Award Ceremony Speech
Presentation Speech by Professor H. Pleijel, Chairman of the Nobel Committee for Physics of the Royal Swedish
Academy of Sciences, on December 10, 1930
Your Majesty, Your Royal Highnesses, Ladies and Gentlemen.
The Academy of Sciences, has resolved to award the Nobel Prize in Physics for 1930 to Sir Venkata Raman
for his work on the scattering of light and for the discovery of the effect named after him.
The diffusion of light is an optical phenomenon, which has been known for a long time. A ray of light is not
perceptible unless it strikes the eye directly. If, however, a bundle of rays of light traverses a medium in
which extremely fine dust is present, the ray of light will scatter to the sides and the path of the ray through
the medium will be discernible from the side. We can represent the course of events in this way; the small
particles of dust begin to oscillate owing to electric influence from the ray of light, and they form centres from
which light is disseminated in all directions. The wavelength, or the number of oscillations per second, in the
light thus diffused is here the same as in the original ray of light. But this effect has different degrees of
strength for light with different wavelengths. It is stronger for the short wavelengths than for the long ones,
and consequently it is stronger for the blue part of the spectrum than for the red part. Hence if a ray of light
containing all the colours of the spectrum passes through a medium, the yellow and the red rays will pass
through the medium without appreciable scattering, whereas the blue rays will be scattered to the sides.
This effect has received the name of the "Tyndall effect".
Lord Rayleigh, who has made a study of this effect, has put forward the hypothesis that the blue colours of
the sky and the reddish colouring that is observed at sunrise and sunset is caused by the diffusion of light
owing to the fine dust or the particles of water in the atmosphere. The blue light from the sky would thus be
light-scattered to the sides, while the reddish light would be light that passes through the lower layers of the
atmosphere and which has become impoverished in blue rays owing to scattering. Later, in 1899, Rayleigh
threw out the suggestion that the phenomenon in question might be due to the fact that the molecules of air
themselves exercised a scattering effect on the rays of light.
In 1914 Cabannes succeeded in showing experimentally that pure and dustless gases also have the
capacity of scattering rays of light.
But a closer examination of scattering in different substances in solid, liquid, or gaseous form showed that
the scattered light did not in certain respects exactly follow the laws which, according to calculation, should
hold good for the Tyndall effect. The hypothesis which formed the basis of this effect would seem to involve,
amongst other things, that the rays scattered to the sides were polarized. This, however, did not prove to be
exactly the case.
This divergence from what was to be expected was made the starting point of a searching study of the
nature of scattered light, in which study Raman was one of those who took an active part. Raman sought to
find the explanation of the anomalies in asymmetry observed in the molecules. During these studies of his in
the phenomenon of scattering, Raman made, in 1928, the unexpected and highly surprising discovery that
the scattered light showed not only the radiation that derived from the primary light but also a radiation that
contained other wavelengths, which were foreign to the primary light.
In order to study more closely the properties of the new rays, the primary light that was emitted from a
powerful mercury lamp was filtered in such a way as to yield a primary light of one single wavelength. The
light scattered from that ray in a medium was watched in a spectrograph, in which every wavelength or
frequency produces a line. Here he found that, in addition to the mercury line chosen, there was obtained a
spectrum of new sharp lines, which appeared in the spectrograph on either side of the original line. When
another mercury line was employed, the same extra spectrum showed itself round it. Thus, when the
primary light was moved, the new spectrum followed, in such a way that the frequency distance between the
primary line and the new lines always remained the same.
Raman investigated the universal character of the phenomenon by using a large number of substances as a
scattering medium, and everywhere found the same effect.
The explanation of this phenomenon, which has received the name of the "Raman effect" after its
discoverer, has been found by Raman himself, with the help of the modern conception of the nature of light.
According to that conception, light cannot be emitted from or absorbed by material otherwise than in the
form of definite amounts of energy or what are known as "light quanta". Thus th
Award Ceremony SpeechPresentation Speech by Professor H. Pleijel, Chairman of the Nobel Committee for Physics of the Royal SwedishAcademy of Sciences, on December 10, 1930Your Majesty, Your Royal Highnesses, Ladies and Gentlemen.The Academy of Sciences, has resolved to award the Nobel Prize in Physics for 1930 to Sir Venkata Ramanfor his work on the scattering of light and for the discovery of the effect named after him.The diffusion of light is an optical phenomenon, which has been known for a long time. A ray of light is notperceptible unless it strikes the eye directly. If, however, a bundle of rays of light traverses a medium inwhich extremely fine dust is present, the ray of light will scatter to the sides and the path of the ray throughthe medium will be discernible from the side. We can represent the course of events in this way; the smallparticles of dust begin to oscillate owing to electric influence from the ray of light, and they form centres fromwhich light is disseminated in all directions. The wavelength, or the number of oscillations per second, in thelight thus diffused is here the same as in the original ray of light. But this effect has different degrees ofstrength for light with different wavelengths. It is stronger for the short wavelengths than for the long ones,and consequently it is stronger for the blue part of the spectrum than for the red part. Hence if a ray of lightcontaining all the colours of the spectrum passes through a medium, the yellow and the red rays will passthrough the medium without appreciable scattering, whereas the blue rays will be scattered to the sides.This effect has received the name of the "Tyndall effect".Lord Rayleigh, who has made a study of this effect, has put forward the hypothesis that the blue colours ofthe sky and the reddish colouring that is observed at sunrise and sunset is caused by the diffusion of lightowing to the fine dust or the particles of water in the atmosphere. The blue light from the sky would thus belight-scattered to the sides, while the reddish light would be light that passes through the lower layers of theatmosphere and which has become impoverished in blue rays owing to scattering. Later, in 1899, Rayleighthrew out the suggestion that the phenomenon in question might be due to the fact that the molecules of airthemselves exercised a scattering effect on the rays of light.In 1914 Cabannes succeeded in showing experimentally that pure and dustless gases also have thecapacity of scattering rays of light.But a closer examination of scattering in different substances in solid, liquid, or gaseous form showed thatthe scattered light did not in certain respects exactly follow the laws which, according to calculation, shouldhold good for the Tyndall effect. The hypothesis which formed the basis of this effect would seem to involve,amongst other things, that the rays scattered to the sides were polarized. This, however, did not prove to beexactly the case.This divergence from what was to be expected was made the starting point of a searching study of thenature of scattered light, in which study Raman was one of those who took an active part. Raman sought tofind the explanation of the anomalies in asymmetry observed in the molecules. During these studies of his in the phenomenon of scattering, Raman made, in 1928, the unexpected and highly surprising discovery thatthe scattered light showed not only the radiation that derived from the primary light but also a radiation thatcontained other wavelengths, which were foreign to the primary light.In order to study more closely the properties of the new rays, the primary light that was emitted from apowerful mercury lamp was filtered in such a way as to yield a primary light of one single wavelength. Thelight scattered from that ray in a medium was watched in a spectrograph, in which every wavelength orfrequency produces a line. Here he found that, in addition to the mercury line chosen, there was obtained aspectrum of new sharp lines, which appeared in the spectrograph on either side of the original line. Whenanother mercury line was employed, the same extra spectrum showed itself round it. Thus, when theprimary light was moved, the new spectrum followed, in such a way that the frequency distance between theprimary line and the new lines always remained the same.Raman investigated the universal character of the phenomenon by using a large number of substances as ascattering medium, and everywhere found the same effect.The explanation of this phenomenon, which has received the name of the "Raman effect" after itsdiscoverer, has been found by Raman himself, with the help of the modern conception of the nature of light.According to that conception, light cannot be emitted from or absorbed by material otherwise than in theform of definite amounts of energy or what are known as "light quanta". Thus th
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