2,60 Dr. ingenhousz on Air , 
rife of the water nearly the fame, though not fo exactly 
as I could have wifhed : the variation I afcribed partly 
to the elaftic bottle not being always of the fame firmnefs 
or elafticity, which it lofes more or lels by fqueezing. I 
contrived another method more fimple, and perhaps more 
accurate, which is the following : I took a glafs tube about 
two and a half feet long, and not quite a twelfth of an inch 
in diameter; fo that a column of quickfilver might llide 
through the whole without difperfing itfelf, filling al- 
ways the whole cavity. I cemented to each extremity a 
brafs ring, that I might be able to lhut the opening with 
my finger without hurting myfelf. This tube being di- 
vided into i oo equal parts, I riled it in two different ways ; 
viz. having poured fome aquafortis into a little phial, and 
put to it fome filings, I thruft the extremity of the glafs 
tube, into the neck of the phial. A column of quickfil- 
ver of about an inch in length occupied that end of the 
glafs tube which was in the neck of the phial. The 
whole was kept in fuch a pofture that the tube was nearly 
in an horizontal line, the end which is put into the phial 
being rather the highefi. Care was taken that the tube 
fhould not touch the aquafortis. The phial being filled 
with red fumes and the extremity of the tube furrounded 
with them, I open and lhut alternately the oppofite extre- 
mity of the tube, fo as to allow the quickfilver to advance 
flowly towards the middle ; as foon as the column of quick- 
filver is arrived at the middle, I take the tube out of the 
bottle, and fhut each extremity with the fore-finger: thus 
moving the tube upwards and downwards as brifkly as 
can be done with a certainty of keeping both extremities- 
all 
