NATURE 



505 



THURSDAY, SEPTEMBER 21, 1905. 



THE EVOLUTION OF MATTER. 

 L'Evohition de La Matiere. By Dr. Gustave Le Bon. 

 Pp. 3S9. (Paris: Flammarion, 11105.) Price 3.50 

 francs. 



DR. GUSTAVE LE BON has written many boolis. 

 Some twenty volumes, besides papers in current 

 scientific periodical literature, have issued from his 

 pen. History, travels, tobacco-smoke, anthropology, 

 horsemanship, and psychology have in turn attracted 

 his sympathetic interest. 



The work before us sets forth Dr. Le Bon's theories 

 of matter and energy, and contains, in a small-print 

 appendi.x, an abstract of the experimental evidence 

 on w^hich he is content to rest those theories. 



According to the author, matter itself is merely 

 a form of energy — probably vortex energy in the 

 luminiferous aether. Matter disintegrates— spon- 

 taneously in radio-active substances, but also under 

 the influence of certain agencies such as heat or 

 chemical action, which are compared with the spark 

 that. fires a barrel of gunpowder. After giving rise 

 to " les produits de la dematiSriallsation de la matiere : 

 ions, electrons, rayons cathodiques, &c.," all things 

 finally pass into " I'^l^ment immat^riel de I'univers : 

 1' Ether. " By the dissociation of matter, energy is 

 transformed, and " c'est de I'^nergie intra-atomique 

 lib^rte par la dematerialisation de la matiere que 

 derivent la plupart des forces de I'univers." 



The chief experimental evidence on which Dr. 

 Le Bon relies may be grouped under two heads : — 

 (i) the emission of negatively electrified particles by 

 metals when incandescent and when subjected to the 

 action of ultra-violet light ; (2) the slight radio-activity 

 which may be detected in ordinary materials. 



The emission of negative corpuscles from metals 

 under the influence of heat and light undoubtedly 

 occurs, though it is not to the author's speculative 

 opinions that we owe the experimental demonstration 

 of the fact. As a speculative hypothesis, the idea that 

 the corpuscles are emitted during the disintegration 

 of the atoms of the metal is perhaps worth bearing 

 in mind. But, on a review of the evidence known at 

 present, it seems unlikely that the removal of these 

 slow-moving negative corpuscles results in the in- 

 stability of the atom from which they are derived. 

 There is no evidence that an electric discharge 

 through a gas produces new elements, while the ions 

 of liquids and gases, which result from the removal 

 of the corpuscle, again yield the original atom when 

 neutralised. .Such processes are to be distinguished 

 sharply from the irreversible changes which occur in 

 true radio-activity, when bodies of atomic mass 

 (a rays) or fast-moving corpuscles {$ rays) are pro- 

 jected. In this case, new chemical substances always 

 appear, and the process seems to be unaffected by 

 heat, light, or any other physical or chemical agency. 

 This essential distinction is not noticed by Dr. 

 Le Bon, who assumes that the production of a cor- 

 puscle is itself a proof of atomic disintegration. 



The author claims that he was the first to show 

 NO. 1873, VOL, 72 j 



that radio-activity is a universal phenomenon, not 

 confined to a few substances : — 



" Mon premier memoire sur la radio-activite de 

 tous les corps sous Taction de la lumifere a paru dans 

 la Revue Scientifiqiie de mai 1897. Celui sur la 

 radio-activite par les actions chimiques a iti public 

 en avril 1900. Celui montrant la radio-activite 

 spontan^e des corps ordinaires a paru — toujours dans 

 la meme revue — en novcmbre 1902. Les premieres 

 experiences par lesquelles les physiciens aient cherch^ 

 h prouver que la radio-activite pouvait s'observer avec 

 des corps autres que 1 'uranium, le thorium et le 

 radium n'ont et^ publlees par Strutt, McLennan, 

 Burton, &c., que de juin a aout 1903." 



We may first notice that Dr. Le Bon classes the 

 effects of light under the head of radio-activity. This, 

 it may be argued, is a matter of definition, and the 

 author is at liberty to give a meaning to the word 

 radio-activity different from that adopted by all other 

 physicists. But it is well to point out that many 

 experiments on the electric effects of the incidence of 

 light on metals had been made before the year 1897, 

 notably by Elster and Geitel between 1889 and 1895. 

 Dr. Le Bon may have been the first to suggest that 

 the effects were due to the emission of particles, but 

 no conclusive evidence was obtained until the experi- 

 ments of J. J. Thomson and Lenard, in 1899, had 

 determined the ratio of the charge to the mass, and 

 identified the particles with those found in kathode 

 rays. 



Secondly, doubt has been thrown on the emission 

 of rays by substances undergoing chemical action by 

 the recent experiments of Mr. N. R. Campbell, who 

 has traced some, at all events, of the effects to 

 secondary causes connected with the heat of reaction. 

 Here Dr. Le Bon does not seem always to separate 

 clearly the ionisation which may be produced in a gas 

 by contact with substances undergoing chemical 

 change, and the emission of radiations, more or less 

 penetrating, characteristic of true radio-activity. 



Thirdly, in examining the spontaneous radio-activity 

 of ordinary materials, the author seems to under- 

 estimate the effect of the minute traces of radium 

 which are now known to be distributed widely. He 

 claims Prof. J. J. Thomson's experiments on the 

 emanations emitted by various natural substances and 

 underground waters as a confirmation of his view that 

 all matter is radio-active. Now, Thomson found that 

 the rate of decay and the phenomena of excited 

 activity in those emanations which he examined 

 closely were about the same as those of the radium 

 emanation, and his experiments should be regarded 

 as an indication of the prevalence of radium rather 

 than of the radio-activity of ordinary materials. It 

 is true that further experiments by Thomson, Cooke, 

 Campbell, Wood, and others have now made it prob- 

 able that ordinary metals, at all events, are slightly 

 radio-active. But, to eliminate the effects of strongly 

 radio-active impurities, it is necessary to take the 

 utmost precautions, both in the experiments them- 

 selves and still more in the interpretation of the 

 results. There seems little evidence that, in either 

 respect, Dr. Le Bon recognised the necessity of such 

 precautions. 



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