i iB Count Rumford’s Enquiry concerning the Nature of Heat , 
and it is evident, that the distance to which the bubble is driven 
out of its place, must necessarily be greater or less, in propor- 
tion as that difference is greater or less. 
In those experiments in which the horizontal cylindrical 
vessels were filled with hot water, and then presented to the 
balls of the instrument, the temperature of the circular flat sur- 
faces was that of i8o°, while the temperature of the air of the 
room in which those experiments were made, and consequently 
that of the balls, was about 6o°; the difference amounts to no less 
than 120 degrees of Fahrenheit’s scale; but, in these experi- 
ments with cold, the difference of the temperatures at the moment 
when the cold bodies were first presented to the instrument, did 
not probably amount to more than 40, or at the most 50 de- 
grees ; and, in a very few seconds, it must have been reduced 
to less than 30 degrees, in consequence of the freezing of the 
water precipitated by the air of the atmosphere, on the surface 
of the vessel containing the cold mixture. 
This precipitation of water, by the surrounding air, was so 
copious, that the brilliancy of the polish of the metallic surface 
was almost instantly obscured by it ; and the vessels were 
very soon covered with a thick coat of ice. These accidents, 
which were not to be prevented, affected in a very sensible 
manner the results of the experiment. The bubble, instead of 
remaining stationary for some time after it had reached the 
point of its greatest elongation, as it had done in the experi- 
ments with' hot bodies, had no sooner reached that point, than it 
began to return back towards the place from which it had set 
out ; and, as often as I wiped off the ice from the surface of the 
flat end of the vessel which was not blackened, and presented it 
clean and bright to the ball of the instrument, the bubble began 
