Adeney — Photographs of Spark Spectra from the Rowland Spectrometer. 333 



spectrum could be focussed on each plate, and hence any general resemblance 

 between the spectra of similar elements was not rendered obvious.* 



The ultra-violet spectra obtained with the quartz spectrograph, while showing 

 the differences in the lines, gave a dispersion in the ultra-violet region which was 

 sufficient for all practical purposes. So important were the characteristics of the 

 lines considered to be that a large amount of labour was expended in giving a 

 minute description to each one of them, as well as their positions and wave-length 

 measurements. 



The only other observers who had given particular descriptions of the lines 

 previously, and those only in the visible spectrum, were Thaldn and Lecocq de 

 Boisbaudran. 



Photographs of spectra render any detailed descriptions of the lines now 

 unnecessary, but attention may be directed to the. fact that methods of producing 

 spark spectra latterly employed fail to render the characteristic features of several 

 well-marked groups of elements. 



Other investigators have since published photographs of spark spectra, namely, 

 Crew and Tatnall,t and F. McClean, m.a.J (these range from D to H only), and 

 Eder and Valenta.§ In the first-mentioned memoir a table of corrections is 

 given for converting Hartley and Adeney's measurements from Angstrom's to 

 Rowland's scale. Eder and Valenta's beautiful reproductions of spectra show 

 that many of the features previously preserved are wanting in theirs. The same 

 remark ma}^ be applied also to Exner and Haschek's jjhotographs of the spark 

 spectra of the elements. In both series the mode of producing the sparks 

 differed from that which had been previously commonly resorted to, and 

 concave gratings were employed. 



It would be a remarkable fact if the measurements published in 1884 did 

 not require revision for purposes of physical i-esearch, since at that period the 

 properties of Rowland's concave gratings, which had so largely increased the 

 accuracy of spectroscopic work, had not been discovered. 



Fifteen of the spectra were entirely new to science, and the wave-lengths 

 assigned to the lines have for all practical purposes been proved sufficiently accurate 

 and of great utility in chemical investigations of a diverse character. 



In view of the attention now being given, not only to the numerical relation- 



*Phil. Trans., vol. clxxxv., p. 63, 1884. 

 t Phil. Mag. (5), vol. xxxviii., p. 379, 1894. 



{"Comparative Photographic Spectra of the Sun and the Metals." Monthly Notices of the Roy. 

 Astron. Soc, vol. lii., No. 1. 



§ " Beiti-age zur Spectralanalyse," K. Akademie der Wissenschaften (Wien), 1892 to 1899. 



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