Frequencies in the Spectra of Various Elements. 471 



in the zinc flame spectrum \ = 2139*66 A.U. might come 

 out too. No trace of it, however, was found. With calcium 

 no trace of the line \ = 2721A.U. of frequency v=(l'5, S) 

 — (3, P) was found in the flame spectrum. It is also of 

 interest to note that with calcium no trace of the line 

 X = 6598 A.U. of frequency v = (1*5, $)— (2, p 2 ) was 

 obtained. Since the line \ = 4226'91 A.U. of frequency 

 v=(l*5, S) — (2, P) came out so feebly, it was scarcely to 

 be expected that the line \ = 2721A.U., z/=(l'5, S)— (3, P), 

 or others of higher frequency in the series^ = (l*5, S) — (w,P) 

 would have been obtained. It should be remembered, how- 

 ever, that even in the spark or the arc spectrum of calcium 

 the line A, = 2721 A.U. possesses relatively small intensity. 



The results obtained with flame spectra in the present 

 investigation as well as those obtained by McLennan and 

 Thomson, it will be seen, do not afford much information as to 

 the relative importance of the two series v = (l'5, S) — (in, p 2 ) 

 and i/ = (l'5, S) — (in, P) from the point of view of funda- 

 mentally. 



Summary of Results. 



1. It has been shown that when zinc and cadmium vapours 

 respectively are bombarded by electrons whose kinetic energy 

 is gradually increased, monochromatic radiation is suddenly 

 emitted by the vapour when the impact voltage is that given by 

 the quantum relation for the frequency v = (l'5, S) — (2, p 2 ). 

 When the impact voltage was increased beyond this amount 

 no additional radiation was observed until that corresponding 

 to the frequency ^ = (1*5, S) — (2, P) was applied. When these 

 conditions were realized the wave-lengths whose frequencies 

 are given by z/=(l'5,8) — (2,p 2 ) a "d i/ = (l\5,S) — (2, P) were 

 then recorded on the plates. 



2. It lias been shown that when a Bunsen flame is fed with 

 the vapour of heated zinc, it is possible to obtain monochro- 

 matic radiation of wave-length A = 3075*99 A.U. 



3. The evidence adduced goes to show that the series of 

 wave-lengths given by z/ = (1*5, S) — (w, P) is probably 

 fundamental from the point of view of electronic vibrations 

 within the atoms of the elements mercury, zinc, cadmium, 

 magnesium, calcium, and probably also strontium, and barium. 



The Physical Laboratory, 

 University of Toronto. 



