456 Proceedings of the Royal Society of Edinburgh. [Sess. 
the means of revealing series among the spectrum lines, or of showing 
relationships between the element under examination and others which 
have been similarly investigated. 
The photographic part of the experiments made on this subject were 
carried out in the University of Gottingen, and the author is indebted to 
Professor Voigt for the use of the Rowland grating and its equipment. A 
research grant from the Carnegie Trust met the cost of the photographic 
materials and of the Zeiss comparator. 
(. Issued separately July 28 , 1910 .) 
