NEW PROPERTY OF REFLECTED LIGHT. ^Q 



contrary, when the principal section of the crystal was per- 

 pendicular to the plane of incidence, the extraordiaary ray 

 produced alone a partial reflection, and the ordinary ray 

 was refracted entire. 



The anj^ie usider which light experiences this modifica- Different bo* 

 tion in bein^j reflected at the surface of ditferent transpareiit the^Jff!^(.."!* 

 bodies is not the same in a!i« In general it is j^reat,est in diffeientan-' 

 those that refi;ict light most. Above and belo-w this angle ^ *''* 

 a part of the ray is more or less moditied, and in a manner 

 analogous to what takes place between two crystals, the 

 principal sections of which cease to be parallel or perpendi- 

 cular. 



If we would simply observe this phenotnenonj without Simple fexhi. 



measurine it accurately, we have only to place before 3^"'°""°^^^® 



^ • 1 • • I phenomenon, 



taper the transparent body, or the vessel contaming the 



liquid to be subjected to experiment. We must then 

 observe through a prism of flint glass the image of the flame 

 reSected at the surface of the solid or the liquid, pnd in 

 general two images will be seen : but on turning the crystal 

 round the visual ray as an axis, one of the images will be seen 

 to grow faint in proportion as the other increases in inten- 

 sity. Beyond a certain limit, the image that had grown, 

 weak begins to renew its intensity at the expense of the 

 second. At the point where the intensity of the light is 

 nearly a minimum, we must move the reflecting body nearer 

 to the taper, or farther from it, till the angle of incidence is 

 such, that one of the two images wholly disappears. This 

 distance being found, if we continue to turn the prisca. 

 slowly, we shall perceive, that one of the two images be** 

 , comes extinct alternately at every quarter of a revolution,,, 



The phenomfc-non 1 have mentioned in the rays that are Thephehome- 

 reflected under a certain angle at the surface of a transpa- "^" *^^* 

 rent body takes place likewise, but under a difl^erent angle, feflectT/ln^ 

 with the pencils reflected interiorly by the surface of emerg- '^^ interior of 

 ence; and the sine of the first angle vs to the sine of the* " « arn..*,. 

 second, as the sine of incidence to the sine of refraction* 

 Thus, if we suppose the face of incidence and the face of 

 emergence parallel to each other: and the ai^gle of incidence 

 such, that the ray reflected at the first surface presents the 

 phenomenon Ihave described; the ray reflect^jd at the 

 H 9 second 



