How the telegraph works
A very simple telegraph has four parts: a battery that provides electricity, a telegraph key for sending signals, an electromagnetic sounder at the receiving end, and a piece of wire connecting the sender and receiver.
When the telegraph key is pressed down, it completes an electric circuit, and current flows over the wire to the receiver. There, the current travels through a small electromagnet, a coil of wire wrapped around an iron core. This produces an electromagnetic force that pulls down the sounder with a click. When the key is released, the current stops, and the sounder snaps up with another click.
Telegraph messages are sent by code in which letters, numbers, and punctuation marks are represented by dots and dashes-long or short intervals between clicks. In the past, a telegraph operator would tap out messages letter by letter. And operator at the receiving end would listen for the incoming message and translate it back into words. Today, however, machines automatically translate messages into the signal code and back again. And the telegraph system of today are far more complex then the simple one described here.
Sending a telegram:
To send a telegram you may hand deliver or telephone your message to a telegraph office. There, an operator enters the message into a computer, which then translates it into code and routes it to its destination. And the receiving end, machines translate the encoded message back into words and print it out. The telegraph office may hand deliver or telephone the message to the person receiving it.
A telegraph message may travel in several ways. Traditionally, the ter "telegram" has referred to a message sent over wires strung overland or buried underground. "Cable-gram" refers to a message sent abroad oversea cables. They travel by high-frequency radio-waves, which in some cases bounce off communication satellites.
Development of the telegraph: the development of the telegraph depended on a number of discoveries in electricity, in particular the study if the magnetic effects of electrical currents. In 1820, Hans Christian Oerstad, a Danish scientist, observed that electrical currents passing through a wire produced and electromagnetic field strong enough to turn a compass needle. A few years later, William Sturgeon of Britain developed the first electromagnet. These various discoveries led to the development of a practical telegraph system.