Gravitation and Light

Abstract

IN a recent letter (NATURE, December 25, p. 412) and elsewhere I have expressed doubt as to the security of the inferences regarding the influence of gravitation on the light from distant celestial bodies, which are advanced as tests of the Einstein formulation. A closer and less sceptical general scrutiny is possible. The difficulty was to recognise how a theory which professes to supersede an æther with its definite space and time, by concepts purely relativist, could manage to effect direct comparison, at a distance and without tracing transmission across the intervening space, of the radiations of a molecule at the sun and those of a molecule of the same substance at the earth. This body of doctrine seems, in fact, to consist of two chapters. A blind man could work out the purely relativist theory, which would indeed represent rather closely the process of groping from point to adjacent point in space and time by which he must acquire his own scheme of knowledge. But to compare his results with the world of experience a practical astronomer is needed, with very different equipment; he relies on the rays of light, in conformity with the optical theory that prescribes their function as messengers across space.