HISTORICAL INTRODUCTION. 15 



ous proportions. Consequently very little ad- 

 vantage is gained by representing the atom of 

 hydrogen by unity ; but a very great one, by 

 representing the atom of oxygen by unity. 

 For it reduces the greater number of arithmeti- 

 cal operations, respecting these bodies, to the 

 addition of unity; and we see at once, by a 

 glance of the eye, the number of atoms of oxygen 

 which enter into combination with the various 

 bodies. Thus, if the atom of manganese be re- 

 presented by 3%5, and the weight of the various 

 oxides of that metal be as follows : 



1 Suboxide . . 4 



2 Protoxide . . 4-5 



3 Deutoxide . . 5 



4 Tritoxide . 5-5 



5 Manganesous acid . 6" 5 



6 Manganesic acid . 7'5 



It is obvious at once that the 



Suboxide contains | atom oxygen, 

 Protoxide 1 



Deutoxide 1 J 



Tritoxide 2 



Manganesous acid 3 

 Manganesic acid 4 



whereas, if we were to make the atom of hydro- 

 gen unity, these weights would be as follows : 



Manganese . . 28 

 Suboxide 32 



