
how far the Water rofe 5 if thirty three Feet 
of Water is equal to one Atmofphere, then 
will the Water rife fo high as to fill exaftly 
one half of the Tube : But if the Water rifes 
higher or lower than half way, then by the 
Rule of Three fay, as the Number to which 
the Water rifes is to one, fo is thirty three 
to the Number of Feet, meafuring the Depth 
of the Column required. For Example^ 
fuppofe the Water rifes (when the Tube is 
let down thirty three Feet) only nine Tenths 
of half way, then fay as 5) : lo : : 53 : 3 Feet 
the Depth of each Column, which being 
once known, the Number of Columns of 
Water is to be multiplied by this Number of 
Feet, whereby the Depth of the Sea in Feet 
will be known. 
4. But fince when the Inftrument has de- 
feended to the Depth of ninety nine Co- 
lumns, or ninety nine times thirty three 
Feet, the Air will be comprefled into the 
TT^th Part of fifty Inches, that is, half an 
Inch, the Divifions both for fome Space be- 
I0W3 
