44 THE ADVANCE OF SCIENCE 



ther proved that a certain number of the 

 chemically separable kinds of matter were 

 unalterable by any known means (ex- 

 cept in so far as they might be made to 

 change their state from solid to fluid, or 

 vice versa), unless they were brought into 

 contact with other kinds of matter, and 

 that the properties of these several kinds 

 of matter were always the same, whatever 

 their origin. All other bodies were found 

 to consist of two or more of these, which 

 thus took the place of the four ' elements ' 

 of the ancient philosophers. Further, it 

 was proved that, in forming chemical com- 

 pounds, bodies always unite in a definite 

 proportion by weight, or in simple multi- 

 ples of that proportion, and that; if any 

 one body were taken as a standard, every 

 other could have a number assigned to it 

 Keasser- as its proportional combining weight. It 

 Daiton was on this foundation of fact that Dal- 

 theorj\ 1C ton based his re-establishment of the old 

 atomic hypothesis on a new empirical 



