Hull — Initial Velocities of the Electrons. 259 



tial of about one volt on B is required to enable all the elec- 

 trons produced on A to escape is probably due to two causes. 



(1) Reflection of the electrons from B. O. v. Baeyer* has 

 shown that even a lampblack surface reflects diffusely about 

 ten per cent of the electrons which strike it. The better satu- 

 ration obtained by Ladenburg and Markau may be explained 

 by the fact that their apparatus had a blackened wire gauze in 

 front of the lampblacked surface corresponding to B, which 

 still further lessened the reflection. 



(2) Entanglement of the diffusely radiated electrons by the 

 rough surface of the blackened radiator A. If a blackened 

 surface so entangles the electrons which strike it as to prevent, 

 in a large measure, their reflection, it is probable that it also 

 hinders, to some extent, their escape from the illuminated plate. 



The question whether the electrons liberated by light of a 

 particular wave-length are all of one velocity or of several 

 velocities is of great importance to the theory of the photo- 

 electric effect, and the author proposes to extend the work of 

 Ladenburg and Markau on this subject to the region of shorter 

 wave-lengths. 



Before concluding, the author wishes to express his thanks 

 to Professor Bumstead, at whose suggestion this investigation 

 was undertaken, for his interest in the work, and to Professor 

 Boltwood for many valuable suggestions. 



Summary. 



The initial kinetic energy of the electrons liberated from 

 carbon by light between X 1710 and X 1230 has been measured, 

 and the proportionality, discovered by Ladenburg, between 

 the maximum initial velocity of the electrons, i. e. the square 

 root of their maximum initial kinetic energy, and the fre- 

 quency of the light producing them, has been found to hold 

 for these short wave-lengths, to the degree of accuracy with 

 which this part of the spectrum is known. It may now be 

 stated that, for the entire range, X 2700 to X 1230, the initial 

 velocities of the fastest electrons liberated by light of particu- 

 lar frequencies are proportional to these frequencies. The 

 question of the production of electrons other than the fastest 

 will be further investigated. 



* O. v. Baeyer, Phys. Zeitschr., x, p. 181, 1909. 



