10 HISTORICAL INTRODUCTION. 



of the subject, which has been usually called the 

 atomic theory. I do not know when the ideas 

 first occurred to him. In all probability they 

 struck him by degrees, and were adopted in 

 consequence of his own experimental investiga- 

 tions. I first visited him at Manchester, on the 

 26th of August, 1804, and on that day, he ex- 

 plained to me his notions respecting the com- 

 position of bodies. The ultimate particles of all 

 simple bodies are, in his opinion, atoms incapable 

 of farther division. These atoms (at least 

 viewed along with their atmospheres of heat) 

 are all spheres, and are all of them possessed of 

 particular weights, which may be denoted by 

 numbers. And he represented the atoms of the 

 simple bodies by symbols. The following may 

 be taken as a specimen of his method : 



CHARACTERS. RELATIVE WEIGHTS. 



O Hydrogen ... 1 



Azote .... 5 



O Oxygen .... 6-5 



Carbon 5 



BINARY COMPOUNDS. 



O Water .... 7-5 



(DO Nitrous gas . . . 11-5 



Olefiantgas ... 6 



(DO Ammonia ... 6 



O Carbonic oxide . . . 11 '5 



TERNARY COMPOUNDS. 



Carbonic acid . . . 18 



