[ MCLENNAN-EDWARDS] ABSORPTION SPECTRA OF MERCURY 175 



able, therefore, to decide whether the sateUites have a real existence 

 or not. The Lummer plate pattern of this line showing just the one 

 simple component is reproduced in Fig. 13. For purposes of compari- 

 son the Lummer plate pattern of the mercury green line A = 5461 A°.U. 

 taken by one of us with the same Lummer plate interferometer is 

 shown in Fig. 14. The structure of this line has been discussed else- 

 where by McLennan and McLeod.^ In so far as this photograph goes 

 it shows the line to consist of a wide main component accompanied by 

 five satellites. 



V. The Ultra-violet Spark Spectrum of Cadmium. 



While the experiments which have been described above v^ere in 

 progress, a spectroscope provided with a fluorite train, made for us 

 by the Adam Hilger Co., was added to the equipment of the Physical 

 Laboratory at Toronto. With this instrument some preliminary 

 photographs were taken of the spark spectrum of cadmium in air in 

 the region below 2100 A°.U. As the plates showed a number of lines 

 in addition to those given by Eder and Valenta the experiments were 

 carefully repeated. Rods of the purest cadmium obtainable were used 

 as terminals for the spark gap. Photographs of the spark spectra of 

 zinc and aluminium were taken on the same plates and in measuring 

 up the wave-lengths of the lines in the cadmium spectra the following 

 well-known lines were used as standards. 



From the measurements it was easy to identify certain lines on 

 our spectra with those given by Eder and Valenta which appear to be 

 the only ones recorded for the spark spectrum of cadmium in the 

 region investigated by us. The wave-lengths of the lines found by us 

 were determined on the assumption that those given by Eder and 

 Valenta were correct. All the lines found by us together with their 



iMcLennan and McLeod. Proc. Roy. Soc, A. Vol. 90, p. 243, 1913. 

 ^Eder and Valenta. Atlas Typischer spectren, Wien. 

 ^Handke. Inaugural Dissertation, Berlin, 1909, p. 18. 



Sec. Ill, 1915—13 



