﻿Manchester Memoirs, Vol. xlix. (1904), No. IV 9 



moved by a micrometer screw between successive photo- 

 graphs, and after perhaps twenty or thirty attempts a 

 photograph would be secured with the shadow of the 

 point exactly on the centre of the line to be measured. 



The reading of the position of the grating was noted, 

 and the line again photographed in the same manner, 

 with the grating rotated into the second position. The 

 difference of the readings for the two positions of the 

 grating gave 281. 



Each line was determined relative to the aluminium 



o 



line of wave-length 1 862*8 A as A 2 . The wave-lengths of 

 the four sharpest lines were 



1785, 

 1741, 

 1709, 

 1693. 



From these lines the wave-lengths of all the lines 

 photographed by Schumann down to 1690 A can be 

 found by interpolation, and several metal spectra tested 

 for series. 



I wish to express my gratitude to Professor Kayser, of 

 Bonn, in whose laboratory the experiments were carried 

 out, for his valuable advice, for the invariable interest 

 which he took in the work, and for the loan of the costly 

 apparatus which he placed at my disposal. 



Most especially are my thanks due to Herr Hans 

 Hauswaldt for the use of his unique spectrograph and 

 fluorspar - grating, without which it would have been 

 impossible to carry out the research. 



