﻿'284: Mr. E. J. Evans on the 



The black body gives a continuous spectrum. What would 

 its brightness be when cut down to the narrow regions 

 occupied by the D-lines ? According to Abney's measures 

 the brightness of that part of sunlight which lies between 



the D's would be about ^g °f the whole. We may perhaps 



estimate the region actually covered by the soda lines as -^ 

 of this. At this rate we should get 



25 250 6250 ■ 



as the fraction of the whole radiation of the black body 

 which has the wave-lengths of the soda lines. The actual 

 brightness of a soda flame is thus of the same order of 

 magnitude as that calculated for a black body when its 

 spectrum is cut down to that of the flame, and we may infer 

 that the light of a powerful soda flame is due much more to 

 the widening of the spectrum lines than to an increased 

 brightness of their central parts. 



Terling Place, TVitham, 

 Dec. 18. 



XXXII. The Spectra of Helium and Hydrogen. 

 By E. J. Evans, B.Sc, AJt.C.Sc* " 



[Plate VI.] 



Intkoductiox. 



HP HE investigation of the series spectra of hydrogen and 

 JL helium has acquired considerable importance in con- 

 sequence of recent theories on the structure of the atom, and 

 the application of the quantum hypothesis to radiation 

 problems. 



It is known that some of the series spectra attributed to 

 hydrogen can be represented with great accuracy by the 

 Balmer-Rydberg-Kitz formula 



'-*(£-£) (1) 



where v represents the frequency, K Rydberg's universal 

 constant, and n Y and n 2 are whole numbers, if in equation 



(1) /'i = 2, and n 2 takes the successive values 3, 4, 5 , 



the ordinary hydrogen series in the visible spectrum is 



* Communicated by Sir E. Rutherford, F.R.S. 



