DALTON 117 



infinitely small, and distant from each other." These 

 ideas were nothing more than a brilliant speculation. 

 The atomic theory remained a speculation for over two 

 thousand years, until Dalton discovered the law of 

 mutiple proportions, and deduced therefrom that matter 

 is composed of atoms having weights, and that the atoms 

 are of various kinds. When atoms of the same kind come 

 into juxtaposition, elements are formed, such as oxygen, 

 hydrogen, chlorine, etc. Compounds are formed from 

 the juxtaposition of different kinds of atoms, such as 

 water, ammonia, carbon dioxide, etc. 



This is not all : to Dalton's law of multiple propor- 

 tions, the law of Avogadro is adjoined. The latter law 

 establishes that all gases, temperature and pressure being 

 equal, have the same elastic force. As this force is pro- 

 bably due to the shock of atoms or groups of atoms 

 (molecules) on the sides of vessels which contain the gases, 

 it is evident that equal volumes of all elementary gases 

 contain the same number of molecules or atoms. And, 

 finally, Dulong and Petit proved that the atoms of the 

 elements all possess the same specific heat. All these 

 laws, which were the result of observation and experi- 

 ment in the early part of the nineteenth century, have 

 converted into a scientific theory the ideas of the 

 philosophers of ancient Greece. 



Dalton's laboratory was in the lower rooms of the 

 Manchester Literary and Philosophical Society, and 



