January 19, 1922] 



NATURE 



67 



of the reception and speedy appreciation of the 

 discovery in England. For in a quarter of a cen- 

 tury a new generation of physicists has arisen, many 

 of them so intently occupied with their own admir- 

 able investigations that perhaps the origin of much 

 of our present knowledge of Nature is liable to be 



tibmerged. Especially may they fail to realise the 



iiticipations of the great theorists, which enabled 

 ■ little seed -fact to fit immediately into its cranny 



iid quickly to develop magnificent blossoms. 

 As to its reception here, the begiiining was 



xtremely modest, and may be narrated thus: 

 ()n December 24, 1896, there appeared in 

 Nature, vol. 55, p. 192, the usual report of a 

 meeting of the Royal Academy of Sciences of 

 Amsterdam, and in a paragraph abstracting a 

 number of other communications to that society the 

 following sentence occurs : — 



" Prof. Kamerlingh Onnes communicated two 

 papers : (a) by Dr. Zeeman, on the influence of 

 magnetisation on the nature of the light emitted by 

 a substance. Pursuing a hint given by Faraday, 

 several experiments were tried. The principle was 

 this : the light of the electric arc, being sent 

 through a heated tube containing sodium vapour, 

 is analysed by a Rowland's grating. The tube is 

 placed between the poles of an electro-magnet. 

 When acted on by the magnet, a slight broadening 

 of the two sodium lines is seen, tending to show 

 that forced vibrations are produced in the atoms 

 by the action of magnetism; {h) by Dr. J. Ver- 

 schaffelt on capillary a.scent," etc. 



This sentence, included in a long paragraph, was 

 probably the first announcement in England ; but it 

 was so inconspicuous that it coiild scarcely have 

 attracted much attention, had not Sir Joseph 

 Larmor, this year's Copley medallist, been on the 

 look-out for an effect of this kind. He had previ- 

 ously perceived that such a result was necessary 

 theoretically ; a fact which is demonstrated by, 

 among other things, the following passage repro- 

 duced on p. 203 of his book, " .^^ther and 

 Matter " : — 



" Each absorption line say of sodium vapour in 

 a magnetic field will thus be more or less widened, 

 and its main position also slightly shifted but only 

 to a higher order of small quantities : and the 

 same will apply to each line in the emission spec- 

 trum." 



Larmor had indeed gone on to calculate the 

 amount of displacement or broadening to be ex- 

 pected, and had found the effect too small to be 

 observed ; for, like everyone else at that time, he 

 considered that the radiating body must be an atom 

 or part of an atom with an ^/w=io*. So directly 

 Zeeman got an effect, and found that the e\m was 

 really of the order 10'^, I.armor perceived that, not 

 the whole atom, but the charge only — the electron 

 NO. 2725, VOL. 109] 



part of the ion, or an electron itself — was a free 

 radiator, and wrote to me suggesting that I should 

 examine and confirm the result. In a week I had 

 done so, with such appliances as were to hand ; 

 though not without sufficient difficulty to make me 

 realise the naturalness of Faraday's failure to see 

 anything — he being wholly unguided by theory — 

 and to admire the skill of Zeeman in detecting the 

 effect. 



Prof. Zeeman must soon afterwards have com- 

 municated his observations to the Physical Society 

 of Berlin; for in Nature, vol. 55, p. 347. is a 

 translation of a short paper by him, dated from 

 Amsterdam and thanking Prof. K. Onnes for his 

 interest in the work. 



The first official notice in England occurs in the 

 Proceedings of the Royal Society for February 11, 

 1897, when a note by me entitled " The Influence 

 of a Magnetic Field on Radiation Frequency " was 

 received and read on the same day. It gives an 

 account of my repetition of Zeeman's experiment 

 and directs attention to Prof. Lorentz's theory of it, 

 together with his brilliant prediction about polarisa- 

 tion of the modified lines, and its experimental 

 verification (see Proc. Roy. Soc., vol. 60, p. 513)- 

 It is followed, on p. 514, by a theoretical note by 

 Sir Joseph Larmor, in which he emphasises the 

 " electron " aspect of the matter, and its reciprocal 

 relation to Faraday's first magneto-optic effect. He 

 also directs attention to previous memoirs by Helm- 

 holtz in 1893, and by Lorentz in 1892 and 1895, 

 especially the former; and he cites p. 813 of his 

 own splendid Memoir in Phil. Trans., A, 1894. 



I also communicated a much longer article to 

 the Electrician for February 26, 1897, vol, 38, 

 p. 568, under the heading, " The Latest Discovery 

 in Physics": an article which I should like to 

 reproduce' here, for I venture to say that portions 

 of it are worthy of reference by anyone interested 

 in scientific history. The freedom with which we 

 all spoke of electrons and their motions m those 

 days rather surprises me, seeing that the unit charge 

 was not isolated and clinched until 1899. But, of 

 course, the theoretical work of Dr. Johnstone 

 Stoney and others had long preceded this date- 

 There was no excuse for not fully understandmg 

 the main perturbations of spectrum lines when once 

 the idea of electrons revolving like satellites m 

 regular orbits, obedient to astronomical laws, had 

 been grasped; for Dr. Johnstone Stoney's remark- 

 able paper, entitled "On the Cause of Double 

 Lines and of Equidistant Satellites in the Spectra 

 of Gases," was in my possession. (It will be found 

 in the Transactions of the Royal Dublin Society 

 for 1891, vol. 4, Series II., pp. 563-608.) 



But the difficulty was that at that date we all— 



