CALORIC. 25 



the state of vapour or gas^ and the water is 

 changed into an aeriform fluid. 



The same may be affirmed of all bodies in na- 

 ture. They are either solid, or liquid, or in the 

 state of elastic aeriform vapour, according to the 

 proportion which takes place between the attrac- 

 tive force inherent in their particles, and the re- 

 pulsive power of heat acting on them ; or, what 

 amounts to the same thing, in proportion to the 

 degrees of heat to which they are exposed. But 

 were there no other cause affecting the solidity of 

 bodies except the powers of attraction and repul- 

 sion, they would become liquid at an indivisible 

 degree of the thermometer, and would almost in- 

 stantaneously pass from the solid state of aggreg- 

 ation to that of aeriform elasticity. Thus water, 

 for instance, at the very instant when it ceases to 

 be ice, would begin to boil, and would be trans- 

 formed into an aeriform fluid, having its particles 

 scattered indefinitely through the surrounding 

 space. That this does not happen, must depend 

 upon the action of some third power. The pres- 

 sure of the atmosphere prevents this separation, 

 and causes the water to remain in the liquid state 

 until raised to the temperature indicated by SIS'^ ; 

 the quantities of caloric, which it receives in the 

 lower temperatures, being insufficient to overcome 

 the pressure of the atmosphere. 



Whence it appears, that, without this atmos- 

 pheric pressure, we should not have any permanent 

 liquid, and should only see bodies in that state in 

 the very instant of melting ; for the smallest addi- 

 tion of caloric would then instantly separate the 

 particles, and dissipate them through the surround 

 ing medium. Besides, without this atmospheric 

 pressure, we should not even have any proper aeri- 



