176 JAMES CLEUK MAXWELL 



" A theory of molecular vortices, which I worked out at con- 

 siderable length, was published in the /V7. J/<///. for March, 

 April, and May, 18fjl ; Jan. and Feb., 18i2. 



44 1 think we have good evidence for the opinion that some 

 phenomenon of rotation is going on in the magnetic field, that 

 this rot.it ion is performed by a great number of very small 

 portions of matter, each rotating on its own axis, this axis 

 being parallel to the direction of the magnetic force, and that 

 the rotations of these different vortices arc-made todeiund on one 

 another by means of some kind of mechanism connecting them. 



44 The attempt which I then made to imagine a working 

 model of this mechanism must be taken for no more than it 

 really is, a demonstration that mechanism, may bj imagined 

 capable of producing a connection mechanically equivalent to 

 the actual connection of the parts of the electro-magnetic field. 

 The problem of determining the mechanism rc<iuircd to 

 establish a given species of connection between the motions of 

 the parts of a system always admits of an infinite number of 

 solutions. Of these, some may be more clumsy or more com- 

 plex than others, but all must satisfy the conditions of 

 mechanism in general. 



44 The following results of the theory, however, are of 

 higher value : 



44 (I) Magnetic force s the effect of the centrifugal force of 

 the vortices. 



"(2) Klectro-magnetic induction of currents is the effect of 

 the forces called into play when the velocity of the vortices is 

 changing. 



44 (3) Electromotive force arises from the stress on the con- 

 necting mechanism. 



44 (4) Electric displacement arises from the elastic yielding 

 of the connecting mechanism.' 1 



In studying this part of Maxwell's work, it must 

 clearly be remembered that he did not look upon the 

 ether as a series of cog-wheels with idle wheels bo- 

 tween, or anything of the kind, lie devised a mechan- 

 ical model of such cogs and idle wheels, the properties 



