Mf. Cavendish' s Experiments on Air, 
be tried was then introduced by means of a fmall tube, fuch as 
is ufed for thermometers, bent in the' manner reprefented by- 
ABC (fig. 2.) the bent end of which, after being previoufly 
filled with quickfilver, was introduced, as in the figure, under 
the glafs DEF, inverted into water, and filled with the proper 
kind of air, the end C of the tube being kept flopped by the 
finger; then, on removing the finger from C, the quickfilver 
in the tube defcended in the leg BC, and its place was fupplied 
with air from the glafs DEF. Having thus got the proper 
quantity of air into the tube ABC, it was held with the end C 
uppermofl, and flopped with the finger ; and the end A, made 
fr&aller for that purpofe, being introduced into one end of the 
bent tube M, (fig, i .) the air, on removing the finger from C, 
was forced into that tube by the prefliire of the quickfilver in 
the leg BC. By thefe means I was enabled to introduce the 
exadl quantity I pleafed of any kind of air into the tube M ; 
" and, by the fame means, I could let up any quantity of foap° - 
lees, or any other liquor which I wanted to be in contafl with 
the air. 
In one cafe, however, in which I wanted to introduce air 
into the tube many times in the fame experiment, I ufed the 
apparatus reprefented in fig. 3. confiffing of a tube AB of a 
fmall bore, a ball C, and a tube DE of a larger bore. This 
apparatus was firfl filled with quickfilver ; and then the ball 
C, and the tube AB, were filled with air, by introducing the 
end A under a glafs inverted into water, which contained the 
proper kind of air, and drawing out the quickfilver from the 
leg ED by a fyphon. After being thus furnifhed with air, the 
apparatus was weighed, and the end A introduced into one end 
of the tube M, and kept there during the experiment ; the 
way of forcing air out of this apparatus into the tube being by 
thrulMng 
