Manchester Memoirs, Vol. Iv. (1910), No. 4- 7 



Newton proved that the air must obey Boyle's law, 

 if the force of repulsion between its particles were in- 

 versely proportional to the distance between them. He 

 does not mention Boyle, or the air, but puts the matter in 

 the most abstract way, by advancing the following propo- 

 sition : — " If the density of a fluid which is made up of 

 mutually repulsive particles, is proportional to the pressure, 

 the forces between the particles are reciprocally propor- 

 tional to the distance between their centres. And vice 

 versa, mutually repulsive particles, the forces between 

 which are reciprocally proportional to the distance between 

 their centres, will make up an elastic fluid, the density 

 of which is proportional to the pressure." ^^ 



Newton does not draw any inference as to the nature 

 of the atmosphere. " All these things are to be under- 

 stood of particles whose centrifugal forces terminate in 

 those particles that are next them, or are diffused not 

 much further. We have an example of this in magnetical 

 bodies. .... Whether elastic fluids do really consist of 

 particles so repelling each other, is a physical question. 

 We have here demonstrated mathematically the property 

 of fluids consisting of particles of this kind, that hence 

 philosophers may take occasion to discuss that question." 



This proposition, along with its proof in the " Principia,'' 

 is the earliest instance of the mathematical treatment of 

 the atomic theory. Svante Arrhenius declares that "the 

 atomic theory remained in the hypothetical state for 

 about 2,300 years, as no quantitative conclusions were 

 drawn from it till the time of Dalton." '" This statement 

 entirely ignores Newton's explanation of Boyle's law in 

 terms of atoms, as well as certain workers in the 

 eighteenth century, who were under Newton's influence. 



^'^ " Principia," Book 2, prop. 23. 



^^ Arrhenius, " Theoi'ies of Chemistry, Eng. trans., p. 15. 



