Spectra of Mercury, Cadmium, and Zinc Vapours. 695 



IV. Three new lines were discovered in the infra-red 

 spectrum at T067 p, 1-090 /m, and 1*270 fi. 



V. It has been pointed out that the frequency differences 

 for the lines 1038/x, 1*270 fi, and 3*02 p are the same as 

 those which characterize the triplets in the subordinate 

 series for the mercury arc spectrum given by v~2, p — m, d 

 and v = 2, p — m, s. It has also been suggested that possibly 

 the lines at 1*09 p and 1'367 yu, are the third and second 

 members of a similar triplet with its first member in the 

 neighbourhood of 3*70 ft. 



The Physical Laboratory, 



University of Toronto. 

 May 1st, 1915. 



LXXII. On the Absorption Spectra of Mercury, Cadmium, 

 and Zinc Vapours. By Professor J. 0. McLennan, F.R.S., 

 and Evan Edwards, M.A., B.Sc, University of Toronto *, 



[Plate XVI.] 



I. Introduction. 



IN 1907 it was pointed out by Wood f that in the absorption 

 spectrum of non-luminous mercury vapour there is a 

 heavy band at \=2536'72 A.U., and a less sharply-defined 

 one at \ = 2350 A.U. In a later paper by Wood and Guthrie J 

 dealing with the same subject no mention is made of the 

 absorption band at A, = 2350 A.U., but it is stated that with 

 dense mercury vapour there is a fairly strong band at 

 X = 2338 A.U., and another very broad one at \ = 2 140 A.U. 

 From the work of Kirschbaum § and others it is known that 

 light of wave-length \= 1849*6 A.U. is strongly absorbed by 

 mercury vapour. 



The absorption band at X = 2536'72 A.U. has been shown 

 by Wood to be asymmetrical. It is sharply defined on the 

 shorter wave-length side, but with increasing vapour density 

 it gradually spreads out towards the red end of the spectrum. 

 With low vapour densities it consists of two bands, the one 

 at X = 2536 A.U. and the other at \ = 2539A.U. The band 

 at \= 2338 A.U. , which is probably the same one as that 

 originally given by Wood at X = 2350A.U., does not appear 



* Communicated bv the Authors, 

 t Wood, Astr. Phys. Journ. vol. xxvi. p. 41 (1907). 

 t Wood and Guthrie, Astr. Phys. Journ. vol. xxxix. No. 1, p. 211 

 (1909). 



§ Kirschbaum, Electrician, vol. lxxii. p. 1074 (1914). 



