1242 



denominator, so that integrating, and choosing the integration constant 

 in such a way that in the infinite /«* lias the value c*, we find 



'"' = "'(•-" + 3 (12) 



So we have calcidated tiie gravitation field. Comparing (II) and 

 (12) we obtain 



71 10 = c . (13) 



and further we find (com p. I note on p. 1087) 



y^^c (14) 



Because of (10) s determines the electric ciiarge of the l)ody. The 



constant a determines tiie mass of the body. Formula (50) I gives 



namely 



4jr a 

 m— . (15) 



The same expression for m has been deduced in I p. 1087 for 

 the case c^l. Now we see that tliis expression also holds when 

 the unit of time has been chosen in another way. 



We obtained the relation (15) by aj)pIication of formula (50) 1, 

 where we assumed, that the matter has a finite extension. If the 

 electro-magnetic field is reckoned to the matter as is done in I, 

 the matter has, strictly speaking, an infinite extension. This has 

 however no influence on the validity of formula (50) I in the case 

 in question. The quantities of the electric field apju-oach namely 

 sufficiently to zero, when the distance from the centre increases. 



We may ask on what conditions (]^^ = w"^ can become zero 

 and negative. According to (12) m' becomes then infinite resp. 

 negative. The expression (12) shows that outside the body 



a I /«' 



tü» " for r = ~ rb / f *. 



2 1^ 4 



For smaller values of r w* is negative. 

 Only when 



a' 



iv^ becomes therefoi-e zero and negative for real values of r. If on 



the contrary f^ ^ — , then u)'' and u'^ are everywhere finite and 



positive. Then we may very well assume the mass and the charge 

 to be concentrated in a nialhematical point. 



