TRANSACTIONS OF SECTION A. 603 



because the latter never come into actual contact. In a conductor, however, we 

 are to suppose that the atomic elements cau do so. When a current is flowing, a 

 filament and its equivalent hollow stretch between two neighbouring atoms, tbey 

 are pulled into contact, or their motions bring them into contact, the hollow dis- 

 appears, and the rotational filament joins its two ends and sails away as a small 

 neutral vortex ring into the surrounding medium, or returns to its function as an ether 

 cell. The atoms being free are now pulled back to perform a similar operation for other 

 filaments. The result is that the atoms are set into violent vibrations, causing the 

 heating of the conductor. When, howevei', the metal is at absolute zero of tem- 

 perature, there is no motion, the atoms are already in contact, and there is no resist- 

 ance, as the observation of Dewar and Fleming tends to show. Further, as the 

 resistance depends on the communication of motion from molecule to molecule, we 

 should expect the electrical conductivity of a substance to march with its thermal 

 conductivity. Again, on this theory the resistance clearly increases with increase of 

 distance between atoms — i.e., with increase of temperature. On the contrary, in 

 electrolytic conduction the same junction of filament ends is brought about, not by 

 oscillations of molecule to molecule, but by disruption of the molecule and passage 

 of atom to atom. In this case conduction is easier the more easily a molecule is split 

 up, and thus resistance decreases with increase of temperature. To explain the laws 

 of electrolysis it is only necessary to assume that the strengths of all filaments are the 

 same. A similar hypothesis, as we have seen, lies at the basis of J. J. Thomson's 

 explanation of chemical combination, although it is not necessarily the case that 

 we are dealing with the same kind of filaments. It is evident that the theory 

 easily lends itself to his views as to the mechanism of the electric discharge 

 through gases. The modus operandi of the production of the mechanical forcive 

 on a conductor carrying a current iu a magnetic field and of electrodynamic 

 induction is not clear. Probably the full explanation is to be found in the 

 stresses produced in the ether owing to the deformation of the cells by the passage 

 of the filaments through them. The fluid moves according to the equation of con- 

 tinuity without slip, and subject to the surface conditions at the conductors. This 

 motion, however, distorts the cells, and stresses are called into play. Any theory 

 which can explain the mechanical forcives and also Ohm's law, must, on the 

 principles of the conservation of energy, also explain the induction of currents. 



The magnetic rotation of the plane of polarisation of light does not depend on 

 the structure of the ether, or on the magnetic field itself, but is a result of the 

 atomic configuration of the matter in the field modified by the magnetism. It is 

 generally recognised as caused by something in the field rotating round the direc- 

 tion of the magnetic lines of force. Now the vortex atom, as usually pictured, is 

 incapable of exhibiting this property. It is, however, an interesting fact, and one 

 which I hope to demonstrate to this Section during the meeting, that a vortex ring 

 can have two simultaneous and independent cyclic motions — one the ordinary one, 

 and another which is capable of producing just the action on light which shows 

 itself as a rotation of the plane of polarisation. The motion is rather a compli- 

 cated one to describe without a diagram, but an idea of its nature may be obtained 

 by considering the case of a straight cylindrical vortex. The ordinary straight 

 vortex consists, as every one knows, of a cylinder of fluid revolving like a solid, and 

 surrounded by a fluid in irrotational motion. In the core the velocity increases 

 from zero at the axis to a maximum at its surface. Thence it continuously 

 decreases in the outer fluid as the distance increases. Everywhere the motion is 

 in a plane perpendicular to the axis. Let us now consider a quite diflerent kind 

 of vortical motion. Suppose the fluid is flowing along the core like a viscous fluid 

 through a pipe ; the velocity is zero at the surface and a maximum at the axis. 

 Everywhere it is parallel to the axis, the vortex lines are circles in planes perpen- 

 dicvdar to the axis, and concentric with it. Since the velocity at the surface of the 

 core is zero, the surrounding fluid is also at rest. Now superpose this motion on 

 the previous one, and it will be found to be steady. If a short length of this 

 vortex be supposed cut oft', bent into the shape of a circle and the ends joined, we 

 shall have a very rough idea of the compound vortex ring of which I speak. I 



