THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 

 — * — 



X ^\^ [SIXTH SERIES] 



APRIL 1921. 



XLYII. On the Supposed Weight arid Ultimate Fate of 

 Radiation. By Sir Oliver Lodge *. 



IN regions where our ignorance is great, occasional guesses 

 are permissible. Some guesses occur in this paper : let 

 an apology for them be understood. 



If light is subject to gravity, if in any real sense light has 

 weight, it is natural to trace the consequences of such a fact. 

 One of these consequences would be that a sufficiently mas- 

 sive and concentrated body would be able to retain light and 

 prevent its escaping. And the body need not be a single 

 mass or sun, it might be a stellar system of exceedingly 

 porous character so that light could penetrate freely into 

 the interior and be subject to the combined gravitative 

 attraction of all the constituent masses. 



Given a material universe of any shape, bounded by a 

 surface S, with an aggregate mass M distributed anyhow 

 inside it, the average intensity of gravity, F, at the surface 

 is given by Green's theorem as — FS = 47rM. A large 

 enough mass, not spinning too rapidly, tends to be 

 spherical ; so, if the average density of the distributed 

 matter is p and the radius is R, \?= — f^/oR. 



If the distribution is taken as uniform, for the sake of an 

 example, that is with equably distributed masses and great 



* Communicated by the Author; being- the substance of an Address 

 to the Students' Math. & Phys. Soc. of the University of Birmingham. 

 Phil. Mag. S. 6. Vol. 41. No. 244. April 1921. 2 



