198 Mr. P. V. Sevan on the 



The Bed Channelled Space Ahsorption Spectrum. 



The interest of this spectrum and the other channelled' 

 spectra connected with the absorption by potassium vapour 

 lies in its similarity to the sodium absorption spectrum in the 

 neighbourhood of w.l. 5000. This region seems unconnected 

 with any bright lines in the various emission spectra and also 

 unconnected with any of the series lines of Kayser and Runge,, 

 or Rydberg. There is, howeAer, a certain amount of evidence 

 to connect this and the corresponding- spectrum of sodium 

 with the principal series of Kayser and Runge. Wood has 

 shown that there is an intimate physical relation between the 

 mechanisms which produce the D lines and this channelled 

 absorption, and it will appear that the potassium channelling* 

 are related to the first members of the principal series in a 

 manner similar to the corresponding sodium spectra. With 

 sufficient resolving power the channelled spectrum is seen to 

 be made up of a large number of fine lines ; the edges of 

 what appear as bunds are regions of greater absorption and lie 

 towards the violet end of the spectrum. This spectrum was 

 observed and the edges of the bands mapped by Roscoe and 

 Schuster *. Fresh measurements have been made for com- 

 parison with the corresponding sodium spectrum. Figure 2 

 shows the general appearance of the spectrum under as high 

 dispersion as the author was able to obtain. It is seen that 

 the spectrum consists of a number of fine lines which towards 

 the violet end of the spectrum are of equal intensity and 

 arranged at approximately equal intervals — the fluted appear- 

 ance is not observed here. Going from right to left we come 

 to the places where the changes in intensity give the fluted 

 appearance with definite edges, and as we come to the red 

 end we have a succession of bands equally diffuse on both 

 sides. On this spectrum the neon spectrum was photographed 

 for purposes of measurement. No definite relations amongst 

 the lines have been detected, but remembering the extreme 

 complexity of the similar sodium spectrum there seems no 

 chance of doing this until the fluorescent spectrum under 

 various conditions of excitation has been studied, as has been 

 done in the case of sodium by Wood. The definite edges of 

 the bands have been measured and it is of interest to compare 

 them with the corresponding edges in the case of sodium. 



The edges of the bands are at wave-lengths given in the 

 following table. The first column gives the number of the 

 band as designated in fig. 2. 



* Loc. tit. 



