there by slipping the end of the key under the head of the screw
provided for that purpose. The other operator can then proceed to send
his message.

Those who desire to practice telegraphy should learn the Morse
telegraphic code.


MAGNETIC FIGURES.

By arranging the coil so as to form an electro-magnet, as before
described, and holding the magnet under a plate of glass sprinkled
with fine iron filings, as shown in Fig. 15, and then sending a
current through the magnet, at the same time jarring the glass by
striking it with a lead pencil, a magnetic figure will be formed which
is sometimes called the magnetic spectrum. By connecting the terminals
of the coils diagonally with each other, and connecting the remaining
terminals with the battery, two like poles will be formed, and the
magnetic figures will have an entirely different appearance, owing to
the repulsion between the two like polarities. Different figures may
be produced by using the solenoids without the iron cores.


EXPERIMENT SHOWING THE CURRENT.

By removing the coil, A, from beneath the compass, E, and connecting
the ends of the transverse wire, a' a', with the battery Fig. 16, then
lifting the plates of the battery out of the solution and allowing the
needle to come to rest, it will be found upon inserting the plates of
the battery in the solution, very gradually, that the deflection of