﻿Path of an Electron in Neighbourhood of an Atom. Ill 



the cathode (S.). The range of p + and p_ is about 

 10 dyne/cm. 2 . 



4. It is yet not certain whether the law connecting P 

 with I is a linear one, and whether the pressure does arise 

 with every current strength (D.), or requires a current 

 minimum (S.). Probably with increasing I, the pressure 

 P does not increase by a uniform law, for the graphs show 

 some " Knees", which suggest different arc stages (S.). 



5. The value P calculated, in testing the recoil hypothesis, 

 by taking for the velocity of the carbon particles their atomic 

 speed, is too great (D.). Whilst, by taking the propulsion 

 velocity of carbon atoms starting from the positive crater, 

 the calculated repulsion is in a far better agreement with the 

 experimental results (S.). 



6. The propulsive velocity of carbon particles has been 

 estimated as 280-400 cm./sec. (S.). 



In conclusion, I think we cannot yet say with full knowledge 

 whether the observed effect is intimately associated with the 

 electrical processes of the arc, or whether it simply accom- 

 panies in an ordinary way the evaporation of electrodes at 

 high temperature. Only after having established the former 

 view by further investigations, available information on the 

 nature of the arc will be given by P measurements, im- 

 proving the theoretical construction whose foundations have 

 been established by Thomson, and Stark. 



Istituto fisico della R. Universita, 

 Palermo, 22 March, 1922. 



LXVII. J lie Path of an Electron in the Neighbourhood of an 

 Atom. By Bevan B. Bakek, M.A., B.Sc, F.R.S.E., 



Lecturer in Mathematics in the University of Edinburgh *. 



1. T7XPERIMENT has shown that when an electron 

 Pi collides with an atom, thereby causing it to emit 

 radiation, the frequency v of the radiation is related to the 

 amount U of the kinetic energy of the electron absorbed by 

 the atom by the equation 



V = hv, 



where h denotes Planck's constant of Action. Professor 

 Whittaker f has recently shown that, in order that all 



* Communicated by the Author. 



t E. T. Whittaker, " On the Quantum Mechanism in the Atom/' Proc. 

 Roy. Soc. Edin. xlii. pp. 130-142 (1922). 



