362 Absorption Spectrum of Zinc Vapour. 



absorption bands correspond either to members of Paschen's* 

 single line series n=l*5, S — m, P, or to members of his 

 combination series ?* = 2, p 2 — m f S, in the emission spectra 

 of mercury, cadmium, and zinc. 



If zinc vapour acts in a manner analogous to that of 

 mercury and cadmium, the numbers given in the table 

 indicate that one should expect to find absorption with zinc 

 vapour at \3075*99. In the experiments of the writer with 

 this vapour every effort was made by strong heating to see if 

 absorption occurred in the neighbourhood of the line 

 A3075'99, but no evidence of any absorption was obtained. 

 It is just possible, however, that the failure to get absorption 

 in this region was due to the fact that in these experiments 

 either vapour of sufficiently high density or a spectrograph 

 of great enough resolving power was not used. 



Considering the character of the absorption band which 

 one obtains with mercury vapour at X2536*72, it may be of 

 interest to note that this band is, apart from its asymmetrical 

 nature which was first described by Wood *, in intensity 

 more like that which Wood and Guthrie f obtained with 

 cadmium vapour at \2288'79 and the writer with zinc vapour 

 at \2l39"33, than it is with the absorption which Wood and 

 Guthrie obtained with cadmium vapour at X326CK17. From 

 observations on such factors as intensity, line structure,. 

 Zeeman effect, and Doppler effect, Stark J has been led to 

 take the view that the line X253G*72 belongs to the mercury 

 single line series and that it is really the first member of that 

 series ; i. e., according to him the Hg line \2536'72 and not 

 the Ho- line \1849*6 is homologous with the CdlineX2288*79 

 and the Zn line \2139'33. The considerations regarding 

 absorption given above, it will be seen, lend some support to 

 his view. 



It would have been interesting to see if absorption also 

 occurred with mercury vapour at X1402*71, with cadmium 

 vapour at Xl669'3, and with zinc vapour at A.1589'64, as well 

 as at lines farther down in the single line series of these 

 metals, but to investigate this point it would have been 

 necessary to use an optical system of fluorite, and this 

 equipment the writer did not have at his disposal. 



Since the evidence adduced so far indicates that one should 

 expect to find absorption by these three vapours at the wave- 

 lengths mentioned above, it suggests that the lines of 

 Paschen's single line series in the emission spectra of 



* Wood, Phil. Mag. Aug. 1909. 

 t Wood aud Guthrie, he. cit. 



X Stark, Ann. der Phys. 1912, vol. xxxix. p. 1612; 1913, vol. xliu 

 pp. 238 & 243. 



