Paragraphs on Telegraph | Communication | Computer Science

A telegraph can be defined as any device or system that allows or facilitates the transmission of in­formation by coded signals over some distance.

The word telegraph is derived from the Greek words ‘tele’ meaning ‘distant’ and ‘graphein’ meaning ‘to write’. It came into existence at the end of the 18th century to describe an optical semaphore system developed in France. Before the telegraph (that is sent over wires today) was invented, other means were being utilised to transmit information over short dis­tances.

These included use of media such as smoke, fire, drums and reflected rays of the Sun. Visual signals given by flags and torches were used for short-range communication and some of these continue to be utilised even today, particularly by some navies in the world. Before the development of the electric telegraph, visual systems were used to convey messages over distances by means of variable displays.

However, the serious developments in telegraphy came about when electric telegraphy was employed. This resulted from the scientific revolution that took place in the 18th/l9th century in the field of electricity. A key development that really spurred the development of telegraphy and that took place at this time was the invention of the voltaic cell in 1800 by the Ital­ian Alessandro Volta.

This made it possible to power electric devices in a more effective manner using low voltages and high currents instead of the previous methods of producing electricity using frictional generation of static electricity, which lead to high voltages and low currents.

However, because of se­vere losses in transmission wires, particularly in bad weather, operations were limited to relatively short distances. Application of the battery to telegraphy was made possible by further developments in the sci­ence of electromagnetism.

Hans Christian Oersted of Denmark discovered in 1820 that a magnetic nee­dle could be deflected by a wire carrying an electric current and in 1825 William Sturgeon in Britain dis­covered the multi-turn electromagnet. In 1831, Michael Faraday and Joseph Henry of the US refined the science of electromagnetism sufficiently to make it possible to design practical electromagnetic devices.

In 1837, Sir William Fothergill Cooke and Sir Charles Wheatstone obtained a patent on a telegraph system that used six wires and actuated five needle pointers connected to five galvanoscopes at the receiving end. If currents were sent through the proper wires the needles could be made to point to specific letters and numbers on their mounting plates. This was probably the first practical application of the electric telegraph.

In 1832, a momentous event in the history of the electric telegraph took place. The perpetrator of this historic event was a professor of painting and sculpture at what later became known as New York University. The name of this professor was Samuel F.B. Morse.

Morse became interested in the possibility of electric telegraphy and made sketches of ideas for such systems. In 1835, he propounded a system of dots and dashes to represent letters and numbers. In 1837, he was granted a patent on an electromagnetic telegraph. His original transmitter incorporated a device called a portarule, which employed molded type with built-in dots and dashes.

The type could be moved through a mechanism in such a manner that the dots and dashes would make and break the contact between the battery and the wire to the receiver. The receiver embossed the dots and dashes on an unwinding strip of paper that passed under a stylus.

The stylus was actuated by an electromagnet turned on and off by signals from the transmitter. One must marvel at the technical capability of a professor of painting and sculpture.

Morse formed a partnership with Alfred Vail, a clever mechanic who is credited with many contri­butions to the Morse system.

Among these are the replacement of the portarule transmitter by a single make-and-break key, the refinement of the Morse Code so that the shortest code sequences were as­signed to the most frequently occurring letters and the improvement of the mechanical design of all the system components.

The first demonstration of the system by Morse was conducted for his friends at his workplace in 1837. In 1843, Morse obtained financial support from the US Government to build a demonstration telegraph system, 60 kilometers (35 miles) long between Washington DC and Baltimore.

Wires were attached by glass insulators to poles alongside a railroad. The system was completed and public use initiated on 24th May, 1844 with transmission of the message, “What hath God wrought!”

In the next phase of development of the telegraph, the American Morse Code came under the scan­ner.

In Europe, it was felt to be inadequate for the transmission of much non-English text because it lacked letters with diacritical marks. Therefore, a new variant was developed and adopted in 1851, which became known as the International Morse Code, for use in cables, for land telephone lines (ex­cept in America) and later for wireless telegraphy.

Except for some minor improvements in 1938, the International Morse Code remained unchanged and is still used in radio communications. New technol­ogy and devices led to a continual evolution of the telegraph industry starting in the latter half of the 19th century and all of the twentieth century.

By 1856, the register in the Morse system was replaced by a sounder, and the code was transcribed directly from the sounds by the operator.

In 1871, J.B. Stearns of the US completed refinement of the duplex transmission system originated in Germany by Wilhelm Ginti, which allowed the same line to be used simultaneously for sending and receiving, thus doubling its capacity.

This was further improved by the American inventor Thomas Alva Edison, who patented a quadraplex telegraph system in 1874 that permitted the simultaneous transmission of two signals in each direction on a single line.

In 1871, Jean-Maurice-Emile Baudot in France devised a system for multiplexing a single line among a number of simultaneous users. This was done by using a distribu­tor consisting of a stationary face plate containing concentric circular copper rings that were swept by brushes mounted on a rotating assembly.

The face plate was divided into sectors depending upon the number of users. Each sector could produce five on or off connections that represented a transmitted letter or symbol. The on/off connections were referred to as marks or spaces—in modern terminology, binary digits or bits, consisting of ones and zeros—and the 32 possible symbols that they encoded came to be known as the Baudot Code.

In the Baudot system, the transmitter and receiver had to be oper­ated in synchronization so that the correct transmitter and receiver were connected at the same time. The first system used manual transmission, but this was soon replaced with perforated tape. Variations of this system were used well into the 20th century. It was the forerunner of what is known today as time-division multiplexing.

During this time of rapid change in the telegraph industry, a new device, the telephone, was patented in 1876 by Alexander Graham Bell. Most people would say that Alexander Graham Bell was the inventor of the telephone, but, the claimants of being the inven­tor of the telephone are many.

We shall next look at this device as well as at some of these claimants and their claims. Of course, it will be realised immediately that the number of people involved in the invention of the telephone as we know it today, is very large.