“i’ll Put A Girdle Round The Earth In Forty Minutes”

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A thankful but somewhat exhausted Cyrus Field hurried back to England to see how his British colleagues were faring They were making fine progress, spinning out cable at a rate that has seldom been matched since, and ought not to have been attempted then. Largely because Field had promised his backers that the telegraph would start working in 1857, specifications had been sent out to the manufacturers even before the board of management had been set up, and the production of the cable in the short time of six months was a remarkable performance. It involved drawing and spinning 335,000 miles of iron and copper wire and covering that with goo,ooo miles of tarred hemp to form a cable 2,500 miles long. (The actual distance from Ireland to Newfoundland is about 500 miles less than this, but the extra length was needed for slack in paying out and to allow lor possible losses.)

The company’s engineers were not helped by streams of advice and criticism from outside experts, such as the astronomer royal, Sir George Airy, who stated dogmatically that “it was a mathematical impossibility to submerge the cable in safety at so great a depth, and if it were possible, no signals could be transmitted through so great a length.…” When distinguished scientists made such fools of themselves, it is easy to excuse the numerous inventors who wrote to Bright with proposals based on the ancient fallacy that heavy objects did not sink to the sea bed, but eventually came to rest at a level where their density was matched by that of the surrounding water. There is, ol course, no truth in this idea, for water is so nearly incompressible that even at the greatest depths encountered in the ocean its density is only very slightly greater than at sea level.

Some of the hopeful inventors wished to suspend the cable in mid-ocean by underwater parachutes or balloons; others even more optimistically wanted to connect it to a string of floating call boxes across the Atlantic, so that ships could keep in touch with land as they crossed from concilient to continent. Whether they were crazy or not, Charles Bright replied politely to all these proposals, few of which were inhibited by the slightest practical knowledge of the océanographie and telegraphic facts of life.

The Atlantic Telegraph Company, in any event, had little need for outside help. On its own board of directors was a scientific genius (and for once (he word is not misapplied) who was later to do more than any man to save the lost cause of submarine telegraphy and to retrieve the company’s fortunes.

William Thomson, Lord Kelvin, was not the greatest scientist of the nineteenth century; on any reasonable list, lie must come below Darwin and Maxwell. Mut it is probable that he was the most famous man of science of his age, the one whom the general public chiefly identified with the astonishing inventions and technical advances of the era.

In this, public opinion was correct, lor Thomson was a unique bridge between the laboratory and the world of industry. He was an “applied scientist” par excellence, using his wonderful insight to solve urgent practical problems. Yet he was very much more than this, being also one of the greatest ol mathematical physicists. The range ol his interests and activities was enormous; the multiplication ol knowledge that has taken place since his time makes it impossible that we will see his like again. It would not be unfair to say that if one took half the talents of Einstein and half the talents of Edison, and succeeded in fusing such incompatible gifts into a single person, the result would be rather like William Thomson.

Thomson became involved in the telegraph story as a result of his investigations into what are known as transient electric currents. What happens, he asked himself in 1853, when a battery is connected up to a circuit, in the minute interval of time before the current settles down to its steady value? At one moment nothing is happening; a fraction of a second later, a current ol some definite amount is flowing. The problem was to discover what took place during the transition period, which is seldom as much as a hundredth of a second in duration, and is usually very much shorter.

Nothing could have seemed of less practical importance. Yet these studies led directly to the understanding of all electrical communication, and, some thirty years later, to the discovery of radio waves.

Thomson began to investigate the behavior of telegraph cables. It is possible to understand his main results, and to appreciate their importance, without any knowledge of the mathematics he used to obtain them. Putting it briefly, the problem involved was tliis: How long does it take for a signal to reach the far end of a telegraph cable?

It is a common error to imagine that electricity travels along a wire at the speed of light—186,000 miles a second. This is never true, although in some circumstances this velocity can be approached. In most cases, the speed of a current is very much less than that of light—sometimes, indeed, only a tenth or a hundredth of its value.

This slowing-down is due to the electrical capacity of the line. A telegraph cable behaves very much like a hose pipe; it takes a certain amount of electricity to “fill it up” before there is any appreciable result at the other end.