698 Prof. McLennan and Mr. Edwards on the Absorption 



focussed with a cylindrical quartz lens upon the slit of the 

 spectrograph. 



The third spectrum in fig. 3 is the mercury vapour 

 absorption spectrum taken with the light from the Henri 

 spark. In the region below X = 2150 A.U. it will be seen 

 there is complete absorption. o The asymmetrical nature of 

 the absorption at X= 2536*72 A.U. is also brought out. At 

 \ = 2338 A.U. it will be seen that the absorption is complex, 

 and consists of four bands, one extending from X= 2313 A.U. 

 to A, = 2320 A.U., one at X=2322 A.U., another at X=2326 

 A.U.,and a wider one between X=2330 A.U. and X = 2338 

 A.U. The absorption moreover is strong and sharply edged 

 on the longer wave side, but it weakens out and is less clearly 

 defined on the side of the shorter waves. 



It will be noted that the third spectrum in fig. 3 also 

 shows a narrow absorption band at X=2288 A.U. As 

 cadmium vapour has an absorption band at this point, the 

 occurrence in the photograph of such a band was ascribed 

 to the presence of a trace of cadmium in the mercury. 



From these results it will be clear that between X = 6000 A.U. 

 and X = 1800 A.U. there are but three regions of absorption 

 in the absorption spectrum of non-luminous mercury vapour, 

 viz. in the neighbourhood of X=1849'6A.U., of X = 2338A.U., 

 and of X=2536-72A.U. It should be noted that X = 1849'6 

 A.U. is the first line in the series of the mercury-arc spectrum 

 given by v=l% S— to, P, and X = 2536*72 A.U. is the first 

 Hue iii the series o n = 2, p 2 — to, S* of the same spectrum. 

 The line X = 2338 A.U. has not been shown as yet to belong 

 to any series. 



III. Absorption Spectra of Cadmium and Zinc Vapours. 



It is interesting to note that in their paper on the absorp- 

 tion spectra of metallic vapours, Wood and Guthrie f found 

 absorption w o ith cadmium vapour at X = 2288 A.U. and at 

 X= 3260*17 A.U. As these lines are the first members in 

 the two series of lines in the cadmium arc spectrum given by 

 i/=l*5, S — to, P, and v — 2,p 2 — to, S,J there is a close analogy 

 between the absorption spectrum of non-luminous mercury 

 vapour and that of cadmium vapour. As zinc is chemically 



* Dunz, Inaugural Dissertation, Tubingen, 1911, pp. 67 & 68. 



t Wood and Guthrie, Ast. Phys. Journ. vol. xxix. No. 1, p. 211 (1909). 

 [The experiments of the writers confirm the findings of Wood and 

 Guthrie in regard to the absorption bands at A= 2288 A.U. and 

 X = 3260T7A.U. being the only ones observable in the absorption 

 spectrum of cadmium vapour.] 



J Dunz, loc. cit. 



