70 THE PROGRESS OF SCIENCE n 



extent to which our means of analysis take us, 

 material bodies consist of definite minute masses, 

 each of which, so far as physical and chemical 

 processes of division go, may be regarded as a unit 

 having a practically permanent individuality. 

 Just as a man is the unit of sociology, without 

 reference to the actual fact of his divisibility, so 

 such a minute mass is the unit of physico-chemical 

 science that smallest material particle which 

 under any given circumstances acts as a whole. 1 



The doctrine of specific heat originated in the 

 eighteenth century. It means that the same mass 

 of a body, under the same circumstances, always 

 requires the same quantity of heat to raise it to 

 a given temperature, but that equal masses of 

 different bodies require different quantities. Ulti- 

 mately, it was found that the quantities of In at 

 required to raise equal masses of the more peri'ect 

 gases, through equal ranges of temperature, were 

 inversely proportional to their combining weights. 

 Thus a definite relation was established between 

 the hypothetical units and heat. The phenomena 

 of electrolytic decomposition showed that there 

 was a like close relation between these units and 

 electricity. The quantity of electricity genera ted 

 by the combination of any two units is sufficient 

 to separate any other two which are susceptible of 



1 "Molecule " would be the more appropriate name for such ;i 

 particle. Unfortunately, chemists employ this term in 



sense, as a name for an aggregation of their smallest jiai tick's, 

 for which they retain the designation of '' atoms." 



