battery of 25 Leclanche cells, the other pole being connected with one
terminal of a reverser, the second terminal of which is connected to the
other terminal of the spiral.

Now, if this very small spiral which is in circuit with the galvanometer
and a reverser be placed parallel to the center of spiral C, a very
large deflection will be seen on the galvanometer scale; this will
gradually diminish as the smaller spiral is passed slowly over the face
of the larger, until on nearing the edge of the latter the smaller
spiral will cease to be affected by the inductive lines of force from
spiral C, and consequently the galvanometer indicates no deflection. But
if this smaller spiral be placed at a different angle to the larger
one, it is, as you observe by the deflection of the galvanometer, again
affected. This experiment is analogous to the one illustrated by diagram
6, which represents the result of an experiment made to ascertain the
relative strength of capability or producing inductive effects of
different parts of a straight electro-magnet.

A, Fig. 1, represents the iron core, PP the primary coil, connected
at pleasure to one Grove cell, B, by means of the key, K; S, a small
secondary coil free to move along the primary coil while in circuit with
the galvanometer, G. The relative strength of any particular spot can be
obtained by moving the coil, S, exactly over the required position. The
small secondary coil is only cut at right angles when it is placed in
the center of the magnet, and as it is moved toward either pole so the
lines of force cut it more and more obliquely. From this it would appear
that the results obtained are not purely dependent upon the strength of
the portion of the magnet over which the secondary coil is placed, but
principally upon the angle at which the lines of force cut the coil so
placed. It does not follow, therefore, that the center of the magnet is