Current at receiving end



Fig. 4.16 Same as 4.15 but So the cause of the change in current between the transmitting and for a longer line.

receiving ends was identified but it was still not known how much the capacitance contributed to the deterioration of the signal and what the role of the resistance was. The economic importance of the problem can be appreciated by looking at some further experimental results for even longer cables. The current at the receiving end then became even more spread out (Fig. 4.16(b)). Therefore one had to wait until this broad current form arrived before the next signal could be sent. Even worse, if a dot and dash were sent in succession (Fig. 4.17(a)) the received current form might have looked like the one shown in Fig. 4.17(b). Now one can't even be sure whether one or two signals were sent let alone whether they were dots or dashes. The inevitable conclusion was that the rate of signalling is bound to be considerably slower on long cables than on short ones. If this rate was below about six words per minute then the Atlantic cable was not an economic proposition.

Fig. 4.17 The current measured at opposite ends of a long telegraph wire when a short and a long pulse are sent.

Fig. 4.17 The current measured at opposite ends of a long telegraph wire when a short and a long pulse are sent.

Current at transmitting end

■ Current at receiving end


■ Current at receiving end

The enterprise would not make a profit, no investor would be interested and the project would never get off the ground.

This was the stage reached when William Thomson (later elevated to the peerage as Lord Kelvin) entered the fray. He assumed that each small element of the wire had both a capacitance and a resistance, deduced the corresponding mathematical relationship between voltage and current and then made the generalization to a long cable. In technical language he derived and subsequently solved a partial differential equation. It was a tour de force, a very sophisticated calculation which only a handful of scientists could understand at the time. Some of the conclusions coming out of all that sophistication were quite simple. He found that the so-called retardation (the time one had to wait before the next signal could be sent) depended on the product of resistance and capacitance. Hence for cables of the same construction, retardation was proportional to the square of the length. If a cable with a given length gave a retardation of one tenth of a second then a cable twice as long would give a retardation of four times as much, that is, four tenths of a second, and a cable 10 times as long would give a retardation of 10 seconds. This relationship became known as the 'law of squares'. It also followed from Thomson's calculations that the retardation for overhead lines was much smaller than for submarine or buried cables because the conductors in overhead lines were much farther from each other than those in the cables.

The kind of calculation William Thomson did was the first shot fired in the Second Industrial Revolution although no-one was aware of it at the time. Calculations had of course been done before but they were relatively simple and the reasoning behind them could be understood by those who made the decisions. With Thomson's calculations this was no longer the case. None of those who were concerned with the technical aspects of the cable nor any of those who sat on the Board of Directors of the Atlantic Telegraph Company could understand any part of Thomson's reasoning. It was not their fault. It happened that for the first time in history pure science intervened in matters industrial and the Directors could not possibly perceive that some incomprehensible scribbling on a few sheets of paper had the capability of predict-

Time ing the future performance of the cable. After all, simple experiments followed by simple calculations always sufficed in the past. Why should one suddenly come to the conclusion that a Professor of Natural Philosophy at the University of Glasgow knows better how to solve the problem than the electricians on the job?

Why make theoretical calculations at all in a field of practical significance? It might be necessary to do such things for the motion of heavenly bodies which do not easily lend themselves to experimentation. Theory can explain why Uranus strayed from its orbit but surely in matters of practical significance conclusions have to be drawn from carefully executed measurements. The sensible thing to do is to manufacture the cable, wind it on lots of big coils, put the transmitting apparatus at one end, the receiving apparatus at the other end and send signals along the whole length of the cable. If the rate of transmission of signals is fast enough the cable is OK. If the rate of transmission is not fast enough then the cable must be modified. Surely, by experimentation alone one would eventually arrive at the correct design. This argument is fine but there is a snag. Each experiment of that kind would have cost several hundred thousand pounds, clearly not in the realm of practical possibilities. The decision about the dimensions of the cable to be produced and about the manufacturing process to be followed had to be made in the absence of sufficient experimental evidence. But could one make some relevant experiments by joining together a few of the existing cables which joined Britain to the Continent? That's exactly what E.O.W. Whitehouse, the man who was later in charge of all the electrical engineering problems in the Atlantic cable project, did. He conducted such experiments in 1855, measured the broadening of the pulses, and concluded that Thomson's predictions were wrong. He gave a lecture at the British Association Meeting in Cheltenham in 1856 entitled 'The law of the squares—is it applicable or not to the transmission of signals in submarine circuits.' He concluded:

I believe nature knows no such application of that law and I can only regard it as a fiction of the schools, a forced and violent adaptation of a principle in Physics, good and true under other circumstances, but misapplied here.

Whitehouse felt that he should not go too far in his criticism. The professor's calculations were no doubt correct—somewhere where the principles of physics played a role—but not in this particular practical problem. The expression, 'a fiction of the schools' made it clear what he thought of Thomson's theory.

What was the argument about? It was about design of the cable: what the diameter of the conductor should be and how thick the insulator between the conductors should be. The main disagreement was on the diameter of the conductor. According to Whitehouse the conductor could be thin, comparable with those used in previous cables.

Thomson favoured thicker cables because that was suggested by his calculations. The Board was unanimously in favour of a cable as thin as possible. The reasons were clear enough. The thinner the conductor the cheaper it was. The final decision was in favour of a relatively thin cable which did not please Thomson but he finally agreed that the cable should be able to work at the required speed.

It may be worth mentioning at this stage that Thomson was one of the directors of the Atlantic Telegraph Company. One might be permitted to think that he was elected on the grounds of his superior knowledge of electricity and mathematics, but that assumption would not be borne out by the facts. He was elected a Director by the Scottish shareholders as an eminent man who would be able to represent their interests on the Board. Did the Board of Directors want to involve Thomson in the electrical problems of the cable? Sometimes they grudgingly agreed to consult him but on the whole they did not think that Thomson's science was relevant to the working of the cable. As it happened, Thomson followed the progress of both attempts in 1857 and in 1858, sailing with the Agamemnon, but not in an official capacity. In the words of S. P. Thompson, an early biographer of William Thomson, 'The work which he undertook for it was enormous; the sacrifices he made for it were great. The pecuniary reward was ridiculously small.'

One could write several chapters about the contributions of William Thomson to the cause of the telegraph. I mention here two more of those contributions. He insisted, as a Director of the Company, that the manufacturers of the cable should work to stringent specifications, and he set up the first factory control laboratory that ever existed. Secondly, the device which made possible the reception of signals across the Atlantic (Whitehouse's own apparatus turned out to be not sufficiently sensitive to be able to receive the weak signals) was Thomson's own invention, a mirror galvanometer (similar in principle to that of Gauss and Weber) adapted specially for working on a rolling ship. The last two contributions were quite crucial in being able to use the 1858 cable for the few months it worked, but they were not fundamental. They could have been done by lesser men. Perhaps not in 1858 but certainly within a decade or so.

I contend above that the Second Industrial Revolution started with the work of William Thomson. For that, we need a definition of the First and Second Industrial Revolutions, terms which have been used loosely in the past. My favoured definition is that the First Industrial Revolution replaced muscle power with machinery, and the Second Industrial Revolution, which is still running in our time, is in the process of eliminating the need for brain power.

There is no doubt that scientists did make significant contributions to the development of the machines fuelling the First Industrial Revo lution (e.g. Professor Black, also from Glasgow) but the technologists would have managed on their own. The Second Industrial Revolution is in a quite different category. It came about as a result of a unique blend of interaction between science and technology with occasional government encouragement (the most expensive example being the Manhattan project).

William Thomson was the pioneer in producing the theoretical work crucial for the progress of communications but very soon Maxwell and his disciples took over. I shall discuss their contributions later when coming to wireless telegraphy. It might however be instructive to ask at this stage the question: how important was the work of the leading scientists in the hundred years from 1815 to 1914? What would have happened if three or four dozen of those scientists had died in their infancy? There is no doubt that our lives would be entirely different. We would have no telephone, no radio, no television, no computers, no X-ray diagnosis and no magnetic resonance imaging.12 One may very well contrast this with the influence of great politicians. If in that period all the rulers of Europe and all their Prime Ministers had perished before they assumed office, that would have made only very minor differences in the world. Perhaps the Franco-Prussian war would never have taken place and the First World War might have been fought between different alliances but that is probably all. Those eminent scientists would have made the same discoveries and inventions whoever had been the rulers.

12 No hydrogen bomb either, but that's a separate question.

13 Born as Karl Wilhelm he was one of the younger brothers of Werner von Siemens. He emigrated to England in the 1840s, became naturalized in 1859, was elected a Fellow of the Royal Society in 1862, and was knighted shortly before his death in 1883.

14 It may be worth mentioning here a late arrival (1902) to the network which connected New Zealand, Australia and Canada. Its fame is partly due to the fact that it broke the monopoly of Eastern Telegraph but it also induced Rudyard Kipling to celebrate the event in verse far superior to that written by other telegraph enthusiasts:

Here in the womb of the world, here on the tie-ribs of earth,

Words, and the words of man, flicker and flutter and beat— Warning, sorrow and pain, salutation and mirth—

For a Power troubles the Still that has neither voice nor feet.

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