2: The Electric Telegraph

Two other concepts of computing that have their roots in 18th and 19th century developments are the idea of using pulses of electricity to convey information, and the idea of scanning a picture to convert it into data that can be conveyed through wires, and so, over a century later, used by computers. It is in this latter that Jacquard’s concept of the production of images by programmable machines and the electric telegraph are welded together. We shall begin this section by looking at the idea of conveying information along wires.

The ancient Greeks knew about the static electricity that developed through friction between dissimilar materials such as rubbing silk on a glass rod or amber; in fact the origin of the word electron is to be found in the Greek for amber or “elektron” [ήλεκτρου].¹ Static electricity is that spark you often get from the car door handle on a dry summer’s day and can be of some thousands of volts though of negligible current, thus surprising and stinging one more than doing any appreciable damage. Early scientific experimenters had to make their electricity by spinning balls of glass or other insulators like sulphur, and holding their hands against the spinning glass to produce frictional electricity, which was then conveyed to the experiment by a “conductor”. That electricity could be stored for later use was discovered accidentally by the Dutch experimenter Cuneus in 1746 [Fig.1] when he gave himself a severe electric shock while attempting to electrify water held in a jar.² From this, the Leyden Jar, effectively a “condenser” or very large capacitor, was invented and became the primary means for storing electricity for demonstrations and early experiments in sending currents through long wires. The Leyden Jar is not a battery since it has to have its electric charge produced by an electrical machine which is then stored in the jar, while a battery, invented by the Italian physicist Alessandro Volta in 1800, uses chemical action to generate electric current. Benjamin Franklin discovered that lightning was an electrical discharge from storm clouds into the earth and devised a method for storing it in a Leyden Jar to use this stored electricity in his experiments.³

In 1748, the English scientist William Watson showed that electric current could be conducted through very long wires apparently instantaneously⁴ and in 1753 Charles Morrison (of Scotland), wrote to the Scots Magazine of “An Expeditious Method of Conveying Intelligence” suggesting a means for “transmitting messages by frictional electricity”.⁵

“It is well known to all who are conversant in electrical experiments that the electric power may be propagated along a small wire, from one place to another, without being sensibly abated by the length of its progress; let, then, a set of wires equal in number to the letters of the alphabet be extended horizontally between two given places parallel to each other and each of them about an inch distant from that next to it.”⁶

A metallic ball would then be suspended from each wire and immediately below that were to be placed small pieces of paper with the letters of the alphabet written on them. On the discharge of an electric current into one of the wires at a distant place the piece of paper below the metallic ball would be raised up indicating the letter being communicated. A system of this type was implemented by George Louis LeSage of Geneva in 1774⁷ but, as it required separate wires for each character to be transmitted and with the difficulty of controlling the discharge of frictional electricity it failed to yield useful results.⁸

Joseph Bozolus⁹ suggested employing the Leyden jar to convey intelligence in 1767. Two wires were to be laid underground and at each terminus to be brought to the inner and outer coatings of the Leyden jar. By discharging sparks into one terminus they could be seen at the other terminus and a message could be transmitted by a predetermined code.¹⁰ This appears to be the first suggestion that sparks (or pulses) of electricity could be used as a method of encoding information, but it wasn’t taken any further until 1795 when Tiberius Cavallo suggested that “by sending a number of … sparks at different intervals of time according to a settled plan, any sort of intelligence might be conveyed instantaneously from” place to place through an insulated wire.¹¹ With this suggestion, he introduced the idea of communicating by using pulses whose timing might be understood as a coded sequence of signals representing letters. Numerous experiments in electrical signalling followed over the next twenty five years, but little advance was made towards a receiver that was both reliable and easily read.

In 1823 Francis Ronalds published a small booklet on his electric telegraph. Having determined that an electric current would travel at such speed, along a wire of 8 miles in length, that the start and receipt of the signal were indistinguishable, in 1816, he invented a telegraph which transmitted signals by means of synchronously rotating dials at each station; it was the first such machine to employ this technique.¹² A pith ball electrometer was set before each clock. The pith balls at each end of the communicating wires were charged from a Leyden jar and, as the command to be sent became visible in the face of the sending clock, it was discharged. On the discharge of the battery the pith balls would collapse to indicate the words in the receiving clock that matched the words in the sending clock (always supposing that the two clocks were in synchrony). Letters, numbers and, by the use of a specially prepared “dictionary”, whole sentences could be transmitted in this manner. Ronalds used a “Prepare” signal of greater charge, which caused the pith balls to stand out further from the face of the clocks. It was to be understood that this “Prepare” would discharge only when the letter “A”, the number “1” and the command “Prepare” were in the sending aperture and by this means the receiving aperture could be moved to be over the same characters on the receiving clock, thus synchronising the apparatus. Ultimately his system would have faced the problem of having to be constantly resynchronised. It wasn’t until the 1840s that a means for doing this was realized.

Both the French savant Andre-Marie Ampere and the English scientist Wollaston explained this electro-magnetic effect on the magnetized needle by supposing “an electro-magnetic current passing around the axis of the conjunctive wire, its direction depending on that of the electric current, or upon the poles of the battery with which it is connected”.¹³ This led Ampere to invent the electromagnet.¹⁴ He also proposed a needle telegraph using as many conducting wires and needles “as there are letters”. By connecting the communicating wires of the telegraph to any letter in sequence individual needles may be made to indicate their letters.¹⁵

Johann Schweiger invented a means of multiplying the deflection of a magnetised needle under the power of an electric current. By winding an insulated wire a limited number of times (so as not to defeat the effect by increasing the resistance to the current by the length of the wire) onto a rectangular former and placing it around the axis of the needle he found that he could make an appreciable difference in the amount of deflection bringing it towards ninety degrees.¹⁶ This device forms the basis of the measuring instrument known as a galvanometer (or voltmeter). But more importantly it allowed the effect of a current transmitted some distance to be multiplied so as to produce the distinct deflections of a needle necessary to indicate the presence or absence of that current. [Fig.3]

William Fothergill Cooke saw Schilling’s apparatus in Heidelberg, Germany, in 1836¹⁷ and he and Charles Wheatstone subsequently employed a similar technique in their telegraph systems.¹⁸ Their first apparatus was a five-needle telegraph in which 6 wires (five signal and one ground-return) controlled the positions of the five needles according to the way a set of key were pressed. Depending on which character was being transmitted two of the needles would point to it on the front face of the frame.¹⁹ [Figs.4 & 5] This version was used on the Birmingham-London railway.

Cooke and Wheatstone further developed their telegraphs producing both two-needle and single-needle [Fig.7] devices which also used a code for the messages. The single needle apparatus functioned as follows. A pair of magnetized needles borne on the same axis are made to stand vertically, so that “such an arrangement, if the needles are of equal power, has no tendency towards one point of the compass more than another; and, by making what are the lower ends of the needles somewhat heavier than the opposite extremities, the needles, when not under the influence of electric currents, will at once resume their vertical position”.²⁰ One needle then acts “as the visible index”²¹ on the front of the apparatus and the other behind the faceplate has a “multiplier” coil of wire around it which transmits the “telegraphed” deflection of the needle. Thus the needles when under the influence of a current flowing through the “multiplier” coil can be made to point towards specific positions on a circle whose centre is the axis of the needles. An appropriate code is then agreed by the sending and receiving parties in reading the deflections of the needles.

In that one year (1836), three separate versions of a functional electric telegraph were demonstrated. As well as Cooke and Wheatstone’s invention, a system of sending messages using a two-state code was shown by the German, Steinheil, and in America, Samuel Morse presented a telegraph which employed an electromagnet to pull a stylus onto a moving roll of paper-tape²² thereby marking it for the duration of the current. By using a “key” – essentially a rocker switch that could connect and disconnect a battery to the telegraph wire – short and long pulses of current could be sent along the wire to his receiver. [Fig.6] Morse developed a code – of short pulses or “dots”, longer pulses or “dashes” and spaces, during which no current flowed – by which the letters of the alphabet, numbers and other indicators could be telegraphed. The pulses recorded on the tape could then be decoded from a dictionary.

In 1839 the engineer (and bridge builder) Isambard Kingdom Brunel commissioned a network of telegraph stations (using the Wheatstone apparatus) on the Great Western Railway in Britain so that information about trains arriving and departing could be “telegraphed” to the next station.²³ Over the 1840’s and 50’s the telegraph network expanded rapidly along-side the railway lines, assisting the railway companies in co-ordination of their networks.²⁴

All digital information used in modern day computers and data networks is represented in binary numbers (as originally explored by Leibniz, above) and in agreed codes where binary numbers stand for letters of the alphabet (eg, ASCII) or other useful symbols. In digital electronics the binary 0 is represented as a low level of voltage and a 1 is represented as a high level of voltage. For the electricians who invented telegraphy this meant simply using a switch to connect the telegraph to, or disconnect it from, the wire which is exactly what the Morse key did.

While the switch is “on” current flows, yielding a 1, or “true” state in logic, and while it is “off” current does not flow, yielding a 0, or “false” state in logic.

The transistors in a computer chip act as switches permitting or blocking current flow and it is through the representation of logic as states with these transistor switches by which all computing operates.

Thus we can see that the late 18th and 19th century telegraphers provided the link between the binary number system of Leibniz, the notion that a machine could change its character through the substitution of new sets of instructions, represented in both automata and the Jacquard loom, and, through the work of the 19th Century Irish mathematician George Boole,²⁶ that logical propositions could be represented in the binary form and operations carried out on them by mechanical and electronic machines.

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Footnotes

1. Deschanel, A. Privat (1872) Elementary Treatise on Natural Philosophy (tansl. J.D. Everett), London: Blackie and Son, p.506. ↩︎
2. Deschanel, (1872), op cit, p.570. ↩︎
3. Deschanel, (1872), op cit, p.599. ↩︎
4. Mottelay, Paul F. (1922) op cit, p.412. ↩︎
5. see: Scots Magazine. XV, p.73, or Scientific American Supplement, No. 570, Dec. 4th, 1886. or Mottelay, (1922), op cit, p.208. ↩︎
6. Quoted in anon, (n.d.) The Story of the Telegraph, in Adventures in Cybersound, Melbourne: Australian Centre for the Moving Image. ↩︎
7. Ibid. ↩︎
8. Deschanel, (1872), op cit, p.713. ↩︎
9. See THE ELECTRICIAN, AUGUST 4, 1883. 285
   “1767.—Bozolus’s Telegraph.
   Joseph Bozolus, a Jesuit and lecturer on natural philosophy in the College at Rome, was the next to suggest an electric telegraph, and one in which the spark was the active principle. This must have been some time anterior to 1767 as we find it familiarly described in a Latin poem,* published in that year. His proposition was to lay underground two (? insulated) wires between the communicating stations, which may he any distance apart. At both stations the ends of the wires were to be brought close together, without touching, so as to facilitate the passage of a spark. When, under these circumstances, at one end the inner coating of a charged plate, or [Leyden] jar, was connected to one wire. and the outer coating to the other, the discharge would take place through the wires. and manifest itself, at the beak, at the distant end, in the form of a spark. An alphabet of such sparks, Bozolus says, could be arranged with a friend without any diliculty, and a means of communication be thus contrived, which, as tolerably easy, he leaves to each one°s judgment to devise and settle in detail.” ↩︎
10. Mottelay, Paul F. (1922) op cit, p.226. ↩︎
11. Cavallo, Tiberius (1795) Treatise on Electricity, Vol.III, 4th edition, London, pp.285-296. ↩︎
12. Ronalds, Francis, (1823), A Description of An Electrical Telegraph, London: Hunter; and Deschanel, 1872, op cit. ↩︎
13. Brewster, (1821), op cit, p.435. ↩︎
14. Mottelay, (1922), op cit, p.472. ↩︎
15. Brewster, (1821), op cit, p.435. ↩︎
16. Mottelay, (1922), op cit, p.412. ↩︎
17. Mottelay, (1922), op cit, p.422. ↩︎
18. Mottelay, (1922), op cit, p.412. ↩︎
19. Guillemin, Amédée, (1891) Electricity and Magnetism (revised and edited by Silvanus P. Thompson), London: MacMillan & Co., pp.581ff. ↩︎
20. Wilson, George, (1852) Electricity and the Electric Telegraph, London: Longman, Brown, Green and Longman, p.39. ↩︎
21. ibid. ↩︎
22. Deschanel, (1872), op cit, p.715. ↩︎
23. Hyman, Anthony. (1982) Charles Babbage – Pioneer of the Computer. Oxford: Oxford University Press, p.227. ↩︎
24. Woolley, Benjamin (1999) The Bride of Science, London: Macmillan, p.252. ↩︎
25. The automatic telegraph was also known as the “Electric Jacquard” on account of the punched holes in the tape being used to store information. See Ciolek, T. Matthew, Global Networking: a Timeline, 1800-1899 at http://www.ciolek.com/PAPERS/GLOBAL/1800.html ↩︎
26. Boole, George (1854) An Investigation of the Laws of Thought, on which are founded the Mathematical Theories of Logic and Probabilities, London: Walton and Maberly. ↩︎