Manchester AIe})wirs, Vol. Iv. ( 1 9 1 1 ), No. 5. 1 3. 



Dalton came under the stimulus of Newton's atomic 

 theory. Everything goes to show that this had a great 

 effect on him. He hardly mentions Newton in his 

 early writings. In 1801, and subsequently, he quoted 

 Newton on every suitable occasion, and in particular he 

 mentions the 23rd Proposition of the 2nd Book of the 

 " i'rincipia " at least five times. The mutually repulsive 

 particles of this proposition play their part in Dalton's 

 theory. The wording of it shows this : — " When two 

 elastic fluids, denoted by A and B are mixed together^ 

 there is no mutual repulsion amongst their particles ;, 

 that is the particles of A do not repel those of B, as they 

 do one another." ^° 



Dalton's theory is a true development of the theory 

 of Newton, in respect that it is a static one, representing 

 the atoms as being, ultimately, at rest among themselves. 

 If, as was shown in the 3rd paper of this series, Newton, 

 in forming his theory deliberately set aside the dynamic 

 ideas of Descartes, it is to be remembered that these 

 ideas at length found expression in the Kinetic Theory of 

 Gases. 



The amended diffusion hypotliesis. 



As already stated in the second paper of this series, 

 Dalton explained in a lecture which he gave in 18 10, that 

 he had not at first contemplated the effect o{ difference of 

 size in the particles of elastic fluids. But he reflected that 

 if the sizes be different, then on the supposition that the 

 repulsive power is heat, no equilibrium can be established 

 by particles of different sizes pressing against each other." 

 On consideration, he found "that the sizes must be 

 different ; " " thus," he concludes, " we arrive at the reason 

 for that diffusion of every gas through every other gas, 



-" Manchcsier i]Ieiiioirs, [l], vol. 5, p. 536, l8o2. 



