114 JAMES CLERK MAXWELL 



ture as thus defined by Herapath is an absolute 

 temperature, and he calculates the absolute zero of 

 temperature at which the gas would have no volume 

 from the above results. The actual calculation is of 

 course wrong, for, as we know now by experiment, the 

 pressure is proportional to the temperature, and not 

 to its square, as Herapath supposed. It will be seen, 

 however, that Herapath's formula gives Boyle's law: 

 for if the temperature is constant, the formula is 

 equivalent to 



I* V = a constant. 



Herapath somewhat extended his work in his 

 "Mathematical Physics" published in 1847, and 

 applied his principles to explain diffusion, the relation 

 between specific heat and atomic weight, and other 

 properties of bodies, lie still, however, retained his 

 erroneous supposition that temperature is to be 

 measured by the momentum of the individual 

 particles. 



The next step in the theory was made by 

 Waterston. His paper was read to the Royal Society 

 on March 5th, LS4G*. It was most unfortunately 

 committed to the Archives of the Society, and was 

 only disinterred by Lord Kayleigh in IS02 and 

 printed in the Transactions for that year. 



In the account just given of the theory, it has 

 been supposed that all the particles move with the 

 same velocity. This is clearly not the case in a gas. 

 If at starting all the particles had the same velocity, 

 the collisions would change this state of affairs. Some 

 particles will be moving quickly, some slowly. \Ve may, 



