Letter from the late Mr. Ivory on Dalton^s Theory, 55 

 Before diffusion. After diffusion. 



After diffusion the dissimilar particles have obviously on the 

 whole approached each other, and the similar ones receded 

 from each other ; what is true of two atoms is true of any 

 number. 



It is curious that the same mathematical formula by which 

 I expressed the conditions of the question on the inelastic hy- 

 pothesis are equally applicable to the attractive theory. 



It is an instance of Newton's third law of motion, that action 

 and reaction are equal, and the very same formula applies to 

 attractive as to repulsive forces, simply by the change of sign 

 {pljis or minus) + or — . 



There are many collateral applications of this idea, for 

 the explanation of which I shall at some future period again 

 seek the medium of your valuable Journal. In conclusion, I 

 present you for publication two letters connected with this 

 subject, addressed to me by the late James Ivoi'y, Esq., and 

 subscribe myself, Dear Sir, 



Your sincerely obliged friend, 

 London, June 11, 1844. Thos. S. ThOMSON. 



" 121 Camden Road Villas, Camden Town, 

 « My dear Sir, February 21, 1842. 



" I am much gratified by your letter. I have only added 

 to Dalton's theory what is necessary to reduce it to correct 

 physical principles. In the next Magazine in the press, you 

 will find that I have applied the theory as I have explained it, 

 to determine the composition of atmospheric air; that is, I have 

 demonstrated as a consequence of the theory that a volume of 

 air consists of 21 parts of oxygen and 74 of azote. In the 

 Magazine for April I propose to continue the subject, chiefly 

 to explain the manner in which aqueous vapour exists in the 

 atmosphere, which comes under the same theory. 



" I shall be very glad to have the perusal of your specula- 

 tions. " Believe me to be, 

 " To Thos. S. Thomson, Esq., " Respectfully, yours, &c., 

 5 Burt/ St., St. James's." " James Ivory." 



