nections.

When you want to telegraph, open the switch of the instrument
you want to send from and close the switch of the instrument
which is to receive the message.

Holding the key down a little while, then letting it up, makes
a "dash," while letting it spring up instantly, makes a "dot."

Practice making dots and dashes. Telegraph the word "cat,"
using the alphabet shown on the next page. Telegraph your own
name; your address.

[Illustration: FIG. 141. Diagram showing how to connect up two
telegraph instruments. The circles on the tables represent the binding
posts of the instruments.]

[Illustration: FIG. 142. Telegraphing across the room.]

Here is the Morse telegraph code in dots and dashes:

LETTERS

A B C D E F G
.- -... .. . -.. . .-. --.

H I J K L M N
.... .. -.-. -.- -- - - -.

O P Q R S T U
. . ..... ..-. . .. ... - ..-

V W X Y Z &
...- .-- .-.. .. .. ... . . ...

NUMERALS

1 2 3 4 5
.--. ..-.. ...-. ....- ---

6 7 8 9 0
...... --.. -.... -..- ----

By using the Morse code, telegraph and cable messages are sent all
over the world in a few seconds. The ability to send messages in this
way arose from the simple discovery that when an electric current
passes around a piece of iron, it turns the iron into a magnet.

HOW A TELEPHONE WORKS. A telephone is much like a delicate and
complicated telegraph in which the vibrations started by your voice
press the "key," and in which the sounder can vibrate swiftly in
response to the electric currents passing through the wire. The "key"
in the telephone is a thin metal disk that vibrates easily, back of
the rubber mouthpiece. Each time an air vibration from your voice
presses against it, it increases the current flowing in the circuit.
And each time the current in the circuit is increased, the disk in the
receiver is pulled down, just as the sounder of a telegraph is pulled
down. So every vibration of the disk back of the mouthpiece causes
a vibration of the disk in the receiver of the other telephone; this
makes the air over it vibrate just as your voice made the mouthpiece
vibrate, and you get the same sound.

To make a difference between slight vibrations and larger ones in
telephones, there are