RELATION OF VAPOUR AND AIR. 569 



which seemed to be exactly calculated to explain 

 the phenomena of vapour : 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. Berthol- 

 let had urged that we can hardly conceive the par- 

 ticles of a substance added to those 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 Mr. Gough, who argues, that if each gas is 

 elastic with regard to itself alone, we should hear, 

 produced by one stroke, four sounds ; namely, first, 

 the sound through aqueous vapour; 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 candour and impartiality. He there 

 appears disposed to abandon that part of the theory 

 which negatives the mutual repulsion of the parti- 

 cles of the two gases, and to attribute their dif- 

 fusion through one another to the different size of 



