Light and the Quantum 



Johnson, to Boswell: "Sir, to leave things out of a book, 

 merely because people tell you they will not be believed, is 

 meanness." 



ONE of the oldest dilemmas of philosophy 

 is that between continuity and discontinu- 

 ity, involving also the much discussed question 

 of action at a distance. I believe it was Carlyle 

 who, granting that matter acts only where it is, 

 asked, "But where the devil is it?" Where mat- 

 ter is and where it acts, and whether it is to be 

 regarded as a continuum or a discontinuum, 

 are questions concerning which the scientific 

 mind has changed in recent years, and probably 

 will change still further in the near future. 



Although the idea that matter might be com- 

 posed of indivisible particles had long been cur- 

 rent in philosophy and in common speech, phys- 

 ics and chemistry up to the time of Dalton had 

 been developed in terms of the continuum. In- 

 deed, it is within our own lifetime that the atom 

 and the molecule, from being mere working 

 hypotheses, have come into a high degree of 

 reality. Yet even now if it is asked whether the 



