Frequencies in the Spectra of Various Elements. 165 



of 5*2 volts. o No. 3 shows the lines at \ = 3260'17A.U. and 

 \ = 2288'79 A.U. It was obtained with an impact voltage 

 equal to ro volts. 



III. Discussion of He suits. 



The results described above combined with those of 

 Bergen Davis and G-oucher go to support the view that 

 it is possible to stimulate the atoms of mercury, zinc, and 

 cadmium to the emission of definite and distinct types of 

 monochromatic radiation by choosing definite impact voltages 

 which are given by the quantum relation. A view has 

 been put forward that when the kinetic energy of the im- 

 pinging electrons is sufficient to bring ont the radiations 

 X = 2536-72 A.U, A = 3075*99 A.U., and \=326017 A.U., 

 for mercury, zinc, and cadmium respectively, other radiations 

 of still shorter wave Jength are present, but their intensity 

 is too weak to produce records of their presence on the 

 photographic plates. The experiments we have carried out, 

 however, do not support that view. Even with exposures 

 as long as 10 hours no trace of lines at \ — 2139*33 A. U. for 

 zinc and at A, = 2288'79 A.U. for cadmium came out when 

 the impact voltage was less than that given by the quantum 

 relation for their respective frequencies. When impact 

 voltages corresponding to their frequencies were applied, 

 these lines were at once obtained on the plates even with 

 comparatively short exposures. 



From Table I. it will be o noted that the wave-lengths 

 X = 2536-72A.IL, X=3075'99A.U. 5 and \ = 32()017A.U. 

 are respectively the first members of the combination series 

 j/=(l*5, S) — (m, p 2 ), and the wave-lengths \=1849'6 A.U., 

 \ = 2139-33 A.U., and \ = 2288'79 A.U., the first members of 

 the singlet principal series i/=(l'5, S) — (m, P). The other 

 members of both these series for the three metals are all 

 beyond the range of wave-lengths which can be recorded 

 by a spectroscope with an optical tram of quartz. It would 

 be interesting to extend the experiments described in this 

 paper so as to see if the higher members of these two series 

 came out on the plate one by one as the impact voltage of 

 the electrons was increased to that given by the quantum 

 relation for their frequencies. To do this it would ,be 

 necessary to use a fluorite spectrograph or a vacuum grating 

 spectrograph for the range intermediate between X= 1900A.U. 

 and \ — 1109 A.U. , and a o vacuum grating spectrograph for 

 the range below \= 1400 A.U. 



