552 On the Force of Steam or Vapcur 
progress of philosophy is more immediately in 
terested in accurate observations on the force of 
steam in low temperatures. Different authors 
have published accounts of their experiments 
on the force of steam: I have ona former occa- 
sion (Meteorological Essays, page 134) given a 
table of forces for every 10° from 80° to 212% 
The author of the article ‘* Steam” in the’ En- 
cyclopedia Britannica, has: done the-same from 
32° to 280°: and M. Betancourt, in the ‘* Me- 
moirs des jscavans etrangeres” for 1790, (see 
Hutton’s Math, Diction. page 755) has’ given 
tables 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 nothing, 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 ; 
owing as I apprehend to a quantity of air, which 
being disengaged from the water by heat and 
mixing withthe 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 
