54 
Steam Engine, 
‘‘ same for the same variation of temperature^ reckoning 
from vapour of any given force: thus, assuming a force 
“ equal to thirty inches of mercury as the standard, it be- 
ing the force of vapour from any liquid boiling in the 
open air, vre find aqeous vapour loses half its force by a 
diminution of 30 degrees of temperature : so does the 
vapour of any other liquid lose half its force by dimi- 
nishing its temperature 30 degrees below that in which 
“ it boils ; and the like for any other increment or decre- 
“ ment of heat. This being the case, it becomes unneces- 
sary to give distinct tables of the force of vapour from 
different liquids, as one and the same table is sufficient 
for all.” 
The experiments on which this conclusion rests, are re« 
fated in the fifth volume of the Manchester Memoirs: they 
may also be seen in the 6th volume of the New Series of 
Mr, Nicholson"* s Journal, Mr. Dalton has calculated a 
table of the force of vapour of water from the temperature 
of 40^ below zero of Fahrenheit, to 325^ above it. From 
this table we have extracted the following ; in which we 
have, as before, reduced the force to the medium pressure 
of the atmosphere for the measuring unit, that the small 
differences in the results of the English and the Spanish 
philosopher may be the more readily traced.. 
