THE CENTURY'S PROGRESS IN PHYSICS 



through a grove of trees." He asserted his belief also 

 that the chemical rays which Hitter had discovered 

 beyond the violet end of the visible spectrum are but 

 still more rapid undulations of the same character as 

 those which produce light. In his earlier lecture he 

 had affirmed a like affinity between the light rays and 

 the rays of radiant heat which Herschel detected below 

 the red end of the spectrum, suggesting that " light 

 differs from heat only in the frequency of its undu- 

 lations or vibrations those undulations which are 

 within certain limits with respect to frequency affect- 

 ing the optic nerve and constituting light, and those 

 which are slower and probably stronger constituting 

 heat only." From the very outset he had recognized 

 the affinity between sound and light.; indeed, it had 

 been this affinity that led him on to an appreciation 

 of the undulatory theory of light. 



But w r hile all these affinities seemed so clear to the 

 great co-ordinating brain of Young, they made no such 

 impression on the minds of his contemporaries. The 

 immateriality of light had been substantially demon- 

 strated, but practically no one save its author accepted 

 ; the demonstration. Newton's doctrine of the emission 

 of corpuscles was too firmly rooted to be readily dis- 

 lodged, and Dr. Young had too many other interests to 

 continue the assault unceasingly. He occasionally wrote 

 something touching on his theory, mostly papers con- 

 tributed to the Quarterly Review and similar period- 

 icals, anonymously or under a pseudonym, for he had 

 conceived the notion that too great conspicuousness in 

 fields outside of medicine would injure his practice as a 

 physician. His views regarding light (including the 

 original papers from the Philosophical Transactions of 



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