[ 179 ] 
Thefe obfervatlons and experiments feem to difco- 
ver to us fully the nature of thofe bubbles that 
afcend through boiling water. And from hence I 
think we may learn the reafon why any fluid, in an 
open veffel, will acquire only a certain degree of 
heat when it boils, and will not grow hotter after- 
wards?; and why different fluids will acquire different 
degrees of heat in boiling ? The parts of the fluid 
neareff the bottom grow hot at firff, and being then 
expanded and made lighter, they afcend and change 
place with the colder and heavier parts ( which 
occajions that intejiine motion we perceive m liquors 
while they are growing hot) ; and thus the heat 
of the whole will increafe, until thofe particles, 
that are in contact with the bottom of the veffel, 
acquire fuch a degree of heat as will give them 
a repelling force able to overcome the weight 
of the atmofphere, the weight of the incumbent 
fluid, and the tenacity of its particles; and then 
they be fuddenly expanded into bubbles of 
fteara, and afcend quickly to the top, without com- 
municating this heat to the furrounding fluid: for 
as thefe bubbles have a degree of heat but little fu- 
perior to that of the fluid, and jufl fuffleient to keep 
them expanded, if they were to lofe this heat, by 
communicating it to the fluid in their afeent, they 
would all difappear before they got to the furface ; 
or if the whole fluid was to grow as hot as the bub- 
bles, it would, like them, be all turned into elaflic 
fleam ; and, therefore, the fluid itfelf cannot grow 
hotter than when thefe bubbles began to afcend. 
That thefe bubbles are really hotter than the other 
parts of the fluid I found by the following experi- 
A a 2 ment. 
