Ill 



PHYSICS 



IN the later decades of the nineteenth century 

 there was a general feeling among natural 

 philosophers which, though not often explicitly 

 expressed, is evident in the writings of that time, 

 that the great guiding principles of this science 

 had been well and securely established, and that 

 little remained for workers in physics to do beyond 

 filling in the details of the subject. This state of 

 things has been entirely changed as a result of a 

 succession of remarkable discoveries, which started 

 with the discovery of the electron, the X-rays, 

 and radioactivity in the closing years of the nine- 

 teenth century. The consequence of these and of 

 succeeding discoveries has been a veritable revolu- 

 tion, with the result that the state of physics at 

 the present time is not unlike the contemporary 

 picture of the economic and political condition 

 of the globe. It is true that some of the old 

 principles as, for example, the fundamental laws 

 of thermodynamics have emerged from the 

 welter as securely established as ever. The laws 

 of dynamics as formulated by Newton and his 

 successors are now seen, on the other hand, to have 



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