from Water and other Liquids, Sc. 53 
other liquid the subject. of experiment) into it, 
so as to moisten the whole inside; after this I 
again pour in mercury, and, carefully inverting 
the tube, exclude all air: the barometer by 
Standing. some time exhibits a portion of water, 
&c, of or of an inch upon the top of the 
mercurial column; because being lighter it as- 
cends by the side of the tube; which may now 
be inclined and the mercury will rise to the top 
manifesting a perfect vacuum from air. I next 
take a cylindrical glass tube open at both ends, 
of 2 inches diameter and 14 inches in length; to 
each end of which a cork is adapted, perforated 
in the middle so as to admit the barometer tube 
to be pushed through and to be heid fast by them; 
the upper cork is fixed two or three inches below 
the top of the tube and is 2 cut away soas to 
admit water, &c. to pass by; its service being 
merely to keep the tube steady, ‘Things being 
thus circumstanced, water of any temperature 
may be poured into the wide tube, and thus 
made to surround the upper part or vacuum of 
the barometer, and the effect of temperature in 
the production of vapour within can be observed 
from the depression of the mercurial column. 
In this way I have had water as high as 155° 
surrounding. the vacuum: butas the higher tem- 
peratures might endanger a glass apparatus; 
jnstead of it I used the following :— 
