REFLECTING POWER OF 



stal, and was made by sublimation ii. 



Mr. Tisdale of this laborator :i in 



:i this was done is described in 

 s _ The suit 



7 mm. and was one of tl 

 .zonal crystal. In these last exper; :ion was 



for the possibility of a variation of the intensi 

 light passing through the monoehromator. an-: 

 tion in the area of the crystal illuminated when it 

 through a right angle. The corrections were made as folic 



r.=the intensity of th orht ~hen th- 



- ong the crystal's long 



r 2 =the int^: - 'he reflected light when * 



is perpendicular to the crystal 



Oj==ihe reduction factor for the intensity due to th 

 through the monoehromator when the 



=the reduction factor when the vector is horizontal. 



=the fraction of the crystal illumine' 



is vertical. 



&,=the fraction illuminated when horizontal. 



Then r-A-Tj-. for example,, will be the inter- 



xperiment 'square of cosine of the ang tation 



for an intensity match' of the light reflecl 

 when both the vector and the " 



The other combinations are readily intei 



Let r.a.J)-=m 

 r.q_b=p 



r 2 a J ) r ==r l 



Solving these we obtain 



£ 1 



j. 2 = (mp nq) ; a a. = '7.\ \ - ; .= n m 



In the following table are listed the values of the squar 

 the cosine of the angle of rotation of the Nicol, V . for the dif- 

 ferent wave lengths, and for the four positions stated above. 

 It will be seen that the ratio of the tw ag powers is, 



ss in the ease of selenium, practically a constant throughout 

 the spectrum, the one with the electric vector along the long 



