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<br><br>It is very common to have a dental emergency -- a fractured tooth, an abscess, or severe pain when chewing. Over-the-counter pain medication is just masking the problem. Seeing an emergency dentist is critical to getting the source of the problem diagnosed and corrected as soon as possible.<br><br>Here are some common dental emergencies:<br>Toothache: The most common dental emergency. This generally means a badly decayed tooth. As the pain affects the tooth's nerve, treatment involves gently removing any debris lodged in the cavity being careful not to poke deep as this will cause severe pain if the nerve is touched. Next rinse vigorously with warm water. Then soak a small piece of cotton in oil of cloves and insert it in the cavity. This will give temporary relief until a dentist can be reached.<br><br>At times the pain may have a more obscure location such as decay under an old filling. As this can be only corrected by a dentist there are two things you can do to help the pain. Administer a pain pill (aspirin or some other analgesic) internally or dissolve a tablet in a half glass (4 oz) of warm water holding it in the mouth for several minutes before spitting it out. DO NOT PLACE A WHOLE TABLET OR ANY PART OF IT IN THE TOOTH OR AGAINST THE SOFT GUM TISSUE AS IT WILL RESULT IN A NASTY BURN.<br><br>Swollen Jaw: This may be caused by several conditions the most probable being an abscessed tooth. In any case the treatment should be to reduce pain and swelling. An ice pack held on the outside of the jaw, (ten minutes on and ten minutes off) will take care of both. If this does not control the pain, an analgesic tablet can be given every four hours.<br><br>Other Oral Injuries: Broken teeth, cut lips, bitten tongue or lips if severe means a trip to a dentist as soon as possible. In the mean time rinse the mouth with warm water and place cold compression the face opposite the injury. If there is a lot of bleeding, apply direct pressure to the bleeding area. If bleeding does not stop get patient to the emergency room of a hospital as stitches may be necessary.<br><br>Prolonged Bleeding Following Extraction: Place a gauze pad or better still a moistened tea bag over the socket and have the patient bite down gently on it for 30 to 45 minutes. The tannic acid in the tea seeps into the tissues and often helps stop the bleeding. If bleeding continues after two hours, call the dentist or take patient to the emergency room of the nearest hospital.<br><br>Broken Jaw: If you suspect the patient's jaw is broken, bring the upper and lower teeth together. Put a necktie, handkerchief or towel under the chin, tying it over the head to immobilize the jaw until you can get the patient to a dentist or the emergency room of a hospital.<br><br>Painful Erupting Tooth: In young children teething pain can come from a loose baby tooth or from an erupting permanent tooth. Some relief can be given by crushing a little ice and wrapping it in gauze or a clean piece of cloth and putting it directly on the tooth or gum tissue where it hurts. The numbing effect of the cold, along with an appropriate dose of aspirin, usually provides temporary relief.<br><br>In young adults, an erupting 3rd molar (Wisdom tooth), especially if it is impacted, can cause the jaw to swell and be quite painful. Often the gum around the tooth will show signs of infection. Temporary relief can be had by giving aspirin or some other painkiller and by dissolving an aspirin in half a glass of warm water and holding this solution in the mouth over the sore gum. AGAIN DO NOT PLACE A TABLET DIRECTLY OVER THE GUM OR CHEEK OR USE THE ASPIRIN SOLUTION ANY STRONGER THAN RECOMMENDED TO PREVENT BURNING THE TISSUE. The swelling of the jaw can be reduced by using an ice pack on the outside of the face at intervals of ten minutes on and ten minutes off.<br><br>If you adored this article and also you desire to be given details about [http://www.youtube.com/watch?v=90z1mmiwNS8 Best Dentists in DC] kindly visit our page.
{{Use British English|date=August 2013}}
{{Use dmy dates|date=August 2013}}
{{Infobox scientist
| name              = Sir Edward Appleton
| image            = Appleton.jpg
| image_size        = 190px
| caption          =
| birth_name        = Edward Victor Appleton
| birth_date        = {{Birth date|1892|9|6|df=y}}
| birth_place      = [[Bradford]], [[West Yorkshire]], [[England]]
| death_date        = {{Death date and age|1965|4|21|1892|9|6|df=y}}
| death_place      = [[Edinburgh]], [[Scotland]]
| nationality      = [[England|English]]
| field            = [[Physics]]
| workplaces        = [[University of Cambridge]]<br />[[King's College London]]<br />[[University of Edinburgh]]<br>[[Cavendish Laboratory]]
| alma_mater        = [[St John's College, Cambridge]]
| doctoral_advisor  = <!--The PhD had only just started in Cambridge in 1919-->
| academic_advisors = [[J. J. Thomson]] <br />[[Ernest Rutherford]]
| doctoral_students =
| notable_students  = [[J. A. Ratcliffe]]<br />[[Charles Oatley]]
| known_for        = [[Ionosphere|Ionospheric Physics]]<ref>{{cite doi|10.1038/157691a0}}</ref><ref>{{cite doi|10.1038/115333a0}}</ref><ref>{{cite doi|10.1126/science.106.2740.17}}</ref><ref>{{cite doi|10.1038/136548b0}}</ref><ref name="ion">{{Cite journal|author=Appleton, EV|year=1932|title=Wireless Studies of the Ionosphere|journal=J. Inst. Elec. Engrs.|doi=10.1049/jiee-1.1932.0144}}</ref><ref>{{Cite doi|10.1098/rspa.1927.0093}}</ref><ref>{{Cite doi|10.1098/rspa.1925.0149}}</ref><br />[[F region|Appleton layer]]<Br>Demonstrating existence of [[Kennelly–Heaviside layer]]
| prizes            = {{nowrap|[[Nobel Prize in Physics]] (1947)}}<br>[[Fellow of the Royal Society]] (1927)<ref name="frs">{{cite doi|10.1098/rsbm.1966.0001}}</ref><br>[[Faraday Medal]]<br>[[Hughes Medal]]<br>[[Royal Medal]]<br>[[Appleton Medal and Prize|Chree Medal]]
}}
 
'''Sir Edward Victor Appleton''', [[Order of the British Empire|GBE]], [[Knight Commander of the Order of the Bath|KCB]], [[Fellow of the Royal Society|FRS]]<ref name="frs"/> (6 September 1892 – 21 April 1965)  was an [[United Kingdom|English]] [[physicist]].<ref>{{cite web|title=Sir Edward Appleton (1892–1965)|url=http://www.bbc.co.uk/history/historic_figures/appleton_edward.shtml}}</ref><ref>{{cite doi|10.1063/1.3047706}}</ref><ref>{{cite encyclopedia | last=Süsskind | first=Charles | title=Appleton, Edward Victor | encyclopedia=[[Dictionary of Scientific Biography]] | volume=1 | pages=195–196  | publisher=Charles Scribner's Sons | location=New York | year=1970 | isbn=0-684-10114-9}}</ref><ref>{{Cite doi|10.1098/rsta.1975.0088}}</ref><ref name="odnb">{{cite doi|10.1093/ref:odnb/30426 }}</ref><ref>{{cite doi|10.1126/science.119.3082.103}}</ref><ref name="pergamon">{{Cite book|last=Clark|first=Ronald|year=1971|title=Sir Edward Appleton|publisher=Pergamon Press |location=Oxford}}</ref>
 
==Biography==
Appleton was born in [[Bradford]], [[West Yorkshire]], and educated at [[Hanson School|Hanson Grammar School]]. At the age of 18 he won a scholarship to [[St John's College, Cambridge]]. He graduated with a first class degree in Natural Sciences.
 
During the First World War he joined the [[Duke of Wellington's Regiment|West Riding Regiment]], and later transferred to the [[Royal Engineers]]. After returning from active service in [[World War I]], Appleton became assistant demonstrator in experimental physics at the [[Cavendish Laboratory]] in 1920. He was professor of physics at [[King's College London]] (1924–36) and professor of natural philosophy at the [[University of Cambridge]] (1936–39). From 1939 to 1949 he was secretary of the [[Department of Scientific and Industrial Research]]. Knighted in 1941, he received the 1947 [[Nobel Prize in Physics]] for his contributions to the knowledge of the [[ionosphere]],<ref name="ion"/> which led to the development of [[radar]].
 
From 1949 until his death in 1965, he was Principal and Vice-Chancellor of the [[University of Edinburgh]].<ref>{{cite book | first=Derek A J| last=Lister | title=Bradford's Own | year=2004 | publisher=Sutton | isbn=0-7509-3826-9}}</ref> In 1956, the BBC invited him to deliver the annual [[Reith Lectures]]. Across a series of six radio broadcasts, titled ''Science and the Nation'', Appleton explored the many facets of scientific activity in Britain at the time.
 
== Works ==
Appleton had observed that the strength of the radio signal from a transmitter 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 that it varied during the night. This led him to believe that it was possible that two radio signals were being received. One was travelling along the ground, and another was reflected by a layer in the upper atmosphere. The fading or variation in strength of the overall radio signal received resulted from the [[Interference (wave propagation)|interference]] pattern of the two signals.
 
The existence of a reflecting atmospheric layer was not in itself a completely new idea.  Balfour Stewart had suggested the idea in the late nineteenth century to explain rhythmic changes in the earth’s magnetic field. More recently, in 1902, [[Oliver Heaviside]] and A. E. Kennelly had suggested such a hypothesis 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 empty space before they reached the receiver.
 
Appleton thought the best place to look for evidence of the ionosphere was in the variations he believed it was causing around sunset in radio signal receptions.  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 and the second was to calculate the angle of arrival of the reflected signal at the receiving aerial.
 
The frequency modulation 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:
 
<math> h'-h=D  </math>
 
The wavelength of the transmitted signal is λ .  The number of wavelengths difference between the paths h and h’ is:
 
<math> \frac{h-h'}{\lambda}=\frac{D}{\lambda}=N  </math>
 
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.  The means that for our new value  λ’, our new value N’ is an also an integer number.  If we have lengthened λ then we know that N’ is one less than N. Thus:
 
<math> N-N'=\frac{D}{\lambda}-\frac{D}{\lambda'}=1  </math>
 
Rearranging for D gives:
 
<math> D=h-h'=\frac{1}{\frac{1}{\lambda}-\frac{1}{\lambda'}}  </math>
 
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 colleagues 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 100&nbsp;km from Cambridge in those days.
 
This frequency modulation method revealed that the point from which waves were being reflected was approximately 90&nbsp;km.  However, it did not establish that the waves were reflected from above, indeed they may have been coming from hills somewhere between Oxford and Bournemouth.  The second method, which involved finding the angle of incidence of the reflected waves at the receiver, showed for sure that they were coming from above.  Triangulations from this angle gave results for the height of reflection compatible with the frequency modulation method. We will not go into this method in detail because it involves fairly complex calculations using Maxwell’s electromagnetic theory.
 
Far from being conclusive, the success of the Oxford-Bournemouth experiment revealed a vast new field of study to be explored. It showed that there was indeed a reflecting layer high above the earth but it also posed many new questions.  What was the constitution of this layer, how did it reflect the waves, was it the same all over the earth, why did its effects change so dramatically between day and night, did it change throughout the year?  Appleton would spend the rest of his life answering these questions.  He developed a magneto-ionic theory based on the previous work of [[Hendrik Lorentz|Lorentz]] and [[James Clerk Maxwell|Maxwell]] to model the workings of this part of the atmosphere.  Using this theory and further experiments, he showed that the so-called [[Kennelly-Heaviside layer]] was heavily ionised and thus conducting.  This led to the term ionosphere. He showed free electrons to be the ionising agents.  He discovered that the layer could be penetrated by waves above a certain frequency and that this critical frequency could be used to calculate the electron density in the layer. However these penetrating waves would also be reflected back, but from a much higher layer.  This showed the ionosphere had a much more complex structure than first anticipated.  The lower level was labelled E – Layer, reflected longer wavelengths and was found to be at approximately 125&nbsp;km.  The high level, which had much higher electron density, was labelled F – Layer and could reflect much shorter wavelengths that penetrated the lower layer.  It is situated 300 – 400&nbsp;km above the earth’s surface.  It is this which is often referred to as the Appleton Layer as is responsible for enabling most long range short wave telecommunication.<ref>{{cite web |url=http://www.ieeeghn.org/wiki/index.php/Edward_V._Appleton |title=Edward V. Appleton |author=IEEE Global History Network |year=2011 |publisher=IEEE History Center |accessdate=14 July 2011}}</ref>
 
The magneto-ionic theory also allowed Appleton to explain the origin of the mysterious fadings heard on the radio around sunset.  During the day, the light from the sun causes the molecules in the air to become ionised even at fairly low altitudes.  At these low altitudes, the density of the air is great and thus the electron density of ionised air is very large.  Due to this heavy ionisation, there is strong absorption of electromagnetic waves caused by ‘electron friction’. Thus in transmissions over any distance, there will be no reflections as any waves apart from the one at ground level will be absorbed rather than reflected. However, when the sun sets, the molecules slowly start to recombine with their electrons and the free electron density levels drop.  This means absorption rates diminish and waves can be reflected with sufficient strengths to be noticed, leading to the interference phenomena we have mentioned.  For these interference patterns to occur though, there must not simply be the presence of a reflected wave but a change in the reflected wave.  Otherwise the interference is constant and fadings would not be heard.  The received signal would simply be louder or softer than during the day.  This suggests the height at which reflection happens must slowly change as the sun sets.  Appleton found in fact that it increased as the sun set and then decreased as the sun rose until the reflected wave was too weak to record.  This variation is compatible with the theory that ionisation is due to the sun’s influence.  At sunset, the intensity of the sun’s radiation will be much less at the surface of the earth than it is high up in the atmosphere. This means ionic recombination will progress slowly from lower altitudes to higher ones and therefore the height at which waves are reflected slowly increases as the sun sets.
 
The basic idea behind Appleton’s work is so simple that it is hard to understand at first how he devoted almost all of his scientific career to its study.  However, in the last couple of paragraphs some of the complexities of the subject have been introduced.  Like many other fields, it is one that grows in intricacy the more it is studied.    By the end of his life, ionospheric observatories had been set up all over the world to provide a global map of the reflecting layers.  Links were found to the 11 year sunspot cycle and the [[Aurora Borealis]], the magnetic storms that occur in high latitudes.  This  became particularly relevant during the second world war when the storms would lead to radio blackouts. Thanks to Appleton’s research, the periods when these would occur could be predicted and communication could be switched to wavelengths that would be least affected.  [[RADAR]], another crucial wartime innovation, was one that came about thanks to Appleton’s work.  On a very general level, his research consisted in determining the distance of reflecting objects from radio signal transmitters.  This is exactly the idea of RADAR and the flashing dots that appear on the screen (a cathode ray tube) scanned by the circulating ‘searcher’ bar.  This system was developed partly by Appleton as a new method, called the pulse method, to make ionospheric measurements.    It was later adapted by [[Robert Watson-Watt]] to detect aeroplanes.  Nowadays, ionospheric data is important when communications with satellites are considered.  The correct frequencies for these signals must be selected so that they actually reach the satellites without being reflected or deviated before.
 
In 1974 the [[Radio Research Station|Radio and Space Research Station]] was renamed the [[Appleton Laboratory]] in honour of the man who had done so much to establish the UK as a leading force in ionospheric research, and had been involved with the station first as a researcher and then as secretary of its parent body, the Department of Scientific and Industrial Research.
 
== Honours and awards ==
Appleton was awarded the following:
* Fellow of the [[Royal Society]] (1927)<ref name="frs"/>
* Foreign Honorary Member of the [[American Academy of Arts and Sciences]] (1936)<ref name=AAAS>{{cite web|title=Book of Members, 1780–2010: Chapter A|url=http://www.amacad.org/publications/BookofMembers/ChapterA.pdf|publisher=American Academy of Arts and Sciences|accessdate=19 April 2011}}</ref>
* [[Nobel Prize in Physics]] (1947)
* [[Faraday Medal]]
* [[Hughes Medal]]
* [[Royal Medal]]
* [[Appleton Medal and Prize|Chree Medal]]
In addition the following are named in his honour:
* the [[Rutherford Appleton Laboratory]]
* the [[Appleton Medal and Prize]]
* the Appleton Suite at Bradford Registry Offices
* the [[Appleton Tower]] at the [[University of Edinburgh]]
* the [http://www.bilk.ac.uk/college/depts/science/ Appleton Science Building] at [[Bradford College (England)|Bradford College]]
* Appleton Academy, a new school, which will replace Wyke Manor School and High Fernley Primary School in the Wyke district of [[Bradford|South Bradford]]. This will be the first 'through-school' in West Yorkshire.
* The crater [[Appleton (crater)|Appleton]] on the [[Moon]] is named in his honour.
* The Appleton Layer, which is the higher atmospheric ionized layer above the E-layer
* The annual [http://www.theiet.org/events/appleton/ Appleton Lecture] at the [[Institution of Engineering and Technology]]
* Likely inspiration for the pseudonym [[Victor Appleton]] – the fictitious author of the [[Tom Swift]] series of novels{{or|date=September 2013}}
 
== References ==
{{Reflist}}
 
==Further reading==
* {{Cite book|last=Appleton |first=EV |author2=Ratcliffe, JA|year=1929|title=The Physical Principles of Wireless|publisher=Methuen }}
* [http://conferences.theiet.org/lectures/appleton/index.htm IET Appleton lectures]
* [http://nobelprize.org/physics/laureates/1947/index.html "Sir Edward Victor Appleton"].  ''nobelprize.org''. Accessed 21 October 2007. (Citation: Nobel Prize in Physics: 1947, "for his investigations of the physics of the upper atmosphere especially for the discovery of the so-called Appleton layer."  [Hyperlinked account.  Provides link to BBC ''Historic Figures'' biography.]
* [http://nobelprize.org/nobel_prizes/physics/laureates/1947/appleton-bio.html "Sir Edward Victor Appleton: Nobel Prize in Physics 1947"] – Biography from ''Nobel Lectures, Physics 1942–1962'' (Amsterdam: Elsevier Publishing Company, 1964).  [Hyperlinked in previous entry.]
* [http://www.bbc.co.uk/history/historic_figures/appleton_edward.shtml "Sir Edward Victor Appleton (1892–1965):] Appleton was an English physicist and Nobel prize winner who discovered the ionosphere."  ''Historic Figures'', ''bbc.co.uk''.  Accessed 21 October 2007.  (Photograph of Appleton c. 1935 ©). [Provides link to Nobel Foundation account, listed above.]
* [http://nobelprize.org/nobel_prizes/physics/laureates/1947/appleton-bio.html Nobelprize.org Biography]
* ''[http://www.bbc.co.uk/programmes/p00h9lkv Science and the Nation]'' The BBC [http://www.bbc.co.uk/reithlectures Reith Lectures], 1956, by Edward Appleton
* {{cite web|last=Davis|first=Chris|title=Treasure in the Basement|url=http://www.backstagescience.com/videos/basement_treasures.html|work=Backstage Science|publisher=[[Brady Haran]]}}
 
{{s-start}}
{{s-aca}}
{{succession box | before=[[John Fraser (educator)|Sir John Fraser]]|title=[[Edinburgh University Principals|Principals of Edinburgh University]] | years=1948–1965| after=[[Michael Swann]]}}
{{s-end}}
{{Nobel Prize in Physics Laureates 1926–1950}}
{{IEEE Medal of Honor Laureates 1951–1975}}
 
{{Authority control|VIAF=54941774}}
 
{{Persondata <!-- Metadata: see [[Wikipedia:Persondata]]. -->
| NAME              = Appleton, Edward Victor
| ALTERNATIVE NAMES =
| SHORT DESCRIPTION =English physicist
| DATE OF BIRTH    = 6 September 1892
| PLACE OF BIRTH    = [[Bradford]], [[West Yorkshire]], [[England]]
| DATE OF DEATH    = 21 April 1965
| PLACE OF DEATH    = [[Edinburgh]], [[Scotland]]
}}
{{DEFAULTSORT:Appleton, Edward Victor}}
[[Category:1892 births]]
[[Category:1965 deaths]]
[[Category:Academics of King's College London]]
[[Category:Fellows of King's College London]]
[[Category:Academics of the University of London]]
[[Category:Alumni of St John's College, Cambridge]]
[[Category:Alumni of the University of Edinburgh]]
[[Category:English academics]]
[[Category:English physicists]]
[[Category:Fellows of the Royal Society]]
[[Category:IEEE Medal of Honor recipients]]
[[Category:Knights Grand Cross of the Order of the British Empire]]
[[Category:Nobel laureates in Physics]]
[[Category:People from Bradford]]
[[Category:Principals of the University of Edinburgh]]
[[Category:Royal Medal winners]]
[[Category:Knights Commander of the Order of the Bath]]
[[Category:Recipients of King Haakon VII's Cross of Liberty]]
[[Category:Honorary Fellows of the Royal Society of Edinburgh]]
[[Category:Fellows of the American Academy of Arts and Sciences]]
[[Category:English Nobel laureates]]

Revision as of 15:20, 29 November 2013

Template:Use British English 30 year-old Entertainer or Range Artist Wesley from Drumheller, really loves vehicle, property developers properties for sale in singapore singapore and horse racing. Finds inspiration by traveling to Works of Antoni Gaudí. Template:Infobox scientist

Sir Edward Victor Appleton, GBE, KCB, FRS[1] (6 September 1892 – 21 April 1965) was an English physicist.[2][3][4][5][6][7][8]

Biography

Appleton was born in Bradford, West Yorkshire, and educated at Hanson Grammar School. At the age of 18 he won a scholarship to St John's College, Cambridge. He graduated with a first class degree in Natural Sciences.

During the First World War he joined the West Riding Regiment, and later transferred to the Royal Engineers. After returning from active service in World War I, Appleton became assistant demonstrator in experimental physics at the Cavendish Laboratory in 1920. He was professor of physics at King's College London (1924–36) and professor of natural philosophy at the University of Cambridge (1936–39). From 1939 to 1949 he was secretary of the Department of Scientific and Industrial Research. Knighted in 1941, he received the 1947 Nobel Prize in Physics for his contributions to the knowledge of the ionosphere,[9] which led to the development of radar.

From 1949 until his death in 1965, he was Principal and Vice-Chancellor of the University of Edinburgh.[10] In 1956, the BBC invited him to deliver the annual Reith Lectures. Across a series of six radio broadcasts, titled Science and the Nation, Appleton explored the many facets of scientific activity in Britain at the time.

Works

Appleton had observed that the strength of the radio signal from a transmitter 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 that it varied during the night. This led him to believe that it was possible that two radio signals were being received. One was travelling along the ground, and another was 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 existence of a reflecting atmospheric layer was not in itself a completely new idea. Balfour Stewart had suggested the idea in the late nineteenth century to explain rhythmic changes in the earth’s magnetic field. More recently, in 1902, Oliver Heaviside and A. E. Kennelly had suggested such a hypothesis 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 empty space before they reached the receiver.

Appleton thought the best place to look for evidence of the ionosphere was in the variations he believed it was causing around sunset in radio signal receptions. 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 and the second was to calculate the angle of arrival of the reflected signal at the receiving aerial.

The frequency modulation 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:

hh=D

The wavelength of the transmitted signal is λ . The number of wavelengths difference between the paths h and h’ is:

hhλ=Dλ=N

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. The means that for our new value λ’, our new value N’ is an also an integer number. If we have lengthened λ then we know that N’ is one less than N. Thus:

NN=DλDλ=1

Rearranging for D gives:

D=hh=11λ1λ

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 colleagues 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 100 km from Cambridge in those days.

This frequency modulation method revealed that the point from which waves were being reflected was approximately 90 km. However, it did not establish that the waves were reflected from above, indeed they may have been coming from hills somewhere between Oxford and Bournemouth. The second method, which involved finding the angle of incidence of the reflected waves at the receiver, showed for sure that they were coming from above. Triangulations from this angle gave results for the height of reflection compatible with the frequency modulation method. We will not go into this method in detail because it involves fairly complex calculations using Maxwell’s electromagnetic theory.

Far from being conclusive, the success of the Oxford-Bournemouth experiment revealed a vast new field of study to be explored. It showed that there was indeed a reflecting layer high above the earth but it also posed many new questions. What was the constitution of this layer, how did it reflect the waves, was it the same all over the earth, why did its effects change so dramatically between day and night, did it change throughout the year? Appleton would spend the rest of his life answering these questions. He developed a magneto-ionic theory based on the previous work of Lorentz and Maxwell to model the workings of this part of the atmosphere. Using this theory and further experiments, he showed that the so-called Kennelly-Heaviside layer was heavily ionised and thus conducting. This led to the term ionosphere. He showed free electrons to be the ionising agents. He discovered that the layer could be penetrated by waves above a certain frequency and that this critical frequency could be used to calculate the electron density in the layer. However these penetrating waves would also be reflected back, but from a much higher layer. This showed the ionosphere had a much more complex structure than first anticipated. The lower level was labelled E – Layer, reflected longer wavelengths and was found to be at approximately 125 km. The high level, which had much higher electron density, was labelled F – Layer and could reflect much shorter wavelengths that penetrated the lower layer. It is situated 300 – 400 km above the earth’s surface. It is this which is often referred to as the Appleton Layer as is responsible for enabling most long range short wave telecommunication.[11]

The magneto-ionic theory also allowed Appleton to explain the origin of the mysterious fadings heard on the radio around sunset. During the day, the light from the sun causes the molecules in the air to become ionised even at fairly low altitudes. At these low altitudes, the density of the air is great and thus the electron density of ionised air is very large. Due to this heavy ionisation, there is strong absorption of electromagnetic waves caused by ‘electron friction’. Thus in transmissions over any distance, there will be no reflections as any waves apart from the one at ground level will be absorbed rather than reflected. However, when the sun sets, the molecules slowly start to recombine with their electrons and the free electron density levels drop. This means absorption rates diminish and waves can be reflected with sufficient strengths to be noticed, leading to the interference phenomena we have mentioned. For these interference patterns to occur though, there must not simply be the presence of a reflected wave but a change in the reflected wave. Otherwise the interference is constant and fadings would not be heard. The received signal would simply be louder or softer than during the day. This suggests the height at which reflection happens must slowly change as the sun sets. Appleton found in fact that it increased as the sun set and then decreased as the sun rose until the reflected wave was too weak to record. This variation is compatible with the theory that ionisation is due to the sun’s influence. At sunset, the intensity of the sun’s radiation will be much less at the surface of the earth than it is high up in the atmosphere. This means ionic recombination will progress slowly from lower altitudes to higher ones and therefore the height at which waves are reflected slowly increases as the sun sets.

The basic idea behind Appleton’s work is so simple that it is hard to understand at first how he devoted almost all of his scientific career to its study. However, in the last couple of paragraphs some of the complexities of the subject have been introduced. Like many other fields, it is one that grows in intricacy the more it is studied. By the end of his life, ionospheric observatories had been set up all over the world to provide a global map of the reflecting layers. Links were found to the 11 year sunspot cycle and the Aurora Borealis, the magnetic storms that occur in high latitudes. This became particularly relevant during the second world war when the storms would lead to radio blackouts. Thanks to Appleton’s research, the periods when these would occur could be predicted and communication could be switched to wavelengths that would be least affected. RADAR, another crucial wartime innovation, was one that came about thanks to Appleton’s work. On a very general level, his research consisted in determining the distance of reflecting objects from radio signal transmitters. This is exactly the idea of RADAR and the flashing dots that appear on the screen (a cathode ray tube) scanned by the circulating ‘searcher’ bar. This system was developed partly by Appleton as a new method, called the pulse method, to make ionospheric measurements. It was later adapted by Robert Watson-Watt to detect aeroplanes. Nowadays, ionospheric data is important when communications with satellites are considered. The correct frequencies for these signals must be selected so that they actually reach the satellites without being reflected or deviated before.

In 1974 the Radio and Space Research Station was renamed the Appleton Laboratory in honour of the man who had done so much to establish the UK as a leading force in ionospheric research, and had been involved with the station first as a researcher and then as secretary of its parent body, the Department of Scientific and Industrial Research.

Honours and awards

Appleton was awarded the following:

In addition the following are named in his honour:

References

43 year old Petroleum Engineer Harry from Deep River, usually spends time with hobbies and interests like renting movies, property developers in singapore new condominium and vehicle racing. Constantly enjoys going to destinations like Camino Real de Tierra Adentro.

Further reading

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