movable circuit supported by silk and with means of adjusting the
contacts. The rectangles or circles are about two inches in their
extreme dimension. Horizontal and vertical astatic system are also
used--Figs. 18, 18a. The apparatus may be used with either the
horizontal or vertical lantern.

[Illustration: Fig. 16. Fig. 17.]

[Illustration: Fig. 18. Fig. 18a.]

If the rectangle or circle is suspended and a magnet brought near it
when the current passes, the loop will be attracted or repelled, as
the law requires. The experiments usually performed with De la Rive's
floating battery may be exhibited.

The great similarity between the loop and the magnet may be shown by
comparing the fields above (Figs. 14b, 14c) with the actual fields
of two bar magnets, Figs. 19, 19a.

It will be noticed that the lines in Fig. 19, where unlike poles are
opposite, are gathered together as in Fig. 14b,--where the N end of
the magnet faces the S side of the magnetic shell; and that in 19a,
where two norths face, the line of repulsion has the same general
character as in 14c, in which the N end of the magnet faces the N
side of the shell.

[Illustration: Fig. 19.]

[Illustration: Fig. 19a.]