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III. 



PHOTOGKAPHS OF SPAEK-SPECTEA FEOM THE LAEGE 

 EOWLAND SPECTEOMETEE IN THE EOYAL UNIVEE- 

 SITY OF IRELAND. PAET II. 1 : THE ULTEA-VIOLET 

 SPAEK-SPECTEUM OF EUTHENIUM. ByW. E. ADENEY, 

 D. Sc., A. E. C. Sc. I., Curator and Examiner in Chemistry in 

 the Eoyal University of Ireland. 



[Read January 20 ; Eeceived for Publication January 23 ; Published 

 August 7, 1903.] 



Reproductions of photographs of the spark-spectra of the plati- 

 num and other metals from the 21 '5 ft. Rowland spectrometer 

 in the Royal University, Dublin, have already been published 

 in the Scientific Transactions of this Society, vol. 7, 1901. 



Scales of approximate wave-lengths were ruled on the nega- 

 tives from which the reproductions were prepared ; and it was at 

 first hoped that, with their aid, it would be possible to easily 

 identify the spectral lines with those previously given in various 

 tables of wave-lengths for the same metals, and that consequently 

 it would not be necessary to exactly measure the lines. 



More recent work, however — more especially that on the effect 

 of pressure upon the wave-length of lines in the electric arc, 2 and 

 on displacement of the spark-lines analogous to those in the arc 3 — 

 has rendered it advisable to accurately measure all the lines on 

 the photographs. 



The measurements of the spectrum which forms the subject 

 of this communication, have been made by means of a light 

 microscope mounted on a stage which can be moved through a 

 space of about one inch long by a short micrometer screw. Each 

 line has been measured at least twice, and many of them three 

 and four times. 



Kayser's values 4 for the well-defined lines in the arc-spectrum 



1 Tor Part I. see Trans. E.D.S., Vol. vn., 1901, p. 331. 



2 Humphreys and Mohler, Astrophysical Journal, 1896, 1897. 



3 E. Haschek, Spectroscopic Studies, Astrophysical Journal, 1901. 



4 Kayser, Konigl. Preuss. Akadenrie der Wissenchaften zu Berlin, 1897. 



