RELATION OF VAPOR AND AIR. 171 



the air's elasticity by vapor ; condensation by its various causes ; and 

 other phenomena. 



But Mr. Dalton also made experiments to prove Lis fundamental 

 principle, that if two different gases communicate, they will diffuse 

 themselves through each other ; 13 slowly, if the opening of commu- 

 nication be small. He observes also, that all the gases had equal 'sol- 

 vent powers for vapor, \vhich could hardly have happened, had che- 

 mical affinity been concerned. Nor does the density of the air make 

 any difference. 



Taking -all these circumstances into the account, Mr. Dalton aban- 

 doned the idea of solution. " In the autumn of 1801," he says, " I hit 

 upon an idea which seemed to be exactly calculated to explain the 

 phenomena of vapor : it gave rise to a great variety of experiments," 

 which ended in fixing it in his mind as a true idea. " But," he adds, 

 " the theory was almost universally misunderstood, and consequently 

 reprobated." 



Mr.- Dalton answers various objections. Berthollet had urged that 

 we can hardly conceive the particles of an elastic substance added to 

 Uiose of another, without increasing its elasticity. To this Mr. Dalton 

 replies by adducing the instance of magnets, which repel each other, 

 but do not repel other bodies. One of the most curious and ingenious 

 objections is that of M. Gough, who argues, that if each gas is elastic 

 with regard to itself alone, Ave should hear, produced by one stroke, four 

 sounds ; namely, first, the sound through aqueous vapor ; second, the 

 sound through azotic gas ; third, the sound through oxygen gas ; 

 fourth, the sound through carbonic acid. Mr. Dalton's answer is, that 

 the difference of time at which these sounds would come is very small ; 

 and that, in fact, we do hear, sounds double and treble. 



In his New System of Chemical Philosophy, Mr. Dalton considers 

 the objections of his opponents with singular candor and impartiality. 

 He there appears disposed to abandon that part of the theory which 

 negatives the mutual repulsion of the particles of the two gases, and 

 to attribute their diffusion through one another to the different size of 

 the particles, which would, he thinks, 14 produce the same effect. 



In selecting, as of permanent importance, the really valuable part of 

 this theory, we must endeavor to leave out all that is doubtful or un- 

 proved. I believe it will be found that in all theories hitherto promul- 



3 New Systc-.n of Chemical Philosophy, vol. i. p. 151. 

 14 3,'cic System, vol. i. p. 188. 



