100 HISTORY OF OPTICS. 



*vv/. 4. E.rplmiution of Polarisation ly the Undulatory Theory. 



EVEN while the only phenomena of polarization which were known 

 were those which affect the two images in Iceland spar, the difficulty 

 which these facts seemed at first to throw in the way of the undulatory 

 theory was felt and acknowledged by Young. Malus's discovery of polar- 

 ization by reflection increased the difficulty, and this Young did not 

 attempt to conceal. In his review of the papers containing this dis 

 covery* he says, " The discovery related in these papers appears to us 

 to be by far the most important and interesting which has been made in 

 France concerning the properties of light, at least since the time of 

 Huvghens ; and it is so much the more deserving of notice, as it crcatlv 



o o o / 



influences the general balance of evidence in the comparison of the 

 undulatory and projectile theories of the nature of light." He then 

 proceeds to point out the main features in this comparison, 'claiming 

 justly a great advantage for the theory of undulations on the two 

 points we have been considering, the phenomena of diffraction and of 

 double refraction. And he adds, with reference to the embarrassment 

 introduced by polarization, that w r e are not to expect the course of 

 scientific discovery to run smooth and uninterrupted ; but that we are 

 to lay our account Avith partial obscurity and seeming contradiction, 

 which we may hope that time and enlarged research will dissipate. 

 And thus he steadfastly held, with no blind prejudice, but with 

 unshaken confidence, his great philosophical trust, the fortunes of the 

 undulatory theory. It is here, after the difficulties of polarization had 

 come into view, and before their solution had been discovered, that we 

 may place the darkest time of the history of the theory ; and at this 

 period Young was alone in the field. 



It does not appear that the light dawned upon him for some years. 

 In the mean time, Young found that his theory would explain depo- 

 larized colors ; and he had the satisfaction to see Fresnel re-discover, 

 ainl M. Arago adopt, his views on diffraction. He became engaged 

 in friendly intercourse with the latter philosopher, who visited him in 

 England in 18] G. On January the 12th, 1817, in writing to this 

 gentleman, among other remarks on the subject of optics, he says, "J 

 have also been reflecting on the possibility of giving an imperfect ex- 

 planation of the affection of light which constitutes po'arization, with 



" Quart. Rev. May, 1810. 



