July 12, 1932] 



SCIENCE 



67 



by botanists tbe world over. So it will be with 

 the Slime Moulds, that are "passing," to he 

 replaced by the Slime Animals. 



Charles E. Bessey 

 The University op Nebraska 



SCIENTIFIC JOUENALS AND ARTICLES 

 The May number (Vol. 18, No. 8) of the 

 Bulletin of the American Mathematical So- 

 ciety contains the following papers : " Definite 

 integrals containing a parameter," by D. C. 

 Gillespie ; " On the Y' with five binodes of 

 the second species in 8 J' by S. Lefschetz; 

 " What is mathematics " (review of White- 

 head and Eussell's "Principia Mathematica "), 

 by J. B. Shaw; Eeview of Bianchi-Lukat's 

 " Differentialgeometrie," by L. P. Eisenhart; 

 " Notes " ; " New Publications." 



The June number of the Bulletin contains : 

 Report of the April meeting of the Chicago 

 Section, by H. E. Slaught; Eeport of the 

 twenty-first regular meeting of the San Fran- 

 cisco Section, by T'. M. Putnam; "Implicit 

 functions defined by equations with vanishing 

 Jacobian," by G. E. Clements; Eeview of 

 Darwin's Scientific Papers, by E. W. Brown; 

 Eeview of Pareto's " Manuel d'Economie po- 

 litique," by E. B. Wilson ; " Notes " ; " New 

 Publications." 



SPECIAL ARTICLES 



THE LAWS OF PHOTOELECTRIC ACTION AND THE 



UNITARY THEORY OF LIGHT (LICHT- 



QUANTEN THEORIE) 



In a note which was published in a recent 

 number of Science (Vol. 35, p. 783, May 17, 

 1912) Dr. Karl T. Compton and the writer 

 announced, as the result of experiments, cer- 

 tain conclusions they had come to regarding 

 the relation between the number and kinetic 

 energy of the electrons emitted by different 

 metals under the influence of light, on the one 

 hand, and the frequency of the light and the 

 position of the metals in the voltaic series, on 

 the other. The following brief outline of a 

 method of deducing and extending these laws 

 from theoretical considerations, is not without 

 interest. 



Let N^ be the number of electrons emitted 

 in unit time by unit area of a metal in the 

 presence of unit density of isotropic radiation 

 of frequency between v and v -\- dv, let r,„ 

 represent the maximum kinetic energy of 

 these electrons and T^ their mean kinetic 

 energy. The writer"" has shown that N„ and 

 T„i have to satisfy equations which can be 

 reduced to 



s: 



N,h 



-hvjBedv = AiO^e-^olse 



(1) 



and 



P N„T„hv^e->"'IRB dv = 2AiIWh-^olJi0. (2) 



In these equations h is Planck's radiation 

 constant, A^ is a constant characteristic of the 

 material and independent of the temperature 

 ^, w„ is the internal latent heat of evaporation 

 of one electron at the absolute zero and R is 

 the gas constant reckoned for a single mole- 

 cule. The following is a solution of equa- 

 tions (1) and (2) : 



JV. = 0, for < Ad < «■„, (3) 



T„^hv — tOo, for W(, <i hv <C_ oo . (5) 



Equations (1) and (2) have to be slightly 

 modified when reflection of the electrons is 

 taken into account. The result does not ap- 

 pear to make any important difference in (3) 

 and (4) but, instead of (5), we get 



T^ = s{hv — Wo), for Wo<ihv <l X), (6) 

 where s is the ratio between the proportion of 

 the incident energy which is absorbed, and the 

 proportion of the incident matter (or elec- 

 tricity) which is absorbed, from the stream of 

 electrons which returns to the body in a state 

 of thermal equilibrium. It can be shown that 

 s lies between zero and unity. 



If we define v^ by the equation w„ = hv^ it 

 can easily be shown that the experimental re- 

 sults announced by Dr. Compton and the 

 writer are confirmatory of equations (3), (5) 

 and (6). One of the most interesting conse- 

 quences of the theory is equation (4) which 

 has not yet been tested by experiment. 



^Fhys. Rev., Vol. 34, February and May, 1912; 

 FUl. Mag., Vol. 23, p. 615, 1912. 



