162 Prof. Maxwell on the Theory of Molecular Vortices 
the lines of force as something real, and as indicating something 
more than the mere resultant of two forces, whose seat of action 
is at a distance, and which do not exist there at all until a mag- 
_net is placed in that part of the field. We are dissatisfied with 
/ the explanation founded on the hypothesis of attractive and 
repellent forces directed towards the magnetic poles, even though 
we may have satisfied ourselves that the phenomenon is in strict 
accordance with that hypothesis, and we cannot help thinking 
_ that in every place where we find these lines of force, some phy- 
sical state or action must exist in sufficient energy to produce the 
actual phenomena. 
My object in this paper is to clear the way for speculation in 
this direction, by investigating the mechanical results of certain 
states of tension and motion in a medium, and comparing these 
with the observed phenomena of magnetism and electricity. By — 
pointing out the mechanical consequences of such hypotheses, 1 
hope to be of some use to those who consider the phenomena as 
due to the action of a medium, but are in doubt as to the relation 
of this hypothesis to the experimental laws already established, 
which have generally been expressed in the language of other 
hypotheses. 
I have in a former paper* endeavoured to lay before the mind 
of the geometer a clear conception of the relation of the lines of 
force to the space in which they are traced. By making use of 
the conception of currents in a fluid, I showed how to draw lines 
of force, which should indicate by their number the amount of 
force, so that each line may be called a unit-line of force (see 
Faraday’s ‘ Researches,’ 3122) ; and I have investigated the path 
of the lines where they pass from one medium to another. 
In the same paper I have found the geometrical significance 
of the “ Electrotonic State,” and have shown how to deduce the 
mathematical relations between the electrotonic state, magnetism, 
electric currents, and the electromotive force, using mechanical 
illustrations to assist the imagination, but not to account for the 
phenomena. 
I propose now to examine magnetic phenomena from a mecha- 
nical point of view, and to determine what tensions in, or motions 
of, a medium are capable of producing the mechanical pheno- 
mena observed. If, by the same hypothesis, we can connect the 
phenomena of magnetic attraction with electromagnetic phe- 
nomena and with those of induced currents, we shall have found a 
theory which, if not true, can only be proved to be erroneous by 
experiments which will greatly enlarge our knowledge of this 
part of physics. 
* See a paper “ On Faraday’s Lines of Force,’’ Cambridge Philosophical 
Transactions, vol. x. part 1. 
