Steam JEnp'ine, 5S 
ton^s Math. Diction, page 755) has gi^'en ta!:>ies on the 
subject, both for vapour from water and spirit of wine, 
also from 32^ to 280^, But these two authors, having 
assumed the force of vapour from water of 32° to be no- 
thing, are essentially wrong at that point and in all the 
lower parts of the scale ; and in the higher part, or that 
above 212°, they determine the force too much: owine’ 
as I apprehend to a quantity of air, w^hich being disenga- 
ged from the w/ater by heat and mixing with the steam, 
increases the elasticity. — In a question of such moment 
it seemed therefore desirable to obtain greater accuracy. 
My method is this : I take a barometer tube perfectly 
dry, and fill it with mercury just boiled, marking the place 
where it is stationary ; then having graduated the tube 
into inches and tenths by means of a file, I pour a little 
water (or any 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, ex- 
clude all air : the barometer by standing some time exhi- 
bits 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 ; tvhich 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, perfora- 
ted in the middle so as to admit the barometer tube to be 
pushed through and to be held fiist by them ; the upper 
cork is fixed two or three inches belotv the top of the tube, 
and is half cut away so as to admit water, &c. to pass 
by ; its service being merely to keep the tube steady. 
Things being thus circumstanced, water of any tempera- 
ture may be poured into the wdde tube, and thus made 
to surround the upper part or vaepum of the barometer, 
and the effect of temperature in the production of vapour 
