488 Prof, Q. Majorana : Theoretical and 



root of the energy-flux is proportional to the amplitude of the 

 electric vector in the light; and this leads to the view that the 

 rate of: ionization is in proportion to the maximum value of 

 the electric force operating on the atoms of selenium. This 

 seems probable enough. Too much stress should not, perhaps, 

 be laid at present on the quantitative aspect of this result. 

 The law C-O goI* or (C-C ) s <* it has been found to hold 

 for white light, in which, of course, the amplitude of the 

 electric vector has, at any moment, a variety of values corre- 

 sponding to the various frequencies; and there is no single 

 value which can be deduced from the total intensity simply 

 by taking the square root. Moreover, it is not just one 

 wave-length which affects selenium ; the effect is distributed 

 more or less throughout the spectrum. Further investigation 

 is required in this connexion ; and it has already been found 

 that the same law — viz., C — °c I ¥ , — holds when the light 

 red has been rendered more nearly monochromatic by using 

 a filter permitting the passage of 6300 to 7000 A.U. only. 

 Apart from the exact quantitative relation, however, the fact 

 remains that the rate of production of ions is not proportional 

 to the incident flux of energy. And this at least suggests that 

 the effect of light on selenium is in the nature of a " trigger " 

 action rather than the mere transformation of one kind of 

 energy into another. 



Imperial College. 

 Jan. 30, 1920. 



XLVIII. On Gravitation. Theoretical and Experimental 

 Researches. By Q. Majorana, Professor of Physics in the 

 Polytechnic School of Turin {Italy)*. 



f)RIGIN of the Researches.- — In a preceding paper f on the 

 theory of relativity and on the influence of the move- 

 ment of the source or of a mirror on the propagation of light, 

 I expressed the doubt whether among other unknown causes 

 that might have some influence on the phenomenon, there 

 might be the gravitational field of the earth. Without pre- 

 tending to connect now two orders of phenomena so different, 

 I shall give an account in this paper of some recent experi- 

 ments of mine on gravitation that have their origin in the 

 ones formerly described. 



* Commuuicated by the Author. Translated from the Italian by 

 A. Lion. 



t Phil. Mag. xxxv. p. 163 (1918) and xxxvii. p. 145 (1919). 



