(Located at http://library.advanced.org/27887/gather/fundamentals/telegraphy.shtml)
Today, most long-distance communication signals are transmitted by communication satellites, broadcasting antennas and coaxial and fiber optic cables. The telegraph is the ancestor of all these devices.
Telegraphs were the first message sending devices that utilized the relationship between magnetism and electricity. Telegraphs enabled people to communicate efficiently and quickly over long distances, and were a significant improvement over mail and other communication methods available at the time.
In the 1790s an Italian Scientist named Alessandro Vota invented the electrochemical cell, which made a steady source of electric current available. In 1920 Hans Christian Oersted, a Danish physicist, discovered that a magnetized needle moves under the influence of an electric current. A British electrician named William Sturgeon further developed this idea and invented the electromagnet in 1825.
Three men used these discoveries to develop telegraphs and commercial applications for them.
The First Telegraphs
The telegraph is a device in which current is varied systematically according to a code. William F. Cooke and Charles Wheatstone were two physicists who worked together in Great Britain. The Cooke and Wheatstone telegraph was patented in 1837, using the principle of electromagnetism.
The receiving instrument consisted of five to six magnetic needles mounted vertically onto a dial where letters of the alphabet were printed. There was a separate wire and a coil serving as an electromagnet which controlled each needle. A magnetic field is produced in the coil when an electric current is passed through one of the wires, causing the needles to move. By pointing 2 needles towards the same letter at the same time, the letters were signaled. In 1845, a single needle version was patented, and was used in Great Britain till 1870.
The Morse Telegraph
Samuel F.B. Morse, an American inventor and painter developed another version of a telegraph at around the same time, called the Morse Telegraph. The sending device was a switch called a key, which completed the circuit and allowed the current to flow to a receiving sounder. When the current flows through the sounder, an electromagnet attracts an iron bar, called an armature, and when the armature strikes the magnet, the resulting clicking noise is interpreted according to the "short" and "long" clicks of the armature.
For example, - - - (three "short" clicks followed by three "long" clicks followed by three "short" clicks would be interpreted as SOS. With each click, an instrument attached to the armature also embossed the code on a strip of paper, creating a record of the transmission. Use the Java Applet to the right to translate your messages into Morse Code. Try SOS.
When the key was released, the circuit was broken and no current flowed, causing the electromagnet in the sounder to lose its magnetism. A spring then pulls the bar back into its original position. Morse also developed a relay device to lengthen the distance over which messages could be sent.
Throughout the years, the basic principle of the Morse telegraph has not changed, but much was done to improve this service.
In the late 1890s and early 1900s, devices to send and receive messages in printed form were developed.
During the same period a method of sending messages by means of a paper tape punched with holes was introduced which led to the invention of the teleprinters. These machines were the ancestors of the telex machines, some of which are still in use today. In the late 1920s, teleprinters were gradually adopted by many organizations since they were a reliable method of sending information.
Telegraphs were considered advanced technology in their time and only a select few could actually afford to use them frequently. In fact, if an ordinary person received a telegraph, it was often perceived that it might be bad luck since a telegraph message was often sent to family members when someone had died.
But as technology improved, telegraphs were gradually replaced by more efficient and faster communication devices such as computers and communication satellites, which can also process many types of information. However, the telegraph is still the basis of many of our modern devices, as well as those yet to come. Samuel Morse and many of the early inventors would be amazed today if they could see the results of the legacy they created.
How to Make Your Own Simple Telegraph
Nail the small block of wood and the T-shaped piece of tin onto the large piece of wood as shown in the diagram. This will be the base of the telegraph.
To make the sounder, hammer the 2 steel nails into the other end of the base, wrapping the insulated wire around the nails to form coils.
Connect the coils to the battery with one end of the wire, leaving the other end free to connect to the key.
Also hammer the bent aluminum nail next to, but not touching the T-shaped tin.
Next is the key. Mount the thin metal strip onto the other small wooden block, pushing two thumbtacks halfway through the key.
Remove the insulation from one of the wires attached to the sounder coils, and wrap this end around the tacks and press down.
Bend the other end of the key upwards about half an inch, pressing the third thumbtack under the raised end.
Remove the insulation from both ends of a wire, and connect the battery to this thumbtack on the key.
When pressed, the key should touch the thumbtack, and it ought to spring back up when released.
Electricity flows when the key is touched to the tack, the current flow cause the electromagnets to pull the metal T down, making a clicking sound.
When the key is released, the current flow is stemmed, and the metal T springs back up, striking the aluminum nail creating another clicking sound. These represent the dots and dashes of the Morse code.