applied to Electric Currents. 347 
be moved in a direction contrary to that of the current, so that 
there will be an induced current in the opposite direction to the 
primary one. 
If there were no resistance to the motion of the particles, the 
induced current would be equal and opposite to the primary one, 
and would continue as long as the primary current lasted, so that 
it would prevent all action “of the primary current at a distance. 
If there is a resistance to the induced current, its particles act 
upon the vortices beyond them, and transmit the motion of rota- 
tion to them, till at last all the vortices in the medium are set in 
motion with such velocities of rotation that the particles between 
them have no motion except that of rotation, and do not produce 
currents. 
In the transmission of the motion from one vortex to another, 
there arises a force between the particles and the vortices, by 
which the particles are pressed in one direction and the vortices 
in the opposite direction, We call the force acting on the par- 
ticles the electromotive force. The reaction on the vortices is 
equal and opposite, so that the electromotive force cannot move 
any part of the medium as a whole, it can only produce currents. 
When the primary current is stopped, the electromotive forces 
all act in the opposite direction, 
(7) When an electric current or a magnet is moved in pre- 
sence of a conductor, the velocity of rotation of the vortices in 
any part of the field is altered by that motion. ‘The force by 
which the proper amount of rotation is transmitted to each vor- 
tex, constitutes in this case also an electromotive force, and, if 
permitted, will produce currents. 
(8) When a conductor is moved in a field of magnetic force, 
the vortices in it and in its neighbourhood are moved out of 
their places, and are changed in form, The force arising from 
these changes constitutes the electromotive force on a moving 
conductor, and is found by calculation to correspond with that 
determined by experiment. 
We have now shown in what way electro-magnetic phenomena 
may be imitated by an imaginary system of molecular vortices, 
Those who have been already inclined to adopt an hypothesis of 
this kind, will find here the conditions which must be fulfilled in 
order to give it mathematical coherence, and a comparison, so 
far satisfactory, between its necessary results and known facts, 
Those who look in a different direction for the explanation of the 
facts, may be able to compare this theory with that of the exist- 
ence of currents flowing freely through bodies, and with that 
which supposes electricity to act at a distance with a foree de- 
pending on its velocity, and therefore not subject to the law of 
conservation of energy. 
