HIEROGLYPHICS. 313 



EGYPTIAN HIEROGLYPHICS. HISTORY OF THE FIRST 



EXACT INTERPRETATION GIVEN OF THEM. 



The word hieroglyphic, regarded not metaphysically, 

 but in its natural acceptation, carries us into a field which 



that even in cases where that edge reflects any sensible amount of 

 light, its influence on the diffracted fringes is quite inappreciable. In 

 fact, Young, in a letter to Fresnel, in returning thanks for a copy of a 

 later memoir in which he had shown this supposition to be unneces- 

 sary, also concurs in abandoning it. It did but complicate and injure 

 the beauty of the result. 1 And every doubt must have disappeared in 

 the minds of those who compared the minute arithmetical accuracy 

 with which the places of the fringes, as computed from the simple 

 theory in the investigations of Fresnel, agreed with those actually de- 

 termined by the nicest micrometical measurements. 



In enumerating the discoveries of Young in the first establishment 

 of the wave theory, it is somewhat singular that Arago (whether from 

 accident or design) should have overlooked one investigation which 

 must be regarded as among the most important. The great support 

 which the emission theory received in recent times was that derived 

 from Laplace's memoir on the law of double refraction (1809), in 

 which, on the principle of "least action," as maintained by Mauper- 

 tuis and applied to the idea of luminous molecules, he explained the 

 observed laws of ordinary and extraordinary refraction in Iceland spar. 

 This investigation exercised a powerful influence in favor of the mole- 

 cular theory over the minds of the men of science in France who bowed 

 implicitly to the authority of Laplace. But the memoir of Laplace was 

 the siibject of a very powerful attack on the part of Dr. Young, carried 

 on in an article in the Quarterly Review, November, 1809, in which he 

 disputed the mechanical and mathematical grounds of Laplace's the- 

 ory, and showed that the same laws of double refraction could be far 

 more easily deduced from the undulatory hypothesis. Next to the 

 discovery of interference, this refutation of the strongest point of the 

 emission theory cannot but be regarded as one of the most material in 

 the development and establishment of the undulatory view. 



To the statement of these various cases of interference it should be 

 added that when the tints of polarized light were discovered, Young 

 in 1814, applied to the phenomena the general consideration ofinter- 



1 Young's Works, i. 393. 



SEC. SEK. 14 



