Prof. Green’s a 165 
ed to contain the air and sais with the bottom open so 
as to slide easily between the inner and the outer cylinders. 
‘ a small quantity of water being added to 
fill up the space between them ; round the bottom of C. C, 
isa rim of lead to sink the vessel i in the water and compress 
the enclosed air, and on the top there is a stop cock F. 
From another stop cock G. on outside of A. A. there 
runs a tube down under the apparatus and os rising through 
the interior cylinder B. B. and its top at H. (the opening 
by which it passes being soldered so as to be air tight.) On 
the outer part of the stop-cock G. is cut a screw, to which 
can be applied the caps I. I. I. Fi igure 2, when apertures 
of various sizes are wanted. 
o use the aoa § the cylindrical vessel C. C. is ta- 
ken out from between A. A. and B. B. and the stop-cock 
F. shut ; anda ‘ddicient quantity of water poured between 
the outer and inner cylinders. C.C. is then adjusted in its 
place, the cock G. being closed. The vessel C. C. decends 
by reason of its gravity and the atmospheric air is forced by 
the pressure through the opening H. down the tube H. K. 
and out of the orifice G. where the stop-cock G. is opened, 
thus a continued and uniform jet of air may be thrown on 
the flame of a lamp placed before G... The caps I. I. I. are 
about half an inch have a female screw at one end to fit on 
G. and are perforated with different apertures at the other 
end to regulate the jet of air. When theair in the sear 
isexhausted or when it has descended as far as ib 
genious siaib sitet al instrument inaleet at Boston has used 
it with success for some time. 
By a little additional apparatus it can be used asa gasom- 
eter, by means of ieek the cylinder C. C. may be filled 
with oxygen or any other gas; in this case C. must be sus- 
ed by cords over pulleys and counterpoised by a 
weight. will be unnecessary to go into a description of the 
