CHAPTEE V. 



The Progress of Physics, 

 introductory. 



Definition of Physics. — ^^ The properties of matter 

 and energy, of energy and ether, and of ether and 

 matter, are the subjects of investigation in physical 

 science." Thus one of the modern masters, Prof. 

 G. F. Fitzgerald,* defined the scope of the science, 

 whose progress in the nineteenth century will be illus- 

 trated or suggested in this chapter. 



Although we may note Fitzgerald^s statement that 

 physical science is divided from chemistry ^^ by being 

 the study of each kind of matter by itself, while chem- 

 istry studies the actions of different kinds of matter 

 upon one another," we must also note his acknowledg- 

 ment — " of course no real ]ine can be drawn." 



The physicist has mainly to do with transforma- 

 tions of energy, or, in a word, with motion. Or per- 

 haps it is more accurate to say, with Professor J. J. 

 Poynting : " The range of the physicist's study con- 

 sists in the visible motions and other sensible changes 

 of matter. The experiences with which he deals are 

 the impressions on his senses, and his aim is to de- 

 scribe in the shortest possible way how his various 

 senses have been, will be, or would be affected." f 



Method of Physics. — The physicist looks out upon 

 nature seeking for similarities of action — likenesses 



* Science Progress, Vol. I., 1894, p. 3. 

 t Address, Section A, Rep. Brit. Ass. for 1899, p. 615. 



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