68 
Steam Engine, 
212® : the vapour from ether depresses the mercury about 
six inches in the temperature of 32 degrees. 
Finding that ether belozv the point of ebullition agreed 
with water below the said point, I naturally concluded 
that ether above the point would give the same force of 
vapour as water above it ; and in this I was not disap- 
pointed ; for, upon trial it appeared that what I had infer- 
red only from analogical reasoning respecting the force of 
aqueous vapour above the boiling point, actually happen- 
ed with that from ether above the said point. And ether 
is a much better subject for experiment in this case than 
water, because it does not require so high a temperature. 
I took a barometer tube of 45 inches in length, and 
having sealed it hermetically at one end, bent it into a sy- 
phon shape, making the legs parallel, the one that was 
close being nine inches long, and the other thirty-six. 
Then conveyed two or three drops of ether to the end of 
the closed leg, and hlled the rest of the tube with mercu- 
ry, except about ten inches at the open end. This done, 
I immersed the whole of the short leg containing the ether 
into a tail glass containing hot water; the ether thus ex- 
posed to a heat above the temperature at which it boils, 
produced a vapour more powerful tlian the atmosphere, 
so as to overcome its pressure and raise a column of mer- 
cury besides, of greater or less length according to the 
temperature of the water. When the water was at 147 
the vapour raised a column of 35 inches of mercury, when 
the atmospheric pressure was 29.75 : so that vapour from 
ether of 147 degrees is equivalent to a pressure of 64.75 
inches of mercury ; agreeing with the force of aqueous 
vapour of 257 degrees, according to the preceding estima- 
tion : in both cases the temperatures are 45 degrees above 
the respective points of ebiiliition. In all the temperatures 
betwixt 102 degrees and 147 degrees the forces of ethe- 
real vapour corresponded with tliose of aqueous vapour. 
