138 Prof. 0. W. Pichardson : 



that of light, the potential at any point of the line in front 

 of the particle should tend to zero. 



Again, if a sphere be described round the moving charge 

 as centre, and the integral of normal force due to the moving 

 charge be taken over its surface, it will be found that, with 

 the simpler expression for the potential, the value of the 



€C G -4- U 



integral is ~- log - — , whereas with the expression given 

 above, it is e, in accordance with Gauss's Theorem, 



XII. Note on Gravitation. By 0. W. Richardson, F.P.S., 

 Wheatstone Professor of Physics, University of London, 

 King's College. With an Appendix, by L. Simons, D,Sc. t 

 Lecturer in Physics, University of Capetown *, 



THIS note is mainly a brief account of experiments 

 undertaken to seek a connexion between gravitation 

 and electricity. The line of attack is largely empirical and 

 follows a train of thought developed prior to the current 

 theories of gravitational relativity f. Although no positive 

 results have been obtained it seems desirable that a short 

 account of the experiments should be published, both on 

 account of the importance of the subject and also because 

 the results may set limitations on the possible scope of other 

 gravitational theories. The central idea was that oravita- 

 tion might be due to a slight modification of the law of force 

 between the positive and negative electrons out of which 

 matter is built up, such modification arising out of the 

 different amounts of energy associated with the respective 

 positive or negative electrons as evidenced by their different 

 masses. This point of view is to a certain extent anti- 

 pathetic to the relativity theory of gravitation, and its 

 comparative failure may be considered in some degree a 

 success for the latter. 



One consequence of the point of view referred to is that 

 the ratio between weight and mass should not be quite the 

 same for different elementary substances. The experiments 

 of Bessel and Eotvos show that this ratio is extraordinarily 

 constant for a number of substances. Nevertheless experi- 

 ments on this point were commenced by the writer in 1914, 

 were abandoned during the war, and have now been recom- 

 menced by Mr. H. H. Potter. The present note does not 



* Communicated by the Author. 



t O. W. Richardson, Phys. Rev. vol. xxxi. pp. 610, 709 (1910); 

 ' Electron Theory of Matter,' chap. xxii. (1914). 



