THE STORY OF NINETEENTH-CENTURY SCIENCE 



them perfectly, while, as Young affirmed with confi- 

 dence, no other theory hitherto advanced could explain 

 them at all. Taking all the evidence together, Young 

 declared that he considered the argument he had set 

 forth in favor of the undulatory theory of light to be 

 " sufficient and decisive." 



This doctrine of interference of undulations was the 

 absolutely novel part of Young's theory. The all- 

 compassing genius of Kobert Hooke had, indeed, very 

 nearly apprehended it more than a century before, as 

 Young himself points out, but no one else had so much 

 as vaguely conceived it ; and even with the sagacious 

 Hooke it was only a happy guess, never distinctly out- 

 lined in his own mind, and utterly ignored by all others. 

 Young did not know of Hooke's guess until he himself 

 had fully formulated the theory, but he hastened then 

 to give his predecessor all the credit that could possibly 

 be adjudged his due by the most disinterested observer. 

 To Hooke's contemporary, Huyghens, who was the orig- 

 inator of the general doctrine of undulation as the ex- 

 planation of light, Young renders full justice also. For 

 himself he claims only the merit of having demonstrated 

 the theory which these and a few others of his prede- 

 cessors had advocated without full proof. 



The following year Dr. Young detailed before the 

 Royal Society other experiments, which threw addi- 

 tional light on the doctrine of interference; and in 1803 

 he cited still others, which, he affirmed, brought the 

 doctrine to complete demonstration. In applying this 

 demonstration to the general theory of light, he made 

 the striking suggestion that " the luminiferous ether 

 pervades the substance of all material bodies with little 

 or no resistance, as freely, perhaps, as the wind passes 



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