raight lines. Gravity, he knows, will not
turn a corner, but exerts its pull along a right line; hence his aim and
effort to ascertain whether electric action ever takes place in curved
lines. This once proved, it would follow that the action is carried on
by means of a medium surrounding the electrified bodies. His experiments
in 1837 reduced, in his opinion, this point of demonstration. He then
found that he could electrify, by induction, an insulated sphere placed
completely in the shadow of a body which screened it from direct action.
He pictured the lines of electric force bending round the edges of the
screen, and reuniting on the other side of it; and he proved that in
many cases the augmentation of the distance between his insulated sphere
and the inducing body, instead of lessening, increased the charge of
the sphere. This he ascribed to the coalescence of the lines of electric
force at some distance behind the screen.

Faraday's theoretic views on this subject have not received general
acceptance, but they drove him to experiment, and experiment with him
was always prolific of results. By suitable arrangements he placed a
metallic sphere in the middle of a large hollow sphere, leaving a space
of something more than half an inch between them. The interior
sphere was insulated, the external one uninsulated. To the former he
communicated a definite charge of electricity. It acted by induction
upon the concave surface of the latter, and he examined how this act of
induction was effected by placing insulators of various kinds between
the two spheres. He tried gases, liquids, and solids, but the solids
alone gave him positive results. He constructed two instruments of the
foregoing description, equal in size and similar in form. The interior
sphere of each communicated with the external air by a brass stem ending
in a knob. The apparatus was virtually a Leyden jar, the two coatings of
which were the two spheres, with a thick and variable insulator between
them. The amount of charge in each jar was determined by bringing
a proof-plane into contact with its knob and measuring by a torsion
balance the charge taken away. He first charged one of his instruments,
and then dividing the charge with the other, found that when air
intervened in both cases the charge was equally divided. But when
shellac, sulphur, or spermaceti was interposed between the two spheres
of one jar, while air occupied this interval in the other, the