Manchester Mei)ioirs, Vol. Iv. (19 lo), No. 4. 15 



the experimental fact that the acid is formed by the 

 union of equal weights of the two elements. Higgins 

 proved, quite correctly on his supposition, that the atomic 

 weights of sulphur and oxygen are equal. But proof and 

 assumption are two very different things. Surely it is one 

 thing to prove a result in a particular case, and quite 

 another to assume the result in general. 



