4 DOWNFALL OF CLASSICAL PHYSICS 



through the solar system, and our expectation is all the 

 other way. 



We shall return to the "solar system" atom in later 

 chapters. For the present the two things which concern 

 us are (i) its extreme emptiness, and (2) the fact that it 

 is made up of electrical charges. 



Rutherford's nuclear theory of the atom is not usually 

 counted as one of the scientific revolutions of the present 

 century. It was a far-reaching discovery, but a discovery 

 falling within the classical scheme of physics. The nature 

 and significance of the discovery could be stated in plain 

 terms, i.e. in terms of conceptions already current in 

 science. The epithet "revolutionary" is usually reserved 

 for two great modern developments — the Relativity 

 Theory and the Quantum Theory. These are not 

 merely new discoveries as to the content of the world; 

 they involve changes in our mode of thought about the 

 world. They cannot be stated immediately in plain 

 terms because we have first to grasp new conceptions 

 undreamt of in the classical scheme of physics. 



I am not sure that the phrase "classical physics" has 

 ever been closely defined. But the general idea is that 

 the scheme of natural law developed by Newton in the 

 Principia provided a pattern which all subsequent devel- 

 opments might be expected to follow. Within the four 

 corners of the scheme great changes of outlook were 

 possible; the wave-theory of light supplanted the cor- 

 puscular theory; heat was changed from substance (calo- 

 ric) to energy of motion; electricity from continuous 

 fluid to nuclei of strain in the aether. But this was all 

 allowed for in the elasticity of the original scheme. 

 Waves, kinetic energy, and strain already had their 

 place in the scheme; and the application of the same 

 conceptions to account for a wider range of phenomena 



