George Paget Thomson-Nobel Lecture Ever since last Novem ber, I have been wanting to ex press in person my gratit ude to the generas ity of Alfred Nobel, to w hom i ow e it t hat I am privileged be here today, es pecial y since ill ness prevented me from doi ng so at the proper time. the idealism w hic h permeated his char acter led him to make his magnifice nt foundation for the benefit of a cl ass of men with w hose aims and view poi nt his ow n scienti fic instincts and a bility had made him naturally his successful in the first as in t he second, is due to the manner in w hich his wishes have been carried out. The Sw edis h peo ple under the le adershipof the Royal Family, and through the medium of the Royal Academy of Sciences, have made the Nobel Prizes one of the chief causes of the growth of the prestige of science in the eyes of the world, w hich is a feat ure of our time. As a recipient of Nobel's generosity I ow e since rest thanks to them as well as The goddess of le ning is fa bled to have s rung full -grow n from the brain o Zeus, but it is seldom that a scientific conce ption is born in its final form or owns a single parent. More often it is the product of a series of minds, each in turn modifying the ideas of those that came before, and providing material for those that come after. The electron is no exception. have realized it, his wor k on electrol ysis, by s howing the o uti the first step. Clerk Maxwell in 1873 used t he phrase a 'molec ule of electricity and von Helmholtz in 1881 s pea king of Faradays wor k said "If we accept the hypothesis that elementary substances are composed of atoms, we cannot well avoid concluding that electricity also is div ided into elementary porti ons w hich behave like atoms of electricity. The hypothetical atom received a name in the same year when Johnstone Stoney of Dublin christened lectron charge. last year of the nineteenth century saw the electron take a leading place amongst the conceptions of physics. It acquired not only mass but uni versality, it was not only electricity but an essential part of all matter. If among the many names associated with this advance I mention hat of].J. Thomson I hope you will forgi ve a nat ural pride. It is tothe great work of Bohr that we owe the demonstration of the connection between electrons and antum whic h gave the electron a dy namics of its own. A few years later, Goudsmit and Uhlenbeck, following on an earlier s ug gestion by A.H. pt on s how ed that it was necessary to suppose that the electron had s pin. Yet even with the properties of char ge, mass, s pin and a s pecial mechanics to help it, the electron was unable to carry the burden of explaining the large and detailed ch had accumulated. L. heory of radiation, associated with a system of w aves. It is with these w aves, formul ated more precisely by Schr tt inger, and modified by Dirac to cover the idea of s pin, rest of my lecture will deal The first published experiments to confim de Broglie,s theory were thase of Davisson and Germer, but perhaps you will allow me to describe instead those to which my pupils and I were led by de Broglie,s epoch-making conception. A narrow beam of cathode r ays was transmitted through a thin film of matter. In the earliest ex periment of the late Mr. Reid this film was of cellu oid, in my ow n experiment of metal. In both, the thickness was of the order of 10cm. The scatte red beam was received on a phot ogr aphic plate normal the beam, and when developed showed a pattern o rings, recalling optical halos and the Debye-Scherrer rin ence phe nomenon is at once suggested. This would occur if each atom of the fllm scatter ed in phase a wavelet from an advancing wave associated with the electrons formi ng the cat hode rays. since the atoms in each small crystal ofthe metal are regul arly spaced, the phases of the wavel ets scattered in ay fixed direction will have a definite rel ationshi pto one another. In some directions they will agree in phase and uild up a str ong scattered wave, in others they will destroy one anot her by interference. the strong wav es are analogous to the beams of light diffracted by an optical grating. At the time, the arm angem ent of the at oms in cellul oid was not known with certai nty and only general concl usions could be drawn, but for t he m etals it had been determined previously by the use of x-rays. Accor ding to de Broglie's theory the wavelengt h ass ociated with an electron is hmv w hic h for the electrons used(cat hode oto 60,000 wolts energy )comes out from 8 X 10-to 5x 10-cm. I do not wishto trouble you with detail ed figures and it will be enough to say t hat the patterns on the photogr aphic pl ates agreed quantitatively, in all cases, withGeorge Paget Thomson – Nobel Lecture Nobel Lecture, June 7, 1938 Electronic waves Ever si nce l ast Novem ber, I hav e been wanting to express i n person my gratit ude to t he generosit y o f Alfr ed Nobel, to w hom I ow e it t hat I am privileged to be her e t oday, es peciall y si nce ill ness pr evented m e from doi ng so at t he pr oper tim e. The idealism w hic h perm eated his c har acter l ed him to make his magni ficent foundation for t he bene fit o f a cl ass of men with w hose aims and view poi nt his ow n scienti fic insti ncts and ability had m ade him natur ally sympat hetic, but he was c ertai nly at least as muc h concer ned wit h hel ping science as a w hol e, as i ndi vidual scientists. That his foundation has been as successful in t he first as in t he second, is due to t he manner i n w hich his wishes hav e been carri ed out. The Sw edis h people, under the leade rshi p o f t he Royal Family, and through the medium of the Royal Academy of Sciences, have made the Nobel Prizes one of the chief causes of the growth of the prestige o f science i n t he eyes o f the worl d, w hich is a feat ure o f our tim e. As a r ecipi ent of Nobel's generosity I ow e since rest thanks to t hem as w ell as to him. The goddess o f lear ning is fabled t o have s pr ung full -gr ow n from the brai n of Zeus, but it is sel dom that a scienti fic conception is born in its final form, or owns a single parent. More often it is the product of a series of minds, each in turn modifying the ideas of those that came before, and providing material for those that come after. The electron is no exception. Although F araday does not seem to have r ealized it, his wor k on electrol ysis, by s howi ng the unit ary c har acter of t he charges on at oms i n sol ution, was the first step. Cle rk M axwell i n 1873 used t he phrase a "m olec ule of electricity" and von Helmholtz in 1881 s pea king of F araday's wor k said "I f we accept the hypothesis that elementary substances are composed of atoms, we cannot well avoid concluding that electricity also is divided into elementary porti ons w hich behav e lik e atoms of electricity." The hypothetical at om r eceiv ed a name i n the sam e y ear when Johnstone St oney of Dublin christened it "electron", but so far the only property implied was an electron charge. The last year of the nineteenth century saw the electron take a leading place amongst the conceptions of physics. It acquired not only mass but uni versalit y, it was not only el ectricity but an essential part o f all m atter. I f among the m any nam es associat ed with this advance I mention t hat o f J.J. Thomson I hope you will forgi ve a nat ural pri de. It is t o t he great wor k o f B ohr that we owe the demonstrati on o f the connection between electr ons and Planc k's quantum whic h gav e the el ectron a dynamics of its ow n. A few y ears l ater, Goudsmit and Uhlenbeck, foll owing on an earli er s ug gestion by A.H. Compt on s how ed t hat it was necessar y to suppose t hat t he el ectron had s pin. Yet ev en wit h the pr operties o f char ge, mass, s pin and a s pecial m echanics to help it, the electron was unable to carry the burden of explaining the large and detailed mass of experimental data which had accumulated. L. de Brogli e, wor king origi nall y on a t heory of radiati on, produced as a ki nd o f by-pr oduct the conception t hat any particle and i n partic ular an el ectron, was associated wit h a system o f w aves. It is with these w av es, formul ated m ore pr ecisely by Schr 鰀 inger, and modifi ed by Dirac t o cover the i dea o f s pin, that the rest of my lecture will deal. The first published experiments to confirm de Broglie's theory were those of Davisson and Germer, but perhaps you will allow me to describe instead those to which my pupils and I were led by de Broglie's epoch-making conception. A narrow beam o f c athode r ays w as transmitted t hrough a thi n film o f m atter. I n t he earliest experim ent o f t he late Mr. Reid t his film w as o f c ellul oid, in my ow n experiment of metal. In bot h, t he t hickness was of the orde r o f 10-6 cm. The scatte red beam was r eceiv ed on a phot ogr aphic plate normal to the beam, and when developed showed a pattern of rings, recalling optical halos and the Debye-Scherrer rings well known in the corresponding experiment wit h X-r ays. A n i nterference phenom enon is at onc e suggested. This would occur if eac h atom of the film scatter ed i n phase a wavel et fr om an advancing wave associated wit h t he electrons formi ng the cat hode r ays. Si nce t he atoms i n each small cr ystal o f t he metal are regul arly spac ed, t he phases of the wavel ets scattered i n any fix ed di rection will have a defi nite rel ationshi p t o one anothe r. In som e directions t hey will agree i n phase and buil d up a str ong scattered wave, in others t hey will destroy one anot her by int erference. The strong wav es are analogous to t he beams o f li ght diffracted by an optic al gr ating. At t he tim e, the arr angem ent of the at oms in cellul oid was not known with c ertai nty and only general c oncl usions could be dr awn, but for t he m etals it had been determi ned pre viously by the use of X-rays. Accor ding to de Br ogli e's theor y t he w av elengt h ass ociated wit h an electron is h/mv w hic h for the el ectrons used (cat hode rays of 20 to 60,000 volts ener gy ) comes out fr om 8 X 10- 9 to 5 X 10- 9 cm. I do not wish t o troubl e you wit h detail ed figures and it will be enough to say t hat t he patter ns on the photogr aphic pl ates agreed quantitati vely, i n all cases, with t he distribution o f str ong