REPORT ON PHYSICAL OPTICS. 351 



From this " wonderful phenomenon," as Huygens justly- 

 called it, it appeared that each of the rays refracted by the first 

 rhomb had acquired properties which distinguished it altogether 

 from solar light. It had, in fact, acquired sides ; and it was 

 evident that the phenomena of refraction depended, in some un- 

 known manner, on the relation of these sides to certain planes 

 within the crystal. Such was the conclusion of Newton : " This 

 argues, " says he, " a virtue or disposition in those sides of the 

 rays, which answers to, and sympathizes Avith, that virtue or 

 disposition of the crystal, as the poles of two magnets answer 

 to one another." 



This conception was followed out by Mai us, whose varied 

 and important discoveries respecting the nature and laws of 

 polarized light have justly placed him in the rank of fovmder in 

 this most interesting branch of science. The molecules of a 

 polarized ray wei-e supposed by him to have all their homolo- 

 gous sides turned in the same directions. He adopted the term 

 " polarization" to express the phenomenon, and compared the 

 effect to that of a magnet which turns the poles of a series of 

 needles all to the same side. M. Biot has modified the hypo- 

 thesis of Malus in order to embrace the other phenomena of 

 light, and assumed that there was one line, or axis, similarly 

 placed in each molecule, and that these axes in a polarized ray 

 were all turned in the same direction. The molecules, however, 

 are at liberty to revolve round these axes, and thus to assume 

 different dispositions with respect to the attracting or repelling 

 forces to which they are exposed when they encounter the sur- 

 face of a new medium. 



The phenomenon of polarization seems to have had much 

 weight with Newton in forcing him to reject the theory proposed 

 by Huygens: " It is difficult," he says, "to conceive how the 

 rays of light, unless they be bodies, can have a permanent vir- 

 tue in two of their sides, which is not in their other sides, and 

 this without any regard to their position to the space or medium 

 through which they pass *." " Are not all hypotheses errone- 

 ous," he adds in another place, "in which light is supposed to 

 consist in pression or motion, propagated through a fluid me- 

 dium ? . . . . Pressions or motions, propagated from a shining 

 body through an uniform medium, must be on all sides alike ; 

 whereas by those experiments it appears that the rays of light 

 have different properties in their different sides f-" In this ob- 

 jection Newton seems to have fixed his thoughts upon that 

 species of undulatory propagation whose laws he himself had 



* Optics, book iii. Query 29. f Query 28. 



