166 THE HISTORY OF SCIENCE 



molecule of oxygen combines with one molecule of 

 hydrogen. The symbol for water is, therefore, not 

 HO but H 2 O. 



Enough has been said to establish Dalton's claim 

 to be styled a great lawgiver of chemical science. 

 His influence in further advancing definitely formu- 

 lated knowledge of physical phenomena can here be 

 indicated only in part. In 1800 he wrote a paper 

 On the Heat and Cold produced by the Mechanical 

 Condensation and Rarefaction of Air. This con- 

 tains, according to Dalton's biographer, the first 

 quantitative statement of the heat evolved by com- 

 pression and the heat evolved by dilatation. His con- 

 tribution to the theory of heat has been stated thus : 

 The volume of a gas under constant pressure ex- 

 pands when raised to the boiling temperature by the 

 same fraction of itself, whatever be the nature of 

 the gas. In 1798 Count Rumford had reported to 

 the Royal Society his Enquiry concerning the Source 

 of Heat excited by Friction, the data for which had 

 been gathered at Munich. Interested as he was in 

 the practical problem of providing heat for the homes 

 of the city poor, Rumford had been struck by the 

 amount of heat developed in the boring-out of can- 

 non at the arsenal. He concluded that anything 

 which could be created indefinitely by a process of 

 friction could not be a substance, such as sulphur or 

 hydrogen, but must be a mode of motion. In the same 

 year the youthful Davy was following independently 

 this line of investigation by rubbing two pieces of ice 

 together, by clock-work, in a vacuum. The friction 

 caused the ice to melt, although the experiment was 

 undertaken in a temperature of 29 Fahrenheit. 



