7i2 Col. roy’s Experiments far 
exceed that deduced from the operations of the barome- 
ter in extreme temperatures; yet they agree exceedingly 
well with each other for the mean heat of the air, when 
the barometer will come moft frequently into ufe. 
The fourth clafs of experiments are all that now re- 
main to be mentioned. The bare infpedfion of table. 
iv. will fhew r how greatly fuperior the elaftic force of 
moift is to that of dry air. It is true indeed, that two 
kinds of irregularities prefent themfelves among the re- 
fults: firft, with regard to the total expanlion for 212’; 
and fecondly, as to the greateft exertion of the elafiic 
force, which fometimes feems to have taken place before 
the air has acquired the heat of boiling water. The 
firft is eafily accounted for : it muft have arifen from dif- 
ferent proportions of moifture being admitted into the 
fame quantity of air, which there was no pofiibility of 
afeertaining, the bulbs and their apertures being of very 
different dimenfions. With regard to the fecond irregu- 
larity, I am rather inclined to think that it may have 
proceeded from error of obfervation, it being difficult to 
determine the accurate temperature near boiling; efpe- 
cially when any part of the air rofe above the top of the 
veffel, which was fometimes the cafe, notwithftanding its 
extraordinary height. Be that as it may, a very uniform 
encreafing progreffion will be perceived to take place, 
from 
