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.Their joint research was financed by grants from the Paul Fund and the Royal Society.The Professor hoped to develop sonar as a means of precise geological surveying.Sonar, as you will know, is the acoustic equivalent of radar, and although less familiar is older by some millions of years, since bats use it very effectively to detect insects and obstacles at night.Professor Hancock intended to send high-powered supersonic pulses into the ground and to build up from the returning echoes an image of what lay beneath.The picture would be displayed on a cathode ray tube and the whole system would be exactly analogous to the type of radar used in aircraft to show the ground through cloud.In 1957 the two scientists had achieved a partial success but had exhausted their funds.Early in 1958 they applied directly to the government for a block grant.Dr Clayton pointed out the immense value of a device which would enable us to take a kind of X-ray photo of the Earth’s crust, and the Minister of Fuel gave it his approval before passing on the application to us.At that time the report of the Bernal Committee had just been published and we were very anxious that deserving cases should be dealt with quickly to avoid further criticisms.I went to see the Professor at once and submitted a favourable report; the first payment of our grant (S/543A/68) was made a few days later.From that time I have been continually in touch with the research and have assisted to some extent with technical advice.The equipment used in the experiments is complex, but its principles are simple.Very short but extremely powerful pulses of supersonic waves are generated by a special transmitter which revolves continuously in a pool of a heavy organic liquid.The beam produced passes into the ground and ‘scans’ like a radar beam searching for echoes.By a very ingenious time-delay circuit which I will resist the temptation to describe, echoes from any depth can be selected and so pictures of the strata under investigation can be built up on a cathode ray screen in the normal way.When I first met Professor Hancock his apparatus was rather primitive, but he was able to show me the distribution of rock down to a depth of several hundred feet and we could see quite clearly a part of the Bakerloo Line which passed very near his laboratory.Much of the Professor’s success was due to the great intensity of his supersonic bursts; almost from the beginning he was able to generate peak powers of several hundred kilowatts, nearly all of which was radiated into the ground.It was unsafe to remain near the transmitter, and I noticed that the soil became quite warm around it.I was rather surprised to see large numbers of birds in the vicinity, but soon discovered that they were attracted by the hundreds of dead worms lying on the ground.At the time of Dr Clayton’s death in 1960, the equipment was working at a power level of over a megawatt and quite good pictures of strata a mile down could be obtained.Dr Clayton had correlated the results with known geographical surveys, and had proved beyond doubt the value of the information obtained.Dr Clayton’s death in a motor accident was a great tragedy.He had always exerted a stabilising influence on the Professor, who had never been much interested in the practical applications of his work.Soon afterward I noticed a distinct change in the Professor’s outlook, and a few months later he confided his new ambitions to me.I had been trying to persuade him to publish his results (he had already spent over £50,000 and the Public Accounts Committee was being difficult again), but he asked for a little more time.I think I can best explain his attitude by his own words, which I remember very vividly, for they were expressed with peculiar emphasis.‘Have you ever wondered,’ he said, ‘what the Earth really is like inside? We’ve only scratched the surface with our mines and wells.What lies beneath is as unknown as the other side of the Moon.‘We know that the Earth is unnaturally dense—far denser than the rocks and soil of its crust would indicate.The core may be solid metal, but until now there’s been no way of telling.Even ten miles down the pressure must be thirty tons or more to the square inch and the temperature several hundred degrees.What it’s like at the centre staggers the imagination: the pressure must be thousands of tons to the square inch.It’s strange to think that in two or three years we may have reached the Moon, but when we’ve got to the stars we’ll still be no nearer that inferno four thousand miles beneath our feet.‘I can now get recognisable echoes from two miles down, but I hope to step up the transmitter to ten megawatts in a few months
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