THE ELECTRIC AND LUMIRIEEROUS MEDIUM. 
805 
Coiitiudion. 
112. The foimdcitiou of the present view is the coiice})tiou of h iiiediuiu whii-h has 
the properties of a perfect incompressible fluid as regards irrotatioual motion, but- is 
at the same time endowed with an elasticity which allows it to be the seat of energy 
of strain and to propagate undulations of transverse type ; and the question discussed 
is how far such a simple type of medium affords the means of co-ordination of physical 
phenomena. This idea of a medium with fluid properties at once disposes of the 
well-known difficulties which pressed on all theories that imposed on the aether 
the quality of solidity. If the objection is taken, which has been made against the 
ordinary vortex-atom theory of matter—that a perfect fluid is a mathematical 
abstraction which does not exist in nature, and the objective existence of which has 
not been shown to be possible,—the conclusive reply is at hand that the I'otatiomd 
elasticity with which the medium is here endowed effectually prevents any slip or 
breach such as would be the point of failure of a simple fluid medium without some 
special quality to ensure continuity of motion. On this head it will be sufficient to 
refer to some remarks of Sir G. G. Stokes'^" on a cognate topic. If therefore it 
is objected that we have no experience of a medium whose elasticity depends 
on rotation and not on distortion, the reply is that we can form no notion of the 
structure of a continuous frictionless fluid medium, unless we endow it with just some 
such elastic property in order to maintain its continuity. 
The idea of representing mag;netic force in the equations of electrodynamics by the 
velocity of the electric medium has been tried already, for example by Heaviside and 
by SoMMERFELD, not to mention Euler. The objection however has been taken by 
Boltzmann and also by yon Helmholtz that it would be impossible on such a 
theory for a body to acquire a charge of electricity. A cardinal feature in the 
electrical development of the present theory is on the other hand the conception of 
intrinsic rotational strain constituting electric charge, which can be associated with an 
atom or with an electric conductor, and which cannot be discharged without rupture 
of tlie continuity of the medium. The conception of an unchanging configuration 
which can exist in the present rotational lether is limited to a vortex ring with such 
associated intrinsic strain : this is accordingly our specification of an atom. The 
elastic effect of convection through the medium of an atom thus charged is equivalent 
to that of a twist round its line of movement: such a twist is thus a physical element 
of an electric current. 
113. The chief result of the discussion is that a rotationally elastic fluid mther 
gives a complete account of the phenomena of optical transmission, reflexion, and 
refraction, in isotropic and crystalline media, coinciding in fact formally in its wider 
features with the electric theory of light ; and that it gives a complete account of 
* Sir G. G. Stoke.s, “ Oil tlie Ooustitation of the Liiuiiiiiferous MElier,” ‘ Pliil. Mag..’ 1848, 
‘ Collected Pajiers,’ vol. 2, p. 11. 
