﻿Rectification of the Spectrum. 947 



the grating had nominally 15,050 lines to the inch, and the 

 oblique rail R was 169'4 cm. long. Hence 



X = 



#2—^1 



15,050 x -3937 x 2 x 189-4 ~ 4 ' 98 X 10 " 7 (^ -*i> 



These values x 2 , #j, X, and N 2 o are given for the successive 

 values of 1ST 20 used, and fig. 3, which is therefore the corre- 

 sponding dispersion curve for carbon disulphide at 20°. 



5. Examples. Solid. — The treatment of a solid medium is 

 similar, except that the total reflexions are observed by 

 reflected light. If the data for carbon disulphide be taken 

 at 20°, 



» = ]Sr 2 o(l-a(£-~20))sin<£. 



Fig. 4 shows the values of the corrected sin <f> in terms 

 of x. The curves, as they should be, are nearly symmetrical 

 to the vertical, or (x 1 + x 2 )/2 is nearly constant for the same 

 sine. 



If now the distance apart of equal values of the reduced 

 sin (f> be taken, i. e., if # 2 —#i be found for suitable increments 

 of sin (j), the former values determine X, from which the 

 corresponding N 20 for carbon disulphide is found in turn. 



Fio-s. 4 & o. 



154 



m 



151 



y=6 l p 7p 8io y\o ffo m Wo idpcm 



41 43 45 47 49 5i 53 



57 59 61 63 65 



In this way the data for the values of n to be computed 

 are found, and n may now be expressed in terms of the X 

 used. If N 20 for carbon disulphide be taken from Kohlrausch's 

 tables, fig. 5 shows the final dispersion curves, index of 

 refraction n varying with wave-length X, for the glass of the 



3 Q 2 



