C. GENERAL PHYSICS. 141 



IREADIATIOX. 



Le Roux states, as the results of his study of the optical 

 phenomena of irradiation, that these belong especially to the 

 field of indistinct vision, and that irradiation increases in 

 proportion to the distance of the image on the optic nerve 

 from the fovea centralis. For this latter portion of the retina 

 the phenomena do not exist ; for it there is no other irradia- 

 tion than that which results from the want of acuteness of 

 vision, and for the whole field of view irradiation is still a 

 question of acuteness of vision, and is explained physiologic- 

 ally by the progressive spacing of the sensitive elements of 

 the retina in proportion to their distance from Xhc fovea cen- 

 trails, the place of their maximum concentration. The pro- 

 duction of obscure ligaments between opaque contours is not 

 a phenomenon of irradiation, for then it would be a negative 

 irradiation, which means nothing; it is, he thinks, a phenom- 

 enon of imperfect accommodation, and is produced in contem- 

 plating objects with the naked eye as well as with telescopes ; 

 but one can make it disappear, or else exaggerate it, by caus- 

 ing the accommodation to vary. Among other interesting 

 phenomena, Le Roux has observed an obscure ligament, iso- 

 lated from each of its contours by luminous bands. 6 JS, 

 1873,960. ' 



POLARIZATIOX OF LIGHT BY EEFLECTION. 



When a ray of polarized light is reflected from a surface 

 of glass, the two principal components of the reflected ray ex- 

 perience no sensible difierence of phase, except Avhen the 

 anorle of incidence is in the nei2;hborhood of the anole of max- 

 imum polarization. At this point, within a comparatively 

 limited angular extent, there is established a rapidly increas- 

 ing difference of phase which soon becomes equal to a half- 

 wave length, when it remains constant, as the angle of inci- 

 dence increases up to the normal value of the polarizing 

 angle. If, now, the reflection takes place from a metallic sur- 

 face, the difference of phase, instead of changing so abruptly, 

 is produced in a uniformly continuous manner, in proportion 

 as the angle of incidence varies. The above propositions, 

 long since established, have now been connected together by 

 a very curious observation of M. Mascart. He has shown 



