POLARIZATION TRANSVERSAL VIBRATIONS. 79 



glaringly does this blemish show itself in that part of the theory 

 which has been last under consideration, that one of its advocates 

 says, " Bevera illae vices reflexionis et transitus, cum omnibus 

 additamentis fictitiis, mirabiliores adhuc sunt quam phenomenon 

 ipsuin, ad cujus explicationem in usum sunt vocatse."* The same 

 attribute appears in the broader divisions of the science. The 

 several classes of phenomena do not flow from the theory as from 

 one common source ; but each has its separate and independent 

 head, and its separate and independent data. In the wave-theory, 

 on the other hand, not only the individual laws, but the classes of 

 phenomena are related ; and to calculate, numerically, the laws of 

 refraction, the varied phenomena of diffraction, and those of thin 

 plates, we only need to borrow one result from experience, the 

 length of a wave of light in each medium. There is thus estab- 

 lished that connexion and harmony in its parts which is the never- 

 failing attribute of truth. But powerful as is the weight of this 

 intrinsic evidence in favour of the wave-theory, it has yet stronger 

 claims to our assent. These claims are grounded on the vast body 

 of new phenomena which it explains, and explains (it is to be 

 remembered) not in a vague and general manner, but in the pre- 

 cise language of analysis, and with an accuracy which the refine- 

 ments of modern observation have not been able to impugn. It 

 may be confidently said that it possesses characters which no false 

 theory ever possessed before. 



PART II. POLARIZED LIGHT. 

 I. Polarization. Transversal Vibrations. 



In the various phenomena which have been hitherto described 

 as taking place when a ray of light encounters the surface of a new 

 medium, it has been assumed that the direction, and the intensity 

 of the several portions into which it is subdivided, are wholly inde- 

 pendent of the manner in which the ray is presented to the bound- 

 ing surface, the direction of the ray remaining unchanged. In 

 other words, it was taken for granted that a ray of light had no 

 relation to space, with the exception of that dependent on its direc- 



* Mayer on Newton's Rings. GWingen Memoirs, vol. v. p. 22. 



