78 W. A. Norton on Molecular Physics. 
In the process of ebullition, the expansive action of the heat 
absorbed by the lower layers of the liquid increases until the 
superincumbent pressure, the cohesive attraction of the vessel: 
for the liquid, and the effective attractions subsisting between 
the molecules of the liquid (represented by the ordinates be- 
tween a and 4, fig. 1), are overcome. When this point is reached 
at any part of the liquid stratum, the separated particles will 
expand rapidly into bubbles of vapor, in opposition to the 
pressure of the atmosphere, and the attractions denoted by the 
decreasing ordinates between } and «¢, fig. 1. The expansion 
should continue until the distance between the atmospheres o 
[To be continued] 
