CHAPTER VI 



THE REALITIES OF SCIENCE 



IN the classification of the phenomena which are 

 physical rather than chemical, it was natural to cor- 

 relate them according to the senses by which they are 

 perceived. The subjects into which physics has 

 usually been divided are mechanics, heat, sound, 

 light, and electricity and magnetism. Thus under 

 "light" and " sound" were classed those natural 

 phenomena which affected the optic and the auditory 

 nerves. "Heat" included those affecting what has 

 been called the "temperature sense." "Mechanics" 

 included phenomena of motion and of forces. Elec- 

 tricity and magnetism, which are now grouped to- 

 gether, were for a long time considered separate 

 divisions. They dealt with the motions and forces 

 of which electricity and magnetism are the causes. 



A classification according to senses is unsatisfactory. 

 Light does not exist for one who is blind, nor sound for 

 one who is totally deaf. Either exists only in so far 

 as we ourselves are concerned and have certain nerves. 

 For the color-blind, as for example those who fail to 

 perceive the greens, light of this color does not exist, 

 although it may for others. Those of normal vision 

 may have a sensation which they call green light, but 

 this means not that green light is real but only that an 

 impression is real to them. Light is not an objective 

 but a subjective reality. 



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