PHYSICS 69 



apply the principles of mechanics, he was able to predict 

 phenomena hitherto unknown. Maxwell's work was not mere 

 mathematical manipulation. It is a well known fact that one 

 can never by mere mathematical processes discover physical 

 truths. One can never get more out of the equations than 

 one puts into them. The equations are simply abbreviated 

 methods of reasoning. Maxwell added several things ; he 

 laid great emphasis on the medium surrounding the electri- 

 fied body. He assumed that this medium, or ether as we 

 call it, possessed certain properties, and. further, that to this 

 medium and to the energ}' it contained could be applied the 

 simple and fundamental principles of mechanics. His success 

 in prediction was due to the laying down of certain hypotheses 

 and in doing that which I have said is characteristic of a 

 physicist, — that is, in extending the laws of energ}^ to this 

 case. 



There are a number of branches of science which are 

 often spoken of as the physical sciences. To explain fully 

 and clearly the distinctions between these subjects is im- 

 possible. Impossible for the sole reason that no line of 

 separation exists. Overlapping is found on every side. Be- 

 tween physics and chemistry it is very difficult to give even 

 a general statement. Our elementary texts formerly told 

 us that chemistry had to do with chemical changes and physics 

 with physical changes in matter. Chemical cTianges were 

 defined as those changes in substances in which the properties 

 of the substance was changed. For example, two clear liquids 

 mixed together produce a colored fluid, or from a trans- 

 parent crystal a heavy metal is extracted. Physical changes 

 were defined as those changes in bodies which produce no 

 changes in their properties ; for example, a change in position 

 or a change in velocity. Or stated in terms of the molecular 

 theory, chemistry was supposed to deal with the composition 

 of molecules, with the atom and all atomic phenomena. But 

 no chemist or physicist is limited by such a definition. To 



