APPENDIX. 335 
tow, and alfo above that, will be Co very 
fmall, chat the Difference of feveral Co- 
lumns Depth of Water will not be fenfible : 
So that an Inftrument of no greater Length 
than this, would fcarcely give an accurate 
Eftimate of half a Miles Depth, that is, 
2 <^40 Feet, or eighty Columns depth of 
Water. The lengthening therefore of this 
Inftrument to four, five, or ten times its 
length, would obviate thisDefed, and make 
the Difference of the Degrees of Defeenc 
more fenfible on the Inftrument. But fince 
it is impradicable to make a metaline Tube 
of fo great a Length, and if it were made, 
it would be fo unweildy as to be eafily bro- 
ken ; it is propofed therefore to obviate thefe 
Difficulties by the following Method, v/z, 
5. Let there be a globofe metaline Body 
be made of Copper, whofe Capacity within 
fide may be equal to nine times the Capacity 
of the metaline Tube : Let this globofe Bo- 
dy be firmly fere wed to the metaline Tube 
with a leathern Collar, well foaked in fomc 
undiious Matter, thereby to fecure that Joint 
in the moft effedual manner. 
There 
