336 APPENDIX. 
6 . There mufl: be a Hole at the^ Bottorri 
of the Copper glob Opening into a me** 
taline Tube foddered to that Hole, which 
Tube muft be three or four Inches length, 
that it may be immerfed in a proper meca- 
line Ciftern, full of fotne tinged unduous 
Matter, as Oil, or the like, which being fpe- 
cifically lighter than Sea Water, will fwim 
upon it, and confequently will daub the in- 
fide of the Iron Tube, as far as the Water 
was impelled up it^ And in order to know 
that Height, there mufl: be fixed a flender 
Rod of Brafs, Iron or Wood, in the middle 
of the Iron Tube from End to End, with a 
Knob at its upper End, both to keep it at 
that End in the middle of the Tube, and 
alfo to prevent its being befmeared by the 
fides of the Tube, when it is drawn out to 
fee by the Mark of the unduous Matter on 
the Rod to what Height the Water had been 
preiTed up the Tube. 
7 . The Capacity of the Tube muft be 
eflimated by pouring Water in, when the 
Rod and metaline Diameter are fixed in their 
Places. 
8 . Now fince the Copper Globe is fup- 
pofed to contain nine times as much Air as 
the 
