Sir Edward Victor Appleton

A summary of the history and life of Sir Edward Appleton, the man who proved the ionosphere existed and enabled an understanding of world-wide radio signal propagation.

Sir Edward Victor Appleton was one of the key figures of the twentieth century who contributed to the knowledge of radio and the ionosphere and hence improved our knowledge of the way in which radio waves propagate in the HF portion of the spectrum.

Edward Appleton received a Nobel prize in 1947 for his work, the technique for which laid the foundations for the development of radar. He became Sir Edward Appleton when he was knighted in 1941.

Early years

The history of Edward Victor Appleton starts with his birth on 6th September 1892 in Bradford England. The city is in Yorkshire and was famous for its wool mills and was a centre of industry. Edward Appleton was the son of Peter and Mary Appleton.

The young Appleton received his early education at Hanson Grammar School in Bradford. Initially he showed little interest in anything apart from music and cricket, although at the age of 18 he won a scholarship to St John's College, Cambridge University where he studied under famous names including Sir J J Thomson and Lord Rutherford. Appleton was very successful and not only did he win prizes for his work and ultimately gained a first class degree in Natural Sciences.

Outbreak of War

With the outbreak of the First World War, Edward Appleton joined the armed forces, initially with West Riding Regiment, but later transferring to the Royal Engineers. While in the army, he trained on the relatively new technology of radio or as it was called then "wireless". This obviously interested him considerably because after the cessation of hostilities he returned to Cambridge in 1920 and took up research on radio waves. Here Appleton started as an assistant demonstrator of physics under J J Thomson. He soon developed an interest in wireless or radio valves, as well as in the propagation of wireless or radio signals.

Research begins

In 1924 Edward Appleton was appointed Professor of Physics at King's College of London University. He held this post for 12 years and it was during this time that he undertook much of his work on what was termed the Kennelly-Heaviside layer. This was a layer in the upper atmosphere that reflected radio signals, enabling the radio signals to be heard over great distances. This work was to lay not only the foundations for much of our knowledge of the ionosphere, but also for the later development of radar.

Much of the work Appleton undertook at Kings was based at their campus on the Strand in London. However his experiments caused interference to many others in the locality, and eventually his work was transferred to another Campus opened by the college in Hampstead in the outer suburbs of London. There was more space in this area and fewer radio users. Accordingly the interference to others was kept within acceptable limits.

The idea of a layer in the upper reaches of the atmosphere that could reflect radio signals had been postulated for some years. In 1901 Marconi made the first transatlantic radio transmission and this made it obvious that there must have been some mechanism to "bend" the radio signals. Then in 1902 Oliver Heaviside and A.E.Kennelly independently postulated the idea of the presence of a conducting layer. This was termed the Kennelly-Heaviside Layer.

Additionally Appleton had observed that the strength of the radio signal from a transmitter a on a frequency such as the medium wave band and over a path of a hundred miles or so was constant during the day but varied during the night, rising and falling in a regular manner. This lead to him to believe that it was possible that two radio signals were being received, one traveling along the ground, and another reflected by a layer in the upper atmosphere. The fading or variation in strength of the overall radio signal received resulted from the interference pattern of the two signals. The variation, he postulated, was caused by small changes in the reflecting medium causing the path length to change and hence the way in which the two radio signals interfered. Sometimes this would be constructive interference when the two radio signals would add together, and at other times it would be destructive when the two signals would tend to cancel each other out.

Appleton used the British Broadcasting Corporation (BBC) radio broadcast transmitter at Bournemouth England and transmitted a signal towards the upper layers in the atmosphere. He received the radio signals near Cambridge, proving they were being reflected. By making a periodic change to the frequency of the broadcast radio signal he was able to measure the time taken for the signals to travel to the layers in the upper atmosphere and back. In this way he was able to calculate that the height of the reflecting layer was 60 miles above the ground. The technique he used is now known as frequency modulation radar, and the layer in the ionosphere was the first item to be located using a radar technique.

Appleton realized that the reflections in this experiment could have conceivably been caused by reflections from distant hills or other objects, although if this were so it would not explain the fading of the radio signals that was observed. To ensure that this was not the case, he repeated the experiments some months later but used a directional radio antenna, thereby proving that the reflected signal was indeed emanating from the upper reaches of the atmosphere. In this way he eliminated any doubt about the mechanism of the way in which the radio signals propagated.

Further researches

Appleton continued his work on the ionosphere and in 1926 discovered a further layer above the lower Kennelly-Heaviside layer. This one at an altitude of between 250 and 350 kilometres was named the Appleton layer.

Later Appleton refined his method of measuring the height and nature of the ionosphere using a transmitter that sent out pulses of energy. The results of the reflected signals could then be displayed on an oscilloscope, giving a visual image.

Appleton found that the more he was discovering about what was now termed the ionosphere was posing more questions. For example it had been noticed that the ionosphere varied over time, but it was not understood what caused the changes. Accordingly Appleton continued his researches. A solar eclipse on 29th June 1927 provided a unique opportunity to investigate the effect of the Sun on the ionosphere. He discovered that as soon as the Sun was hidden by the Moon, the effective height of the Appleton layer increased. This suggested that the Sun had a direct effect on the layer and that radiation from the Sun was required to ionise the upper atmosphere. From this and other researches, the Appleton-Hartreee equation was developed. This showed that the charges that caused the "reflection" were free negatively charged electrons.

There were other discoveries Appleton made. He found that the height of the ionospheric layers was affected by the Moon as well as the Sun, and that they were strongly influenced by the earth's magnetic field and linked to this Appleton discovered that the polar blackouts were caused by magnetic storms.

Career

Edward Appleton was clearly a very gifted research scientist. After undertaking much of his research at the University of London between the years of 1924 and 1936. During this period he was elected Vice President of the American Institute of Radio Engineers. After his time at London University he took up the post of Professor of Natural Philosophy at Cambridge University between 1936 and 1939. After hostilities broke out in 1939, Appleton was appointed as the secretary of the Dept. of Scientific and Industrial Research. In this position he had considerable responsibility in defining the scientific research that was undertaken within Britain.

War years

One of the main achievements of the early war years was radar which was used for the early detection of aircraft. This was based on the original scheme used by Appleton for the detection of the ionospheric layers. The development of the radar system was undertaken by Robert (later Sir Robert) Watson-Watt. He stated that had it not been for the work undertaken by Appleton, then radar would have been developed too late for use in the Battle of Britain.

As a result of his work, Appleton was knighted in 1941. He also became a member of the Scientific Advisor Committee of the War Cabinet. In this capacity he was one of the committee that advised the War Cabinet on the feasibility of creating an Atomic Bomb.

Despite the heavy work load associated with his position in the Scientific Advisor Committee and with his involvement in the development of the Atomic Bomb, Appleton still found some time to continue with his researches into radio signal propagation and the ionosphere. He also discovered that the condition of the ionosphere was heavily dependent upon the number of sunspots on the sun, and when working with Dr. J S Hey he discovered that these sunspots were powerful emitters of radio signals.

Awards

In view of the tremendous contributions Edward Appleton had made to the advancement of radio and science in general he was given many awards. He was awarded the Nobel Prize for Physics in 1947. He was also awarded the Medal of Merit, the highest civilian award given by the United States. France made him an Officer of the French Legion of Honour, and Norway, the Norwegian Cross of Freedom, and in 1948 the Pope appointed him to the Pontifical Academy of Science.

These are but a few of the awards given to Sir Edward Appleton. However in 1949 he moved to the University of Edinburgh to become Principal and Vice-Chancellor, a position that he held for the rest of his life. However Appleton died on 21st April 1965

Edward Appleton facts

A summary of some of the chief facts about Edward Appleton:

Key Edward Appleton Facts
Fact	Details
Birth date	6 September 1892
Birth place	Bradford, Yorkshire, England
Parents	Peter and Mary Appleton
Death	21 April 1965
Education	Hanson Grammar School Bradford, then Cambridge University
Academic position held	Professor of Physics at King's College of London in 1924
Major work	Studies of ionosphere and discovery of the Appleton layer
Also known for	Work on radar