186 F. E. Wright — Transmission of Light through 



H, = circle on stage of microscope supporting universal stage. 



H, = outer horizontal circle of universal stage. 



II 3 = inner and smaller horizontal circle of universal stage. 



V, = large vertical circle of universal stage. 



V a = small vertical leaf circles on modified form of universal 

 stage. 



The source of light used in this instance was a Nernst light, 

 at the focus of a large condensing lens. The Abbe con- 

 densor lens system was removed from the microscope, so that 

 the entering light waves were as nearly parallel as possible. 

 For the exact location of the position of total extinction the 

 bi-quartz wedge plate was used. The upper nicol remained 

 fixed while the lower nicol was rotated to determine the 

 amount of rotation of the plane of polarization. 



The results of the observations are included in Table I, in 

 which the probable error of the average angles H is less than 

 10'. These measurements may be summarized by stating that 



TABLE I. 



i 



0} 



6' 



Calcu- 

 lated 



d'-u 



Headings 



22°30' 



22°30' 



22°50' 



22°53' 



0°20' 



22°50' 



50' 



51' 



48' 



51' 



51' 



52' 



51' 



52' 



52' 



( I 



45 00 



45 37 



45 33 



37 



45 38 



35 



37 



35 



36 



38 



38 



39 



39 



39 



tt 



67 30 



68 00 



67 53 



30 



68 00 



58 



01 



01 



00 



02 



00 



00 



01 



j01 



45 00 22 30 



24 19 



24 25 



1 49 



24 19 



16 



21 



17 



17 



20 



20 



20 



21 



21 



45 00 



47 35 



47 37 



2 35 



47 32 



33 



36 



32 



36 



37 



37 



36 



38 



34 



" , 67 30 



69 24 



69 18 



1 54 



69 19 



20 



25 



28 



25 



21 



28 



25 



25 



25 



for low angles of inclination of the glass plate, originally plane 

 polarized light is, after transmission, still practically plane 

 polarized, although its plane of polarization has been rotated 

 slightly, the amount of rotation increasing with the angle of 

 inclination. On each boundary surface a certain part of the 

 incident light is reflected and a certain part refracted. For an 

 isotropic body, as an object glass, there is a definite angle 

 (Brewster's angle) for which all reflected light is plane polar- 

 ized, while the refracted waves are partially polarized. In 

 fact, for every angle of incidence reflected natural light is par- 

 tially polarized in the plane of incidence. The refracted light 

 must, therefore, also be partially polarized normal to the plane 

 of incidence, as no light disappears. In this manner the 

 polarizing effect of a set of plates may be explained. If the 

 incident light be plane polarized, its plane of polarization is 

 rotated on refraction and the amount of rotation can be calcu- 

 lated from Fresnel's reflection and refraction formulas (46), 

 These formulas have been tested by numerous observers. 



