Physics 1928 OWEN WILLANS RICHARDSON <<for his work on the thermionic phenomenon and especially-for the discovery of the law named after him>> Physics 1928 Presentation Speech by Professor C. W. Oseen, Chairman of the Nobel Committee for Physics of the Royal Swedish Academy of Sciences Your Majesty, Your Royal Highnesses, Ladies and Gentlemen. Among the great problems that scientists conducting research in electro- technique are today trying to solve, is that of enabling two men to converse in whatever part of the world each may be. In 1928 things had reached the stage when we could begin to establish telephonic communication between Sweden and North America. On that occasion there was a telephone line of more than 22,000 kilometres in length between Stockholm and New York. From Stockholm, speech was transmitted via Berlin to England by means of a cable and overhead lines; from England by means of wireless to New York; then, via a cable and lines by land, over to Los Angeles and back to New York, and from there by means of a new line to Chicago, returning finally to New York. In spite of the great distance, the words could be heard distinctly and this is explained by the fact that there were no fewer than 166 amplifiers along the line. The principle of construction of an amplifier is very simple. A glowing filament sends out a stream of electrons. When the speech waves reach the amplifier, they oscillate in tune with the sound waves but are weakened. The speech waves are now made to put the stream of electrons in the same state of oscillation as they have themselves. So exactly does the stream of electrons adapt itself to the speech waves that the amplification could be repeated 166 times without the distinctness of speech being lost. I should like to give another example of what has recently been attained in that department. On the 16th of February 1928, there was a conference between the American Institute of Electrical Engineers in New York and the Institution of Electrical Engineers in London. The various speeches could be heard in both places by means of loud-speakers. Most people here present will certainly be able to call to mind those anx- ious days, when news of the missing Nobile expedition was awaited all over the world. Everyone will no doubt remember that the first word of the lost expedition was picked up by a wireless amateur. I think that on this occasion it was clear to many people that wireless is not only a means of diversion - and as such, one of the more prominent - but also one of the most valuable 222 PHYSICS 1928 expedients in the struggle against that sort of Nature which is still uncon- quered. Every owner of a valve receiving-set knows the importance of the valve in the apparatus - the valve, the essential part of which is the glowing fila- ment. At the Jubilee, held in the twenty-fifth year of the reign of King Oscar II, our medical men were enabled to take up the struggle against the tuber- culosis, thanks to the Jubilee Fund. At the Jubilee held on Your Majesty’s 70th birthday, the fight against cancer was taken up in the same manner. We all know that Röntgen rays are one of the keenest weapons employed in this struggle. But we know, too, that this weapon is double-edged. The rays cannot only do good but also do harm. All depends on the accurate regula- tion of their strength and intensity. Quite recently, a change has taken place in this department. Röntgen rays are obtained when rapidly moving elec- trons collide with a solid body. By using a glowing filament in order to produce the electron stream, the means of regulating accurately the strength and intensity of Röntgen rays has been obtained. Behind the progress which has here been briefly pointed out, lies the work of many men. But we have seen that they all have one thing in common. A <<red thread>> connects them - the glowing filament. As early as 1737, a French scientist, Du Fay by name, found out that air in proximity to a glowing body is a conductor of electricity. Valuable re- searches concerning the character of this conductivity was made by Elster and Geitel, two German scientists. Their investigations were continued by Mr. J. J. Thomson, the Grand Old Man of English Physics of today. By these researches they have found it probable that the conductivity of air in proximity to a glowing metal depends on electrons in the air, which have been made free in some way or another. So far had the researches advanced when Mr. O. W. Richardson appeared and devoted himself to it. He began by laying down a theory for the phenomenon. According to this theory the phenomenon is bound up with the electrical conductivity of metals. The latter depends on the fact that there are free electrons in a metal. At higher temperatures these cannot, according to Mr. Richardson, be retained by the body but they are emitted according to a fixed law. But a theory alone does not give any knowledge of reality. That can be obtained only by means of experimental research. So Mr. Richardson proceeded to do this. The point was to find out if the theory was really right. The strenuous work of twelve years was necessary to settle this question. So hard was the struggle that even PRESENTATION 223 so late as in the twelfth year, there was a time when it was uncertain whether Mr. Richardson’s theory was not completely wrong, and if the origin of the phenomenon was not quite different, being, for instance, chemical reactions between the metal and impurities in it. But in the end, Mr. Richardson’s the- ory proved to be correct in all essential points. The most important fact was that Mr. Richardson’s opinion about the thermion-phenomenon with fixed laws was totally confirmed. Through this fact a solid basis was obtained for the practical application of the phenomenon. Mr. Richardson’s work has been the starting-point and the prop of the technical activity which has led to the progress of which I have just spoken. Professor Richardson. You are a happy man. You possess the very thing that gives life its chief value. You can devote yourself with all your strength to the activity that you love. We constantly see the results of this activity come to light. Besides this, you are fortunate enough to see the harvest ripen to the benefit of mankind in the fields you tilled in your youth. For one who is so rich it is but a little thing to receive the greatest prize which the Royal Academy of Sciences has at its disposal as a reward for a scientific discovery. I ask you, however, to receive from our King’s hand the Nobel Prize for Physics for the year 1928. OWEN W. RICHARDSON Thermionic phenomena and the laws which govern them Nobel Lecture, December 12, 1929 In its broadest aspect this subject may be summarized as the branch of Phys- ics which deals with the effect of heat on the interaction between electricity and matter. It is not altogether new. Nearly 200 years ago it was known that air in the neighbourhood of hot bodies conducted electricity. In 1873 Guth- rie showed that a red-hot iron ball in air could retain a negative but not a Positive charge. In a series of researches extending from 1882 to 1889, Elster and Geitel examined the charge collected on an insulated plate placed near various hot wires in diverse gases at different pressures. The observed effects were very specific and varied, but there emerged a general tendency for the plate to acquire a positive charge at low temperatures and high pressures, and a negative charge at high temperatures and low pressures. The matter be- came really interesting in 1899 when J. J. Thomson showed that the dis- charge from an incandescent carbon filament in a vacuum tube was carried by negative electrons. In 1900 McClelland showed that the currents from a negatively charged platinum wire were influenced very little, if at all, by changes in the nature and pressure of the surrounding gas, if the pressure were fairly low. These facts seemed to me to be highly significant, and I resolved to investigate the phenomenon thoroughly. The view of these effects generally held at that time by people who had thought about them was that the electric discharges were carried by ions and electrons which were generated by the interaction of the neighbouring gas molecules with the hot body. It was left an open question as to whether this action was merely thermal, a matter of kinetic energy, or was chemical, or involved the intervention of radiation. The effects observed in the best vacua were attributed to the residual gas which could not be got rid of. This was, of course, easily possible. I felt, however, that it was very likely that inter- acting gases had little to do with the main phenomenon, but that the neg- atively charged electrons and, possibly, the positively charged ions too were coming from the heated solid. This would be reasonable from the point of view of the theories of metallic conduction which had been put forward THERMIONIC PHENOMENA/LAWS WHICH GOVERN THEM 225 between 1888 and 1900 by Thomson, Riecke, and Drude. I decided that the best way to make progress was to get rid of the complications due to the presence of gases and to find out what, if anything, happened when gas ef- fects were excluded.