164 ESSAYS anp OBSERVATIONS. 
finking of the thermometer. produced by 
each, .For this purpofe, it would be necef- 
fary to repeat the trials often and with pre- 
cifely the fame circumftances at each time: 
“Which I find to be very difficult. In the 
mean time I have endeavoured to give a 
notion of the comparative power of thefe 
fluids in producing cold, by the order in 
which I have fec them down; having men- — 
‘tioned that fluid firft which feemed to me 
to occafion the greateit finking of the ther- 
moméeter, and the reft follow in order as 
they feemed to occafion lefs and lefs. 
From the above enumeration I ima- 
gine it will appear, that the power of eva- 
porating fluids in producing cold, is near- 
ly according to the degree of volatility in 
each. If to this we join the confideration, 
that the cold is made greater by whatever 
haftens the evaporation, and particularly, 
that the finking of the thermometer is 
greater as the air in which the experiment 
is made is warmer, if dry at the fame time ; 
I think we may now conclude, that the 
cold produced is the effect of evaporation. 
