PHYSICS 67 



moon was really falling towards the earth and that the same 

 law governed it that applied to any falling body. 



We can sum all this up by saying in the words of Hertz 

 that "all physicists agree that the problem of physics consists 

 in tracing the phenomena of nature back to the simple laws 

 of mechanics." This now gives us a definition of physics. It 

 is a definition of method rather than of scope. And it is 

 to understand this attitude and method of the physicist that 

 I have gone so much in detail into the fundamental concepts. 



To repeat, the physicist assumes that the fundamental 

 laws of nature are simple; that the simple laws which were 

 found to be true in relatively simple cases, that is, in the 

 motions of ordinary bodies, are far more general. He finds 

 that these laws of mechanics apply to such things as heat, 

 light, electricity, cases which are not motions of ordinary 

 bodies. Wherever then he finds energy or force, he assumes 

 at once that to this may be applied the simple fundamental 

 laws. The physicist we may then say is that man who is 

 continually trying to explain all the facts of nature by means 

 of his simple laws of motion, force, and energy. 



While all physicists may agree that this interpretation 

 of his purpose is correct, still they differ in the methods they 

 employ. The work of some is experimental; others are 

 what we call theoretical or mathematical physicists. The 

 experimental physicist devotes his time primarily to finding 

 new facts or to verifying certain hypotheses. The only road 

 to truth is through experiment. But these truths must be 

 classified, generalizations must be made, and here the field 

 is open to the theoretical physicist. Science is built from 

 facts, not a haphazard collection, but facts carefully cata- 

 logued. As a matter of fact, all physicists employ both of 

 these methods, but they differ in the amount of time they 

 give to each. So when we say that a man is an experimental 

 or a theoretical physicist, we are speaking in a relative manner. 



