1881.] 



Some Experiments on Metallic Reflexion. 



487 



to the refractive index of the medium, not having been, as far as I 

 was aware, ever experimentally verified in the case of transparent 

 bodies in contact with media other than air, it appeared desirable to 

 make some experiments on this point, though there was every reason 

 for supposing that the law would be found to hold good. 



A crown glass prism was fastened to the vertical stage, the quarter 

 undulation plate and the analysing nicol removed, the polarising nicol 

 placed with its principal section in the plane of incidence, and the 

 angle of polarisation determined, a paraffine lamp being used as the 

 source of light. The thin glass vessel was then placed on the vertical 

 stage, and filled successively with water and carbon tetrachloride, and 

 the angles of polarisation again determined. 



Glass Prism. 



O / O i 



Angle of polarisation in air 57 14 57 02 



v y , „ water 49 41 49 43 



„ ,, carbon tetrachloride .. . 46 32 46 23 



The angles of polarisation in air are the mean of twelve and four 

 observations respectively, those in water of eight and twelve, and 

 those in carbon tetrachloride of twelve observations. 



When the surface of the glass was in contact with water or carbon 

 tetrachloride, its reflective power was so much diminished that it was 

 not possible to determine the angle at which the minimum amount of 

 light was reflected, and therefore the angles at which the light ceased 

 to be visible were observed, and the mean of these taken as the angle 

 of polarisation. 



The tangents of the angles of polarisation in water and carbon tetra- 

 chloride, when multiplied by the refractive indices of these liquids, 

 give the following values for the angle of polarisation in air : — 



O / 1 



Angle of polarisation in air observed 57 14 57 02 



Angle of polarisation in air calculated from ob- 

 servations in water 57 28 57 33 



Angle of polarisation in air calculated from ob- 

 servations in carbon tetrachloride 57 01 56 52 



The distilled water which was used in these experiments had not 

 been freed from air, and this may account for the values of the angles 

 of polarisation in air, calculated from the measurements made in 

 water, being somewhat too high. 



These observations show that, within the limits of experimental 

 error, Brewster's law holds good for glass in contact with water and 

 carbon tetrachloride, as well as air, and that in all probability it is 

 universally true for transparent bodies. 



2 m 2 



