404 On the Velocity of Air. 
Description of the Instrument, ec. 
ee RE 
The metal box or tube B, may be about the 
size of the figure; the top must be made air 
tight by the cover L; into the bottom is fixed 
the small tube. AC, and into the piece D is 
cemented the glass tube ED; the instrument 
is then inverted, and some water poured through 
the tube AC, till when in its proper position it 
is visible at D. It is now ready for use, and the 
end A may be fixedin a hole 1 nade in the upper 
board of the bellows, and the water will rise in 
the glass tube, in smiths’ bellows generally from 
9 to 12 inches, furnace bellows generally 4 feet or 
more. But where the fa Boe is great, 
quicksilver may be use d instead of water, only in 
this case’ the instrupen ts ould be made of iron, 
causes the screws of brass to break. 
a uicksil ver, the tube ED may be 
length of 12 or 
i be eno igh for any blast. The glass 
st be more than one eighth or one 
as quicksilve 
Rint Ree 
Or, instead o 
enth of an inch in diameter. 
- ieee ris eae ia ee : : j 
Whatever compression there may be in the 
bellows there will be the same in the upper part 
