244 PHYSICAL SCIENCE 



we find two such differing types of radiation as 

 heat and light on the one hand and X-rays on 

 the other, we may well guess that the many 

 planetary electrons revolve in different rings, 

 X-rays coming from the Inner, and heat and 

 light from the outer rings. This guess has 

 been abundantly supported by evidence In more 

 recent research. 



Hitherto, wonderful as are the results 

 described, they Involve no breach with the old 

 and well-tried principles of Newtonian dynamics. 

 The paths of a particles, deflected by atoms of 

 a gas, show the law of inverse squares, and the 

 atomic corpuscles whirl round in their orbits as 

 the planets round the sun. But, if we push our 

 analysis further, we find that we are forced to 

 assumptions which are not in accord with this 

 familiar scheme of science. We are brought to 

 contemplate conditions which we cannot explain 

 on any known principles, conditions which, in the 

 present state of knowledge, seem not only In- 

 explicable but inconceivable to our minds. It 

 may be that future years will see these difficulties 

 resolved by human insight as so many others 

 have been. But we must not overlook the possi- 

 bility that the orderliness we perceive in nature 

 may be merely the rediscovery of conventions we 

 have ourselves inserted when framing the problems 

 to be Investigated. We choose mass and energy 

 as convenient fundamental physical quantities. 

 But, all unconsciously, this choice is made 

 because mass and energy happen to remain 

 constant throughout a series of physical and 

 chemical changes — and then triumphantly we 



