﻿MancJiester Memoirs, Vol. xlix. (1904), No. It. 7 



The wave-lengths were determined in the following 

 manner : — 



When the grating is situated symmetrically with 

 respect to the collimating and camera tubes, we have 



2^sine = 27i- (see Fig. 3), 



2 



where d is the distance between consecutive lines on the 

 grating, 2e the angle between the axes of the collimator 

 and camera tube, and A is the wave-length of the 

 particular light which happens to fall in the centre of the 

 camera ; n is a constant equal to unity if the spectrum is 

 of the first order. 



AXIS OF CAMERftTUBE 



PLANE OF QRATINQ 



AXIS OF COLLI MM-OR 



have 



or 



If the grating is rotated through an angle &, we shall 



(i{sin(^ -f e) - sin(^ - e) } = n\ (see Fig. 4), 

 2^cos^sin E^nX^ 



