A telegraph circuit is an electrical circuit attached to a
telegraph. This circuit is incomplete until the telegraph is
connected, allowing for the Morse-code messages by tapping the
circuit closed.
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HOW THEY MADE A MORSE CODE MACHINE
Samuel F.B. Morse and Alfred Vail developed an electric
telegraph which sent pulses of electrical current to control an
electromagnet that was located at the receiving end of the
telegraph wire.
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telephone
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The first of the great uses for electricity, began with the
telegraph invented by Samuel Morse around 1840.