THE POLARIMETER 



67 



waves in motion in the same direction, the crests of one 

 corresponding to the hollows of the other, the vibrations of 

 the wave particles would obviously neutralise one another 

 and all motion would be stopped. Such a phenomenon is 

 termed the interference of waves. This interference may be 

 complete, as in the case just mentioned, which would occur 

 when one wave was exactly half a wave length behind the 



1 Wave-length 



1 Wave-length 



FIG. 10. WAVE MOTION. 



other; it would be less complete if the one wave were a 

 quarter or three-quarters of a wave length behind the other, 

 whereas a difference of a whole wave length would mean 

 that crest reinforced crest and hollow reinforced hollow, and 

 the amplitude of the vibrating particles would be doubled. 

 This is clearly seen from Fig. 10. 



It has been found that the physical properties of light 

 receive their full explanation if it is assumed that light 



F2 



