THE WAVP] THP:0RY OF LIGHT: ITS INFLUENCE ON 

 MODERN PHYSICS.^ 



By A. CoKNU.- 



Our era is distinguished froui preceding ages by wonderful utiliza- 

 tion of natural forces; man, that weak and defenseless being, has been 

 enabli^d by his genius to acquire an extraordinary power, and to l)end 

 to his use those subtle j^et dreadful agents wdiose very existence was 

 unknown to our ancestors. This marvelous increase of his material 

 power in modern times is due only to the patient and profound study 

 of natural phenomena, to the exact knowledge of the laws that gov 

 erned them, and to the skillful combining of their effects. But what 



^Printed in Nature July 27, 1899, with the following notes: "We are glad to be 

 able to publish this week a translation of the Rede lecture delivered at Cambridge by 

 Prof. Alfred Cornu, professor of experimental physics in the Eeole polytechnique, 

 Paris, and a foreign member of the Royal Society, on the occasion of the recent cele- 

 bration of the jubilee of Sir George Stokes as Lucasian professor of mathematical 

 physics. Professor Cornu delivered the lecture in French, and we are indebted to 

 him for the translation of his brilliant discourse." 



'■^ Besides the interest presented by a glance on the progress and the influence of 

 optical science, this lecture offers the conclusions of a careful study on Newton's 

 treatise of optics. It will be seen that the thought of the great physicist has been 

 singularly altered by a sort of legendary interpretation developed in the elementary 

 treatises where the emission-theory is exjiounded. In order to make the theory of 

 fits clearer, the commentators have imagined to materialize the luminous molecule 

 under the form of a rotating arrow offering now its head, now its side. This mode of 

 exposition has contributed to lead to the belief that the whole emission-theory was 

 comprehended in this rather childish image. 



Nowhere in his treatise does Newton give a mechanical illustration of the luminous 

 molecule: he confines himself to the description of facts, and sums them up in an 

 empirical statement without any hypothetical explanation. Moreover, he denies the 

 opinion that he raises any theory, though he holds occasionally as very probable the 

 intervention of the waves excited in the ether. 



So that the general impression resulting from tlie reading of the treatise, and 

 above all of the "queries" in the third Ixjok, is the following: Newton, far from 

 being the adversary of the Cartesian system, as he is commonly represented, looks, 

 on the contrary, very favorably at the principles of this system. Struck by the 

 resources which the undulatory hypothesis would offer for the explanation of the 

 luminous phenomena, he would have adopted it, if the grave objection concerning 

 the rectilinear i)rot)agation of light (only recently solved by Fresnel) had not pre- 

 vented him. 



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