The War Years
radar | cavity wavemeters
| air raids | home
The head of the Division,
Watson Watt, had convinced the Air Ministry of the urgent need to develop radar
and a separate establishment had been set up for this purpose. Some of the less
secret parts of the problem, particularly those requiring precise measurement,
were left to the NPL.
Radar
One specific task
allocated to us was the design of an instrument for testing the electrical
properties of high 
frequency cables. It is interesting to
recall that polythene now so widely used for domestic appliances was originally
produced at government expense for these cables, its properties being almost
exactly right at wavelengths in the region of 10cm used for radar. But if the
cables did not meet a rigid specification much of the power was lost between
the oscillator and aerial or the aerial and receiver. One of our scientists was
already working on the project but since a rapid solution was needed it was
decided that it would be a good idea to have someone else approaching it in a
different way. One difference was that while my colleague was a sounder
electrical engineer I had something of a flair for getting apparatus to work.
In any case in this instance I soon had a piece of equipment which was
effective and easy to use. It was employed for testing samples of cable at the
NPL and was manufactured in sufficient numbers to supply all the cable firms
concerned. I had an interesting time installing them and formed a high opinion
of the way the firms co-operated.
It seemed to be
understood without anything being actually said that I should continue to be in
charge of frequency measurements, and with the help of an assistant who was an
electronics expert we kept abreast of the ever increasing range in the cm and
mm region (frequencies of 108 and 109 Hz). With the help
of special valves we multiplied the frequency of the standard so that we could
compare frequencies right through the range with that of the standard, indeed
keeping ahead of the world in this field. The equipment was too complicated and
bulky to use in the field and simpler devices known as cavity wavemeters were
developed.
Cavity wavemeters
The
electromagnetic theory formulated by Maxwell from the experimental work of
Faraday at the Royal Institution on the interaction of electric and magnetic
circuits, gave a precise description of the propagation of radio waves through
space, along wires and down metal pipes. This must be one of the greatest
achievements in science, although not sufficiently recognised. The scientific
establishment prefers to idolise Einstein, who as far as I can see contributed
little to the theory except some irrational ideas. In the cavity wavemeter
waves travel up and down a metal cylinder one end of which is attached to a
fine screw such as a micrometer head, enabling the length of the cylinder to be
altered. When it is equal to one or more half wave-lengths of the radiation,
resonance occurs just as an organ pipe resonates to a sound wave. The cylinder
is made from low resistance metal such as copper or silver plated steel and the
resonance is extremely sharp. The instrument is calibrated by reference to a
frequency meter and can then be used to give values of frequency immediately
with an accuracy of 0.01 per cent or better. The instruments were made
commercially in large numbers and calibrated at the NPL. For the first and only
time in my career there were quite a few people in my section. I designed what
I thought was a very neat form of wide range instrument and a number were made
in our workshop for other laboratories cheaply and without apparent difficulty
but a commercial firm which tried abandoned the attempt. It must be admitted
that the mechanic concerned was one of the best in our excellent shop. There
was no way of rewarding such skill and he left to go into greengrocery
business. A similar instrument was eventually made by a Swedish firm.
The theory
includes a constant “c” which as Maxwell predicted equals the velocity of
light. The resonant frequencies of cavity wavemeters can be calculated from
their dimensions and the known value of “c”, but it is much easier and more
accurate to calibrate them directly in terms of the frequency standard. It did
set me thinking about this constant and how accurately it was in fact known. My
war work was interesting and rewarding, bringing me into contact with some of
the brilliant scientists who had been enlisted from universities into service
departments as well as those remaining in universities on service contracts.
For example some of the special valves needed were made in a small workshop at
Oxford. The new techniques acquired opened up a whole new field of research for
me as soon as my immediate commitments were completed.
Air raids in Teddington
My domestic life
suffered the inconveniences common to us all. It was not easy for my wife to
cope with our two small children under the conditions of frequent air raids, no
household help, and strict rationing. She certainly showed great courage and
common sense in overcoming al our problems among which, of course, was my low
salary. Fortunately for us we only felt the full impact of a raid on one
occasion, and that no doubt by accident when a timber yard was struck and
served as a target. One bomb took off the spire of the local church before
landing on our skiff at Benn’s boat-house and several bombs landed in the
grounds of the NPL without causing serious damage. As an air raid warden I had
plenty of sleepless nights, although the close contact with the community was
rewarding. The inconveniences are long forgotten; a more lasting memory is the
friendliness of everyone and the spirit of comradeship throughout the country.
Class distinctions were set aside and nearly all of us were working together in
a common cause. The spirit continued for a time after the war and in spite of
the enormous task of reconstruction, liberal measures were introduced which did
more to improve the conditions of the ordinary people than any political action
before or since. Even on the international scene there were hopeful signs of a
better future with the formation of the United Nations and the high moral tone
of the speeches made by the world’s leaders, probably genuine at the time.
Gradually however there was a violent swing of the pendulum and I was
disheartened to see how greed and competition became more rampant than ever
endangering the future of mankind.
