1908] on the Ether of Space. 63 



based. First of all, Newton recognised the need of a medium for 

 explaining gravitation. In his " Optical Queries " he shows that if 

 the pressure of this medium is less in the neighbourhood of dense 

 bodies than at great distances from them, dense bodies will be driven 

 towards each other ; and that if the diminution of pressure is 

 inversely as the distance from the dense bodv, the law will be that 

 of gravitation. 



All that is required, therefore, to explain gravity is a diminu- 

 tion of pressure, or increase of tension, caused by the formation of a 

 matter unit — that is to say of an electron or corpuscle : and although 

 we do not yet know what an electron is — whether it be a strain 

 centre, or w^hat kind of singularity in the ether it may be— there is 

 no difficulty in supposing that a slight, almost infinitesimal, strain or 

 attempted rarefaction should be produced in the ether whenever an 

 electron came into being — to be relaxed again only on its resolution 

 and destruction. Strictly speaking it is not a real strain, but only a 

 " stress " ; since there can be no actual yield, but only a pull or tension, 

 extending in all directions towards infinity. 



The tension required per unit of matter is almost ludicrously 

 small, and yet in the aggregate, near such a body as a planet, it 

 becomes enormous. 



The force with which the moon is held in its orbit would be 

 great enough to tear asunder a steel rod four hundred miles thick, 

 with a tenacity of 30 tons per square inch ; so that if the moon and 

 earth were connected by steel instead of by gravity, a forest of pillars 

 would be necessary to whirl the system once a month round their 

 common centre of gravity. Such a force necessarily implies enormous 

 tension or pressure in the medium. Maxw^ell calculates that the 

 gravitational stress near the earth, which we must suppose to exist in 

 the invisible medium, is 3000 times greater than what the strongest 

 steel could stand ; and near the sun it should be 2500 times as great 

 as that. 



The question has arisen in my mind, whether, if the whole sensible 

 universe —estimated by Lord Kelvin as equivalent to about a thousand 

 million suns — were all concentrated in one body of specifiable density,* 

 the stress would not be so great as to produce a tendency towards 

 etherial disruption ; which would result in a disintegrating explosion, 

 and a scattering of the particles once more as an enormous nebula and 

 other fragments into the depths of space. For the tension would be 

 a maximum in the interior of such amass ; and, if it rose to the value 

 10^^ dynes per square centimetre, something would have to happen. 

 I do not suppose that this can be the reason, but one would think 

 there must be some reason, for the scattered condition of gravitative 

 matter. 



* On doing the arithmetic, however, I find the necessary concentration 

 absurdly great, showing that such a mass is quite insufficient.^ See Appendix, 



