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in Dundee. At College he became interested in physics and was appointed assistant to the Professor of Physics or, as it was then called, Natural Philosophy. He was encouraged by the Professor, William Peddle, to make a special study of wireless telegraphy

National Physical Laboratory

Following the outbreak of war he sought a job with the War Office in which he could use his knowledge of wireless; but there was nothing suitable and in 1915 he joined the Meteorological Office to work at Ditton Park (Slough) on radio methods of locating thunderstorms, the idea being that it might be possible to give warnings of such storms to pilots of aircraft. The difficulty of taking bearings on the brief atmospherics generated by thunderstorms led Watson-Watt to the use of rotating frame aerials and later, when cathode-ray tubes became available, to the cathode-ray direction finder.

There was another radio group at Ditton Park belonging to the National Physical Laboratory and in 1927, when the two groups were amalgamated to form the Radio Research Station, Watson-Watt was appointed Superintendent. As well as direction-finding the Station's work included measuring the height of the reflecting layers of the ionosphere by radio using pulses and a cathode-ray oscilloscope; it was Watson-Watt who coined the word 'ionosphere'2.

Committee for the Scientific Study of Air Defence

In early 1935 a Committee for the Scientific Study of Air Defence3 was set up by H. E. Wimperis (Director of Research at the Air Ministry) under the chairmanship of H. T. Tizard (later Sir Henry) (Fig. 2) to 'consider how far recent advances in scientific and technical knowledge can be used to strengthen the present methods of defence against hostile aircraft'. In retrospect those defences look absurd and as it turned out the review was made only just in time.

In an interesting article4 on the 'Prehistory of radar' Professor Burns reminds us that in the 1914-18 war, only about 20 years before the time we are considering, the only methods of detecting enemy aircraft were by eye and by ear. At night the eye was aided by searchlights and was remarkably unsuccessful: in 1915 there were 20 separate night raids by zeppelins, the defending aircraft made 81 sorties, sighted the enemy three times and failed to engage them at all (a zeppelin was about 180 m long and travelled at about 100 km h-1). Clearly there was an urgent need to strengthen the defences against hostile aircraft and a committee which included eminent scientists was appointed, much like the later Committee set up by Wimperis for the Scientific Study of Air Defence. In due course a scheme was put forward to help the eye by lighting up the sky at night, illuminating a belt 30 km wide and 160 km long. After some trials at Upavon in 1917 this scheme was abandoned4.

A good deal was also done to help the detection of aircraft by ear using sensitive microphones and sound reflectors. This work was continued actively after the 1914-18 war and by about 1930 a plan had been evolved for a coastal warning system for the south-eastern approaches to London using sound locators with 60 m and 10 m reflectors. The 60 m reflectors were able to detect an aircraft at a range of between 30 and 40 km, depending on the weather, and would therefore have given about 4 minutes warning of an aircraft approaching at 500 km h'. During the time which the sound took to travel to the reflector an aircraft would have moved about 15 km - not a promising basis for locating aircraft accurately! However, the construction of this system was halted in 1935 in view of the promising work on radar.

Before the first meeting of the new Committee for the Scientific Study of Air Defence, early in 1935, Wimperis asked Watson-Watt whether it would be possible to damage a hostile aircraft by radiation - in popular terms he asked him if it was possible to make a 'death-ray'? As the secretary of that Committee, A. P. Rowe, recalls5 in his book 'One story of radar' a death-ray was a hardy annual among optimistic inventors and the Air Ministry had, unsuccessfully, offered £1000 to anyone who could demonstrate a ray which would kill a sheep at a range of 100 yards.

Proposal of radar

In a memorandum3 to the Committee, Watson-Watt replied that to produce a death-ray for aircraft was not practicable, and he quoted some calculations which, I feel sure, were made by his assistant Arnold Wilkins. Representing a man by 75 kilogrammes of water with a cross-section of one square metre he estimated the


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Updated 18/12/00

Constructed by Dick Barrett

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©Copyright 2000 Dick Barrett

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