Sir Edward Victor Appleton (6 September 1892 – 21 April 1965) was an English physicist who received the Nobel Prize in Physics in 1947 for his contributions to the knowledge of the ionosphere, which led to the development of radar and shortwave radio.
A graduate of the University of Cambridge, Appleton was commissioned as a second lieutenant for the Royal Engineers in 1915. During the First World War, he was an instructor at the Royal Engineers Signals Depot in Fenny Stratford, and served briefly on the Western Front. He brought a captured German thermionic valve back with him. He became the Wheatstone Professor of Physics at King's College London in 1924 and a fellow of the Royal Society in 1927. His primary research interests were how radio waves were created and propagated and unravelling the mystery of how they were reflected by the upper atmosphere.
Appleton returned to Cambridge in 1936 as Jacksonian Professor of Natural Philosophy and, when Ernest Rutherford died in October of that year, became acting director of the Cavendish Laboratory. In 1939, shortly before the outbreak of the Second World War, Appleton became the Secretary of the Department of Scientific and Industrial Research. In this role, he marshalled the scientific knowledge of Britain in service of the war effort. He was also closely involved with the development of radar, an outgrowth of his pre-war research into the ionosphere. He was also in charge of Tube Alloys, the British nuclear weapons project, which was merged into the American Manhattan Project in 1943.
From 1948 until his death in 1965, he was the Principal and Vice-Chancellor of the University of Edinburgh. As such, he oversaw its growth and was involved in the controversial redevelopment of the historic George Square.
Early life and education Edward Victor Appleton was born on 6 September 1892 in Bradford, England, the eldest child of Peter Appleton, a clerk who worked in a warehouse of Charles Senior & Co., and Mary Wilcock. He had two younger sisters, Isabel and Dorothy. He was named Edward after the tenor Edward Lloyd but preferred to use his middle name; to his family he was always "Vic". He attended Barkerend Primary School until, at the age of 11, he was awarded a scholarship to Hanson Boys' Grammar School, where he was captain of the school cricket and football teams. When he was 16, he won a City of Bradford scholarship to attend Bradford Grammar School but did not take it up.
Appleton sat and passed the London Matriculation Examination but then sat for and won the Isaac Holden scholarship in 1910. This was a three-year scholarship valued at that enabled him to enter the University of Cambridge, although he had to wait another year because the university would not admit him until he turned 19. In 1911, he was awarded an exhibition at St John's College, Cambridge, where he obtained a B.A. in Natural Science in 1913, and an M.A. in Physics in 1914. The same year, he received the Hutchinson Research Studentship, which enabled him to study under J. J. Thomson and Ernest Rutherford. At Cambridge, he met Sir Oliver Lodge and Guglielmo Marconi, and during the long vacation, he assisted Lawrence Bragg in his work on X-ray crystallography of metals in the Cavendish Laboratory.
Great War While at Cambridge, Appleton had served in the University Officers' Training Corps. On the outbreak of the First World War in August 1914, Appleton applied for a commission in the Royal Engineers. By September, he had tired of waiting for this and enlisted as a private in the 16th Battalion, West Yorkshire Regiment, also known as the "1st Bradford Pals Battalion". He was soon promoted to corporal. His application for a commission eventually came through, and he was commissioned as a second lieutenant in the Royal Engineers on 9 January 1915. After engineer training at Aldershot, he was sent to Malvern, Worcestershire, for the first general radio course for officers, which was taught by Captain C. F. Trippe, who later played an important role in the industrial development of the thermionic valve. Appleton topped the class on the course examination and was asked to conduct the second course when Trippe fell ill. He was then posted to the Royal Engineers Signals Depot in Fenny Stratford, where he was stationed for the rest of the war.
On 29 May 1915, Appleton married his distant cousin Jessie Longson, the daughter of Reverend John Longson, a Baptist minister. Jessie worked for Lister Mills as a textile designer, creating patterns in silk. After the war they had two daughters: Margery, born in 1920, and Rosalind, born in 1927. Appleton was promoted to the temporary rank of lieutenant on 23 August 1916, and captain on 1 January 1918. Married subalterns were uncommon in those days, and Appleton and Jessie shared a cottage in Fenny Stratford with another lieutenant and his wife.
In 1915, the British Army in France found that its ration parties were being engaged by German artillery, who apparently had intelligence of their activities. The mystery began to unravel after the French captured a German device that was handed over to the British. Appleton and Captains Algernon Fuller and Edward Stevens examined the device and found it consisted of a two-valve amplifier with two pairs of phones and several pairs of terminals. When the terminals were earthed the device could listen in on Army field telephone traffic. The obvious countermeasure was to use twisted pair cabling but this was expensive. After discussion among the three men, Fuller came up with the fullerphone, a device that worked with the existing telephone lines but was far more difficult to tap. In December 1917, Appleton went to the Western Front for a fortnight to demonstrate the use of radios, and he tested the fullerphone in the field, and found that it worked with as little as a micro-ampere of current. He brought a captured German thermionic valve back with him. He was fascinated with the properties of the valve, which he would research on returning to Cambridge. After the war ended, Appleton relinquished his commission on 17 January 1919.
Between the wars Appleton returned to Cambridge, where he was elected a fellow of St John's College. At first, he was a research student at the Cavendish Laboratory under Thomson, who was succeeded that year by Rutherford. In 1920, Appleton joined the staff of the Cavendish Laboratory as an assistant demonstrator in physics. He was initiated into Freemasonry in 1922. Under Rutherford, the Cavendish Laboratory was drawn deeper into nuclear physics research, but Appleton's interest was exploring radio: the way that radio waves were created by thermionic valves, how they propagated, and the mysterious fluctuations in their reception.
In his investigation of the properties of the thermionic valve, Appleton collaborated with Balthasar van der Pol, a Dutch scientist who had been a fellow research student at the Cavendish Laboratory before the war. Van der Pol considered returning to Cambridge, but Appleton warned him that lectureships paid no more than per year. Appleton would be reduced to when his fellowship expired. Van der Pol therefore decided to join Philips instead. Together, they wrote a textbook on the subject, Thermionic Vacuum Tubes, which was published in 1932.
Ionosphere In his atmospheric research, Appleton worked with the Radio Research Board, of which he became a member in 1926 and served on until 1939. The Radio Research Board provided him with grants to continue his work and its Radio Research Station at Ditton Park, near Slough, collaborated with the Cavendish Laboratory in its atmospheric research. He also established a field station near Peterborough where his Cavendish Laboratory research student Miles Barnett conducted experiments under his direction. This station moved to Hampstead in 1932. In October 1924, Appleton was appointed Wheatstone Professor of Physics at King's College London. He became a fellow of the Royal Society in 1927.
Appleton had observed that the strength of medium wave radio signals was constant during the day but variable at night. He theorised that this was due to a signal bouncing off the upper atmosphere. This would result in two signals being received, which would interfere with each other. The resulting wave interference pattern would account for the variable strength of the signal. The existence of a reflecting atmospheric layer was not in itself a completely new idea; Balfour Stewart had suggested the idea in the late 19th century to explain rhythmic changes in the Earth's magnetic field. More recently, in 1902, Oliver Heaviside and Arthur E. Kennelly had suggested such an electromagnetic-reflecting stratum—now called the Kennelly–Heaviside layer—that may explain the success Marconi had in transmitting his signals across the Atlantic. Calculations had shown that natural bending of the radio waves was not sufficient to stop them from simply "shooting off" into space before they reached the receiver. Appleton thought the best place to look for evidence of the ionosphere was in the variation in the range of radio signal reception that occurred each night around sunset. It was sensible to suggest these variations were due to the interference of two waves but an extra step to show that the second wave causing the interference (the first being the ground wave) was coming down from the ionosphere. The experiment he designed had two methods to show ionospheric influence and both allowed the height of the lower boundary of reflection (thus the lower boundary of the reflecting layer) to be determined. The first method was called frequency modulation (FM) and the second was to calculate the angle of arrival of the reflected signal at the receiving aerial. The FM method exploits the fact that there is a path difference between the ground wave and the reflected wave, meaning they travel different distances from sender to receiver. Let the distance AC travelled by the ground wave be h and the distance ABC travelled by the reflected wave h' . The path difference is:
The wavelength of the transmitted signal is λ. The number of wavelengths difference between the paths h and h' is:
If N is an integer number, then constructive interference will occur, this means a maximum signal will be achieved at the receiving end. If N is an odd integer number of half-wavelengths, then destructive interference will occur and a minimum signal will be received. Let us assume we are receiving a maximum signal for a given wavelength λ. If we start to change λ, this is the process called frequency modulation, N will no longer be a whole number and destructive interference will start to occur, meaning the signal will start to fade. Now we keep changing λ until a maximum signal is once again received. This means that for our new value λ', our new value N' is also an integer number. If we have lengthened λ then we know that N' is one less than N. Thus:
Rearranging for D gives:
As we know λ and λ', we can calculate D. Using the approximation that ABC is an isosceles triangle, we can use our value of D to calculate the height of the reflecting layer. This method is a slightly simplified version of the method used by Appleton and his student, Miles Barnett, to work out a first value for the height of the ionosphere in 1924. In their experiment, they used the BBC broadcasting station in Bournemouth to vary the wavelengths of its emissions after the evening programmes had finished. They installed a receiving station in Oxford to monitor the interference effects. The receiving station had to be in Oxford as there was no suitable emitter at the right distance of about from Cambridge in those days.