( 166 ) 



CHAPTER X. 



TRANSVERSAL VIBRATIONS THEORY OF REFLEXION AND RE- 

 FRACTION OF POLARIZED LIGHf. 



(179) HAVING in the preceding chapter stated the prin- 

 cipal facts of polarization, we may proceed to consider their 

 connexion with the physical theory. 



It is strange that the department of optics, in which the 

 wave-theory now stands unrivalled, should be the very one 

 which Newton selected as affording the most decisive evidence 

 against it : "Are not," says he, " all hypotheses erroneous, 

 in which light is supposed to consist in pressure, or motion, 

 propagated through a fluid medium ? .... for pressures 

 or motions, propagated from a shining body through an uni- 

 form medium, must be on all sides alike ; whereas it appears 

 that the rays of light have different properties in their diffe- 

 rent sides/' In this objection Newton seems to have had his 

 thoughts fixed upon that species of undulatory propagation 

 whose laws he himself had so sagaciously unfolded. When 

 sound is propagated through air, the vibrations of the particles 

 of the air are performed in the same direction in which the 

 wave advances ; and if the vibrations of the ether which con- 

 stitute light had been of the same kind, the objection would 

 be insuperable. For, if the particles of the ether vibrated 

 in the direction of the ray itself, the ray could not bear a 

 different relation to the different parts of the. surrounding 

 space. 



But the case is altered, if the vibrations of the ethereal 

 particles be performed in a transverse direction. Let us sup- 



