ON THE LINES OF MAGNETIC FORCE. 
27 
same is the case with the idea of a magnetic fluid or fluids, or with the assumption 
of magnetic centres of action of which the resultants are at the poles, flow the mag- 
netic force is transferred through bodies or through space we know not ; whether the 
result is merely action at a distance, as in the case of gravity ; or by some interme- 
diate agency, as in the cases of light, heat, the electric current, and (as I believe) 
static electric action. The idea of magnetic fluids, as applied by some, or of mag- 
netic centres of action, does not include that of the latter kind of transmission, but 
the idea of lines of force does. Nevertheless, because a particular method of repre- 
senting the forces does not include such a mode of transmission, the latter is not 
therefore disproved ; and that method of representation which harmonizes with it may 
be the most true to nature. The general conclusion of philosophers seems to be, that 
such cases are by far the most numerous, and for my own part, considering the rela- 
tion of a vacuum to the magnetic force and the general character of magnetic phe- 
nomena external to the magnet, I am more inclined to the notion that in the trans- 
mission of the force there is such an action, external to the magnet, than that the 
effects are merely attraction and repulsion at a distance. Such an action may be a 
function of the ether; for it is not at all unlikely that, if there be an ether, it should 
have other uses than simply the conveyance of radiations (2591. 2787.)- Perhaps 
when we are more clearly instructed in this matter, we shall see the source of the con- 
tradictions which are supposed to exist between the results of Coulomb, Harris and 
other philosophers, and find that they are not contradictions in reality, but mere 
differences in degree, dependent upon partial or imperfect views of the phenomena 
and their causes. 
3076. Lines of magnetic force may be recognized, either by their action on a mag- 
netic needle, or on a conducting body moving across them. Each of these actions 
maybe employed also to indicate, either the direction of the line, or the force exerted 
at any given point in it ; and this they do with advantages for the one method or the 
other under particular circumstances. The actions are however very different in their 
nature. The needle shows its results by attractions and repulsions ; the moving con- 
ductor or wire shows it by the production of a current of electricity. The latter is 
an effect entirely unlike that produced on the needle, and due to a different action of 
the forces ; so that it gives a view and a result of properties of the lines of force, such 
as the attractions and repulsions of the needle could never show. For this and other 
reasons I propose to develope and apply the method by a moving conductor on the 
present occasion. 
3077- The general principles of the development of an electric current in a wire 
moving under the influence of magnetic forces, were given on a former occasion, in 
the First and Second Series of these Researches (36. &c.); it will therefore be unneces- 
sary to do more than to call attention, at this time, to the special character of its indi- 
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