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.11] 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 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 Bozolus 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.9 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.10 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.11 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.
Meanwhile, in 1820, the Danish scientist Hans Christian Oersted discovered “the intimate relation existing between electricity and magnetism”.12 His experiment showed that electric current flowing through a wire caused a magnetized needle to turn at right angles to the wire.13 David Brewster described the experiment more fully in his Edinburgh Philosophical Journal. To paraphrase: Oersted placed a straight piece of wire, connecting the positive and negative poles of a battery horizontally above and parallel to a well-suspended magnetic needle, which was allowed to align itself with the earth’s magnetic poles. When a current of electricity flowed through the connecting wire the magnetic needle would deviate from its equilibrium position, rotating through an angle that is proportional to the current flowing though the circuit. Swapping the poles of the battery will reverse the direction of deviation of the needle.14 [Fig.12]
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”.15 This led Ampere to invent the electromagnet.16 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.17
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.18 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.13]
It is with Oersted’s discovery, its explanation by Ampere and Wollaston and the amplification of its effect produced by Schweiger that we are brought to the verge of the electric telegraph. The Russian diplomat Pawel Lwowitch Schilling availed himself of Oersted’s discovery of the electromagnetic effect and its multiplication by Schweiger’s device and in 1832 invented a so-called “deflective telegraph”. His apparatus had two wires and one needle and, by changing the polarity of the connection to the voltaic pile (battery), he could deflect the needle to the left or the right to produce “all necessary signals for a complete correspondence”.19
William Fothergill Cooke saw Schilling’s apparatus in Heidelberg in 183620 and he and Charles Wheatstone subsequently employed a similar technique in their telegraph systems.21 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.22 [Figs.14 & 15] This version was used on the Birmingham-London railway.
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-tape23 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.16] 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.
Cooke and Wheatstone further developed their telegraphs producing both two-needle and single-needle [Fig.17] 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”.24 One needle then acts “as the visible index”25 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 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.26 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.27
In 1844 Morse received US government support to establish a telegraph line between Baltimore and Washington DC. After certain modifications and particularly the development of a “sounder”, which enabled the telegraph operator to decode the message simply by listening, the Morse system became more or less the US and European standard and was also eventually adopted in Britain. [Fig.18]
In the next big development, about 1858, one which had effects right up to modern times, Wheatstone developed a recording technique in which three rows of holes were punched in a paper tape [Fig.16]. The central row were equidistant and permitted a rotating toothed gear to move the tape at a uniform speed. On the outer rows, a dot was represented as an opposite pair of holes and a dash as a pair of obliquely offset holes. This allowed the message to be prepared beforehand and then transmitted automatically, greatly speeding up the number of letters that could be transmitted per second.28 Various improvements of the punched-tape code took place over the following years, culminating in the five-bit code Baudot code which was capable of representing all the letters of the Roman alphabet and the necessary punctuation, including a “space” character. This system went on to be used for inputting data and instructions (programs) into many early modern computers.
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 zero is represented as a low level of voltage and a one 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,29 that logical propositions could be represented in the binary form and operations carried out on them by mechanical and electronic machines.
FOOTNOTES
1 Mottelay, Paul F. (1922) Bibliographical History of Electricity and Magnetism, London: Charles Griffin & Co, p.421.
2 Mottelay, Paul F. (1922) op cit, p.421.
3 Mottelay, Paul F. (1922) op cit, p.412.
4 Mottelay, Paul F. (1922) op cit, p.412.
5 Guillemin, Amédée, (1891) Electricity and Magnetism (revised and edited by Silvanus P. Thompson), London: MacMillan & Co., pp.581ff.
6 Deschanel, A. Privat (1872) Elementary Treatise on Natural Philosophy (tansl. J.D. Everett), London: Blackie and Son, p.715.
7 Wilson, George, (1852) Electricity and the Electric Telegraph, London: Longman, Brown, Green and Longman, p.39.
8 ibid.
9 Hyman, 1982, op cit, p.227.
10 Woolley, Benjamin (1999) The Bride of Science, London: Macmillan, p.252.
11 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
12 Boole, George (1854), An Investigation of the Laws of Thought, on which are founded the Mathematical Theories of Logic and Probabilities, Walton and Maberly, London.
13 Deschanel, op cit, p.506.
14 Deschanel, 1872, op cit, p.570.
15 Deschanel, 1872, op cit, p.599.
16 Ronalds, Francis (1823)A Description of An Electrical Telegraph, London: Hunter; and Deschanel, 1872, op cit, p.585.
17 see: Scots Magazine. XV, p.73, or Scientific American Supplement, No. 570, Dec. 4th, 1886. or Mottelay, 1922, p.208.
18 Quoted in anon, (n.d.) The Story of the Telegraph, in Adventures in Cybersound, Melbourne: Australian Centre for the Moving Image <http://www.acmi.net.au/AIC/TELEGRAPHY_LULA.html>
19 ibid.
20 Deschanel, 1872, op cit, p.713.
21 Mottelay, Paul F. (1922) Bibliographical History of Electricity and Magnetism, London: Charles Griffin & Co, p.226.
22 Cavallo, Tiberius (1795) Treatise on Electricity, Vol.III, 4th edition, London, pp.285-296.
23 Ronalds, op cit, 1823.
24 Mottelay, 1922, op cit, p.452.
25 “[H]e contends that there is always a magnetic circulation around the electric conductor, and that the electric current in accordance with a certain law always exercises determined and similar impressions on the direction of the magnetic needle, even when it does not pass through the needle but near it” [Mottelay, 1922, op cit, p.453-4]. This discovery led eventually to the dynamo and the electric motor and to the concept of electromagnetism sorted out by Clerk Maxwell.
26 Brewster, David, (ed) (1821) Edinburgh Journal of Science, vol.IV, Edinburgh: Blackwood, p.168; and Deschanel, 1872, op cit, p.697.
27 Brewster, 1821, op cit, p.435.
28 Mottelay, 1922, op cit, p.472.
29 Brewster, 1821, op cit, p.435.
30 Mottelay, 1922, op cit, p.412.
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