of Newton's Rings. 417 



These rings were examined with the combination of tonrmaline 

 and doubly refracting prism that I have described. When the 

 angle of incidence was small, the rings formed by light polarized 

 perpendicular to the plane of reflection were seen sufficiently 

 v,v,d, with black center, accompanied by the other set of rings 

 winch were faint. When the angle of incidence reached the 

 polarizing angle of the glass, the first set of rings disappeared. 

 On mcreasmg the angle, the first set of rings was again seen 

 with center white. In the most favourable state, the first set 

 ot nngs was much more faint than the second, but not so faint 

 that there could be the slightest doubt upon the fact of the 

 existence of the rings and the whiteness of the center, as I saw 

 them repeatedly with every change in the arrangement of the 

 apparatus, and saw a succession of several rings. The white 

 spot appeared larger than the dark spot in the other set of rings 

 but tins I nnagine is owing merely to the undefined nature "of 

 the spots, and to the circumstance that, in appreciating their 

 comparative extent, the eye always gives credit to the brightness 

 tor a greater surface than it can properly claim. T„ reS p ec t of 

 dimensions of corresponding parts, I could see no difference On 

 increasing the angle of incidence, the first set of rin^s a -a,n 

 disappeared, and reappeared in great brilliancy, the center bein<. 

 now black. 



I am willing to think these experiments important, because 

 they bear immediately upon a part • of Fresnel's theory which 

 has always appeared to me most liable to objection, namely the 

 formulae for the extent of vibration in reflected and refracted 

 rays. On the truth of Fresnel's general theory as a mere 

 geometrical representation, namely that light consists of transversal 

 v.brabons, and that polarized light is light in which all tin 



