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Peter Cochrane's Hard Drive 1999 Tube that filled a vacuum I WAS put on the spot recently, and asked to identify the single key invention of the 20th century from which all else followed. Of course, this is fundamentally impossible, because invention is neither a singular nor a solitary pursuit. Everything is related. So after considerable thought I decided to nominate the single most important invention, and chose the triode vacuum tube, or valve, invented in 1915 by DeForest. And the principal reason for my choice? Because for me this marks the beginning of the information technology revolution we enjoy today. Up to this time the performance of telephone networks had been constrained by electromagnetic and mechanical devices. Coast-to-coast telephone calls in America were theoretically possible but wholly impractical with a calculated requirement for copper wires of 0.5 to 1in in diameter. As it was, the telephone network in New York warranted 90ft poles with 50 cross-arms and 12 wires per arm along the entire length of Broadway. The street must have been almost waterproof! Broadcast radio and TV were also fundamentally impossible to realise. Despite the sterling efforts to create amplifiers using the gain of electromechanical coupling, and the generation of radio carrier signals through rotating machinery, it was clear that something fundamentally new was required. The arrival of the first stable device capable of electronic gain (the vacuum tube) had an immediate impact on the long-lines telephone network and saw the establishment of broadcast radio services late in 1919. The first two-way telephone communication between Britain and America was in 1926 from the AT&T Manhattan office and the Post Office in London. The regular public transatlantic service started in 1927, using high-frequency radio with 12 channels. That was only eclipsed in 1956 by TAT1 - the first transatlantic telephone cable with an initial 36 simultaneous speech circuits. At the time, the accountants were concerned by the lack of financial prudence. HF radio already provided 24 channels and the cost of a call was around half a week's wage. So where would the demand come from? By 1986 there were seven cables with a total of 12,000 speech circuits, and six satellites providing 57,000 circuits. When TAT8 was installed the technology had moved on to fibre optics, with 7,680 base circuits on four fibres in one cable. Today systems are being planned with capacities 1,000 times the capacity of TAT8 and five million that of TAT1. In the year I was born, Shockley, Bardeen and Brattain invented the transistor, and although the physics are fundamentally different, many of the concepts pioneered by DeForest are evident. But more important, the electronic markets and technologies to make this invention possible were established by 32 years of prior vacuum tube development. Today vacuum tubes are rare, while 10,000 transistors are manufactured for every man woman and child on the planet every day. So the child really killed the parent - but what a parent! Deforest's legacy to mankind is enormous, and much bigger than most can imagine. No tubes, no transistors, no phones, no computers, no Internet. Peter Cochrane holds the Collier Chair for the Public Understanding of Science & Technology at the University of Bristol. His home page is: |
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