[Illustration: Fig. 14a.]


FIELDS OF LOOPS AND MAGNETS.

Place now a vertical loop opposite to the pole of a short bar magnet
cemented to the glass plate with the N pole facing it. If the current
passes in one direction the field will be as represented by Fig.
14b; if it is reversed by the commutator, Fig. 14c is an image of
the spectrum. Applying Faraday's second principle, it appears that
attraction results in the first case, and repulsion in the second. The
usual method of stating the fact is, that if you face the loop and the
current circulates from left over to right, the N end of the needle
will be drawn into the loop.

[Illustration: Fig. 14b.]

[Illustration: Fig. 14c.]

It thus becomes evident that the loop is equivalent to a flat steel
plate, one surface of which is N and the other S. Facing the loop if
the current is right handed, the S side is toward you.


TO SHOW THE ACTUAL ATTRACTION AND REPULSION OF A MAGNET BY A "MAGNETIC
SHELL."

Produce the field as before (Fig. 14), carry a suspended magnetic
needle over the field. It will tend to place itself parallel to the
lines of force, with the N pole in such a position that, if the