160 MALUS. 



INVENTION OF THE REPEATING GONIOMETER. 



Physical theories and experimental methods have a 

 mutual reaction on each other. The former cannot be 



which " would probably long remain to mortify the vanity of an 

 ambitious philosophy, completely unresolved by any theory." 



Again, in a review of Malus's paper (in 1811), he considers it " con- 

 clusive with respect to the insufficiency of the undulatory theory in its 

 present state, for explaining all the phenomena of light." And again, 

 in a letter to Sir David Brewster, five years later, he expresses himself 

 thus: " With respect to my fundamental hypotheses respecting the 

 nature of light (i. e. the wave theory), I become less and less fond of 

 dwelling on them, as I learn more and more facts like those which 

 M. Malus discovers; because, though they may not be incompatible with 

 those facts, they certainly give no assistance in explaining them." * Even 

 Malus himself was at first of opinion that the phenomena of polariza- 

 tion were equally irreconcilable with both the undulatory and mole- 

 cular theories ; an opinion which he distinctly expressed in a letter 2 

 to Young. 



Somewhat later, however, we find Young beginning to entertain a 

 more satisfactory view of the case, as appears by the following pas- 

 sage from a letter addressed by him to Arago in 1817 : " I have been 

 reflecting upon the possibility of giving an imperfect explanation of the 

 affection of light which constitutes polarization, without departing 

 from the genuine doctrine of undulations. It is a principle of this 

 theory that all undulations are simply propagated through homoge- 

 neous mediums in concentric spherical surfaces, like the undulations 

 of sound, consisting simply of the direct and retrograde motions of 

 their particles in the direction of the radius, with their concomitant 

 condensations and rarefactions. And yet it is possible to explain in 

 this theory a transverse vibration, propagated also in the direction of 

 the radius, and with equal velocity; the motions of the particles bear- 

 ing a certain constant direction with respect to that radius ; and this 

 is polarization." 3 



Now that the idea of transverse vibrations has become familiarized, 

 it seems to present little difficulty; yet it was at first opposed to the 

 prepossessions even of the most zealous undulationists. Fresuel long 



1 Dean Peacock's Life of Young, p. 379. 



2 V\'orks, vol. i. p. 248, note. 



3 Life, p. 390. 



