242 Remarks on a Paper ly Mr. Dalton 



our atmosphere consisted of a mixture of oxygen and azote. Sir 

 H. Davy considered the constituents of the atmosphere as che- 

 mical! v united ; and his reasons for supposing so are adduced, hut 

 must be rc4inquishcd a:s ill founded, &:c." 



Mr. Dalton next alludes lo his Essays on the Constitution of 

 mixed Gases, published in 1802; containing an hypothesis to 

 explain the uniform diffusion of gases by mechanical means. Ou 

 this principle, the atmosphere was considered a mixture not a 

 combination of its elements. 



Before I proceed any further with Mr. Dalton's paper, I will 

 in a few words mention the prominent features of his hypothesis. 

 He sup])oses that one gas affords a vacuum in its interstices for 

 a second gas of a different nature from itself, and that each par- 

 ticle of the same gas in the mixture presses only on its kindred 

 particle ; so that the pressure of each of the different gases which 

 constitute our atmosphere is independent of the other ; not one 

 of them pressing on the other, but all distinctly with one uniform 

 weight rest on the surface of the earth. The same law holds 

 good as to the mixture of other gases. 



This is a strange hypothesis, which one cannot well reconcile 

 to common sense. All kinds of gases mix uniformly, and there 

 are many gases whose ultimate divisions are of the same size, 

 and some gases whose ultimate particles are much smaller than 

 others ; yet their atmosjjheres of caloric are often larger. The 

 calorific atmospheres of hydrogen are larger than those of oxygen. 

 There are some gases whose atmospheres are of the same size; — 

 how then can all gases indiscriminately afford vacant interstices 

 one for the other ? 



Suppose two parts of one gas were mixed with twenty parts 

 of another gas, — how could the j)articles of the small quantity 

 of gas extend their pressure to each other onlr/, when such a 

 number of the particles of the predominating gas must be in 

 their way ? It appears to me more reasonable to suppose that 

 under those circumstances the different kinds of particles or their 

 atmospheres, which is the same in effect, nmst rest indiscrimi- 

 ziately on each other. 



Many objections have been made to this hypothesis, and many 

 more might be l^ronght forward were it considered necessary. 



I do not mako these cursory remarks with a view to completely 

 invalidate this hypothesis, for they are not sufficient to accom- 

 plish such an object. My reason for taking any notice of those 

 fonciful conceptions will ap])ear presently. I must say that it is 

 the only part of his New System uf Chemical Philosophy 

 that he has not borrowed; for the principal and most interesting 

 part was taken from my Compuru/ii/ff Ficw, as had been clearly 

 proved by many, and lately confirmed by mv own writinirs. 



But 



