and the 1 Tieory of Atomic Structure. 1089 



understood to mean that there is an emission-band extending 



from ot 1 to a/. When one passes from Cd to Ag this band 



suddenly changes. For Ag two new lines could be detected : 



..... 

 one, which is within this emission-band, is called a 3 , the 



other, a short distance outside, is called « 4 *. The intensity 



of the line u z changes very little from Ag, where it is found 



for the first time, down to Rb. The line a 4 seems to become 



somewhat stronger for the lighter elements f . 



The satellites of fti take a different course. The proximity 

 of /3 4 makes it impossible to study these satellites for the 

 elements Ba and Cs, but from Sb (where they were observed 

 for the first time) down to Rb they do not essentially change. 

 Firstly there is an emission band, the short wave-length-edge 

 of which has been denoted by /3]'. This band is fainter than 

 the o^-band and not so sharply limited. Furthermore, out- 

 side the band a line has been found, denoted by /3 13 , which 

 is faint for the elements Sb-Rh, but becomes more intense 

 for the elements Mo-Rb. 



It is a well known fact that the human eye does not 

 always form a correct judgment of the blackening of a 

 photographic plate. In particular a sudden change in the 

 gradient of the blackening gives the impression of a white or 

 a black line. It therefore seemed to be advisable to study 

 the »!- and /^-satellites with the photometer also f. It must 

 be borne in mind, however, that even the photometer does 

 not give a wholly correct impression of the blackening of 

 the plate. With this photometer part of the photographic 

 plate is projected by a microscope-objective on the slit of 

 the thermopile. In these measurements 0*03 mm. on the 

 photographic plate corresponds to the breadth of the slit. 

 Further, it is impossible to have a sharp image for the 



* ^Note added during the proof.) — Recently, however, by taking some 

 other powerfully exposed plates, I was able to establish the existence of 

 the lines a 3 and a 4 for Cd also, but for this element they are very faint. 

 For In the existence of these lines remains very uncertain, for Sn no 

 trace of them could be observed. In this connexion it might be of 

 interest to remark that the appearance of these satellites is within wide 

 limits independent of the tension used on the tube. 



t I have previously observed the broadening of asi for the elements 

 Ta-U, but have interpreted it erroneously. See Zs.f. Phys. II. p. 191. 



X This photometer has been described bv M. Siegbahn, Ann.der Physik, 

 (4) xlii. p. 689 (1913), and A. E. Lindh, Zs. f. Phys. vi. p. 303 (1921), 

 See also W. J. H. Moll, Proceedings Phys. Soc. London, vol. xxxiii. 

 part 4, p. 207 (1921). 



Phil. Mag. S. 6, Vol. 43. No. 258. June 1922. 4 A 



