LECTURE IV. 



RICHTER'S INVESTIGATIONS DALTON'S ATOMIC THEORY GAY-LUSSAC'S 

 LAW OF VOLUMES AVOGADRO'S HYPOTHESIS WOLLASTON'S 

 EQUIVALENTS. 



I SHALL now proceed to describe the development of the 

 atomic theory, up to the second decade of this century, in so 

 far as it possesses scientific interest. It is beyond my inten- 

 tion, in doing so, to enter into the hypotheses of the Greek: 

 and Roman philosophers regarding the constitution of matter. 

 That Leucippus and Democritus regarded matter as composed 

 of ultimate particles, and that Lucretius afterwards expounded 

 these views at length, merely shows to us, what we have long 

 known, that there were men amongst the Greeks and Romans 

 who might in every respect be placed beside our thinkers of 

 to-day. These philosophers made use of the deductive method 

 of reasoning ; they started from general principles, although 

 their conclusions from them were not always in accord with 

 observations. The latter were of relatively small importance, 

 especially as at that time experimentation, or the art of in- 

 vestigation under stated conditions, was practically unknown. 

 For this reason, Democritus cannot be placed in front of Kant, 

 who, starting from the opposite view from the dynamic 

 hypothesis constructed the universe in perhaps just as logical 

 a fashion. The expenditure of talent and sagacity which we 

 observe on the part of the supporters of the two views, was in 

 vain ; the observations by means of which such questions could 

 be solved, were entirely wanting. 



The scientific development of the atomic theory depended 

 simply upon the discovery of a series of facts which were con- 

 nected together by it, and found in it a simple explanation. 

 It is my business now to mention these experiments, and to 



