﻿Manchester Memoirs, Vol. xlix. (1904), No. IV 3 



absorbs the short wave-lengths. Using plates containing 

 gelatine as a substratum, leaving the sensitive silver salts 

 exposed to the direct action of the light,* Schumann 

 was able to announce in 1893 the discovery of lines in the 

 spectrum of hydrogen, having a wave-length which he 



o 



estimated at about 1,000 A. Owing to our imperfect 

 knowledge of the dispersion of fluorspar for these short 

 waves, it is impossible to determine accurately the wave- 

 length in a spectrum produced by means of a fluorspar 

 prism. 



No further attempts to measure these waves seemed 

 to have been made up to 1900. This is regrettable, because 

 it is probably in this region that a clue to the complicated 

 relationship of spectral lines will be found. For example, 

 the failure of Kayser and Runge to discover series in the 

 spectra of many elements may be due to the fact that 

 in these cases the series lie in the inaccessible ultra- 

 violet. It seemed, therefore, a grateful task to undertake 

 measurements in this region, and at the suggestion of 

 Professor Kayser I attempted this in 1 901 with a concave 

 grating. 



The apparatus was disposed in the manner indicated 

 in Fig. 1. 



D: 



Fig. 1. 



s * Wiei.i. Berichte, 1893. 



