Joseph John Thomson

“ The magnetic force diminishes very rapidly as we recede from the surface of the sphere. In this case the total current parallel to the axis of inside the sphere is finite, for this by equation (2) equals
So that if the sphere is placed in a magnetic field the force acting upon it is the same as that on a current . When the sphere is moving with a uniform velocity , equations (3) become
whence
where is the velocity of propagation of electrodynamic action through the dielectric. ”

“ If is the velocity of the æther, the electric displacement at right angles to the planes, the magnetic force between the planes will be parallel to , and equal to ; or if is the surface-density of the electrification on the planes , the magnetic force vanishes except between the planes, so that on crossing the positively electrified surface there is an increase in the magnetic force parallel to equal to . ”

“ The first of these corresponds to the well-known expression for the electromotive force on a conductor moving in a magnetic field; the second is the mechanical force on a current in a magnetic field plus the term . ”