TRANSACTIOXS OF SECTION A. 605 



Whether they can or cannot exist, however, the general results of the investigation 

 are not affected. 



Since this paper was published Larmor has read a second one on the same 

 subject before the Royal Society, developing further his theory of the electron. 

 The publication of this will be awaited with interest. It is impossible in an 

 address such as this to go seriatim into the numerous points which he takes up and 

 illuminates, because the mathematical treatment of the general question does not 

 lend itself easily to oral exposition even to an audience composed of professed 

 mathematicians. There is no doubt but that this paper has put the theory of a 

 rotationally elastic ether — and with it that of a fluid vortex ether — on a sounder 

 basis, and will lead to its discussion and elucidation by a wider circle of investi- 

 gators. 



One further class of physical phenomena yet remains, viz., those of gravitation. 

 The ether must be capable of transmitting gravitational forces as well as electric 

 find optical efiects. Does the rotational ether give any promise of doing this ? No 

 satisfactory explanation of gravitation on any theory has yet been ofiered. Perhaps 

 the least unsatisfactorj- is that depending on the vortex atom theory of matter, 

 which attributes it to pulsations of hollow vortex atoms. But this necessitates 

 that they should all pulsate with the same period and in the same phase. It is 

 very difficult to conceive how this can happen, unless, as Larmor suggests, all 

 matter is built up of constant elements like his electrons, whose periods are neces- 

 sarily all alike. It is possible tliat the vortex cell theory of the ether, of which I 

 have alreadj^ spoken, may suffice to explain gravitation also. The cells, besides 

 their rotational rigidity, have, in addition, as we saw, a peculiar elasticity of form. 

 To get an idea of how this theory may account for weight, let us suppose the 

 simplest case where all the cells are exactly alike, and the medium is in equilibrium. 

 Now suppose one of the cells begins to grow. It forces the medium away on all 

 sides : the cells will be distorted in some definite way, and a strain set up. Further, 

 this strain will be transmitted from the centre, so that the total amount across any 

 concentric sphere will be the same. Stresses will therefore be set up in the whole 

 medium. If a second cell begins to grow at another place it will produce also a 

 state of strain, the total strain depending on the presence of both. The stresses 

 called into play in the medium will produce a stress between the bodies, but it 

 is questicmable whether it would be inversely as the square of the distance. 

 Whether it would be an attraction or repulsion can only be determined b}- mathe- 

 matical investigation. The problem is quite determinate, though probably a very 

 difficult one, and would be of mathematical interest quite apart from its physical 

 importance. Since apparently the phenomena of gravitation have no direct "inter- 

 action with those of light and electricity, whilst the mind rejects the possibility of 

 two different media occupying the same space, we seem driven to look for it in an 

 independent structure of the same medium. Such a structure is already to our 

 hands, with its effects waiting to be determined. It may well be that it may 

 prove to be the cause we are seeking. 



The rapid survey I have attempted to make is no doubt a medley of suppositions 

 and inferences combined with some sound deductions. This is the'necessary conse- 

 quence of a prospecting survey in a region whose surface has been merely scratched 

 by pioneers. My object has been to show that this theory of an ether, based on a 

 primitive perfect fluid, is one which shows very promising signs of being able to 

 explain the various physical phenomena of our material universe. Probably, nay 

 •certainly, the explanations suggested are not all the true ones. Some will have to 

 be given up, others modified with further knowledge. We cannot proceed to 

 particularise in our secondary hypotheses until we know more about the properties 

 of such media as we have been considering. Every special problem solved in 

 vortex motion puts us in a position to form clearer ideas of what can and what 

 cannot happen. The whole question of vortex aggregates and their interactions is 



' 'On the Problem of Two Pulsating Spheres in a Fluid,' Proc. Camh. Pldl 

 Soc, iii. p. 283. 



