every magnet and every
electrified body. On this point he says, Art. 3263:[34] "To acknowledge
the action in curved lines seems to me to imply at once that the lines
have a physical existence. It may be the vibration of the hypothetical
Aether, or a state of tension of that Aether equivalent to either a
dynamic or static condition."

Par. 3277: "I conceive that when a magnet is in free space, there is
such a medium, magnetically speaking, around it. That a vacuum has its
own magnetic relations of attractions and repulsions is manifest from
former experimental results (2787). What that surrounding magnetic
medium deprived of all material substance may be, I cannot tell, perhaps
the Aether."

It was, however, left for Clerk Maxwell to develop the idea as to their
physical character, and this he did in his paper on "Physical Lines of
Force," _Phil. Mag._, 1861. He had previously written a paper on
"Faraday's Lines of Force," delivered to the Cambridge Phil. Society in
1855 and 1856, but his more matured conception of Faraday's Lines of
Force was given in the later article.

What Maxwell did was to conceive a physical theory of electricity and
magnetism, by which electrified and magnetized bodies could act upon
each other by means of the stress or strain of some medium, which
existed in the space surrounding these bodies. Now Faraday looked upon
electro-static and magnetic induction as always taking place along
curved lines. These lines may be conceived as atoms or molecules
starting from the poles of a magnet, and acting on all bodies in the
electro-magnetic field. These atoms or molecules, joined together in a
definite manner, tend to shorten in the direction of their length, that
is to say, there is a tension along the lines of force while at the same
time they swell out laterally or sideways. Thus there is a tension along
the lines of force, and a pressure at right angles to them owing to
their bulging out sideways. Maxwell used as an illustration of the
tension and pressure, the contraction and thickening of a muscle. As the
fibres of the muscle contract, and the arm or leg is drawn up, the
muscle swells in its centre outwardly, and so thickens. Thus there would
be a tension along the muscle, and a pressure at right angles to it,
which would cause any body placed on it to move away from it, owing to
the pressure of the contracted muscle.

In the conception of an aetherial atom (Art. 44) drawn purely from
observat