Contemporary Advances in Physics - XV The Classical Theory of Light, First Part

t h e existence, a n d n o one w i s h e s t o s u p p l a n t t h e m w i t h q u a n t a . Ripples on t h e s u r f a c e of a p o n d do f u r n i s h a precious e x a m p l e of w a v e motion, and I presume t h a t the notion of an undulatory theory was s u g g e s t e d o r i g i n a l l y b y t h e s e ; b u t i t i s precisely b e c a u s e t h e y a r e visible t h a t t h e y fail t o pose s o m e o f t h e q u e s t i o n s w h i c h i n d e a l i n g w i t h light a n d m a t t e r a r e t h e m o s t p e r p l e x i n g . W a t c h i n g t h e leaves a n d t h e s t r a w s w h i c h f l o a t u p o n t h e s u r f a c e o f t h e w a t e r , o n e sees t h a t t h e y d o not advance with t h e ripples; t h e y are heaved up a n d down as t h e crests a n d the troughs of t h e wavelets pass t h e m by. It is evident t h a t t h e w a v e s a r e n o t t o b e identified w i t h t h e w a t e r ; r a t h e r t h e y a r e a f o r m , a profile, a m o l d i n g of t h e s u r f a c e , w h i c h m o v e s r a p i d l y a l o n g while t h e s u b s t a n c e of t h e liquid oscillates o n l y a little. N o w in t h i s i n s t a n c e o f t h e ripples o n t h e p o n d , i t i s t h e r e l a t i v e l y - i m m o b i l e w a t e r w h i c h s e e m s s u b s t a n t i a l a n d real, while t h a t w h i c h i s p r o p a g a t e d a s a w a v e a p p e a r s to be m e r e l y a s h a p e or a c o n f i g u r a t i o n , n o t h i n g m o r e t h a n a geometrical abstraction.