THE REIGN OF LAW 163 



the atomic theory of the constitution of matter was 

 made definite and applicable to all the phenomena 

 known to chemistry. 



During the following months he returned to the 

 study of those cases in which the same elements 

 combine to form more than one compound. We 

 have seen that oxygen unites with nitric oxide to 

 form two compounds, and that into the one com- 

 pound twice as much nitric oxide (by weight) enters 

 as into the other. A like relation was found in the 

 weight of oxygen combining with carbon in the two 

 compounds carbon monoxide and carbonic acid. In 

 the summer of 1804 he investigated the composition 

 of two compounds of hydrogen and carbon, marsh 

 gas (methane) and olefiant gas (ethylene), and 

 found that the first contained just twice as much 

 hydrogen in relation to the carbon as the second 

 compound contained. In a series of compounds of 

 the same two elements one atom of one unites with 

 one, two, three, or more atoms of the other ; that is, 

 a simple ratio exists between the weights in which 

 the second element enters into combination with the 

 first. This law of multiple proportions afforded con- 

 firmation of Dalton's atomic theory, or chemical 

 theory of definite proportions. 



" Without such a theory," says Sir Henry Roscoe, 

 " modern chemistry would be a chaos ; with it, order 

 reigns supreme, and every apparently contradictory 

 discovery only marks out more distinctly the value 

 and importance of Dalton's work." In 1826 Sir 

 Humphry Davy recognized Dalton's services to sci- 

 ence in the following terms: "Finding that in cer- 

 tain compounds of gaseous bodies the same elements 



