302 THOMAS YOUNG. 



The theory of Thomas Young is not amenable to this 

 criticism. Here there is no longer admitted any peculiar 

 kind of "fits" as primordial properties of the rays. 

 The thin film is here assimilated in all respects to any 

 thicker reflector of the same substance. If at certain 

 points in its surface no light is visible, Young did not 

 conclude that therefore its reflexion had ceased ; he sup- 

 posed that, in the special directions of those points, the 

 rays reflected by the second surface proceeded to meet 

 with those reflected from the first surface, and com- 

 pletely destroyed them. This conflict of the rays is 

 what the author designated by the term " interference" 

 which has since become so famous. 



Observe then here the most singular of hypotheses ! 

 We must certainly feel surprised at finding night in full 

 sunshine, at points where the rays of that luminary 

 arrive freely ; but who would have imagined that we 

 should thence come to suppose that darkness could be 

 engendered by adding light to light ! 



A physicist is truly eminent when he is able to an- 

 nounce any result which, to such an extent, clashes with 

 all received ideas ; but he ought, without delay, to gup- 

 port his views by demonstrative proofs, under the pen- 

 alty of being assimilated to those Oriental writers whose 

 fantastic reveries charmed the thousand and one nights 

 of the Sultan Schahriar. 



It was nothing more than the strict inference that at those points suc- 

 cessively something occurred in the course of the ray which disposed it 

 for, or induced, reflexion in the one case, and non-reflexion in the 

 other; accompanied in the latter case by the like tendency to trans- 

 mission. These apparent "fits" must be still acknowledged as phe- 

 nomena ; the mechanism by which they are produced is, however, now 

 known to be nothing inherent in the light, no essential property re- 

 curring, but the simple periodicity of conspiring or counteracting 

 wave-action. Translator. 



