PHYSICS, PROGRESS OF, IN 1902. 



551 



urn, which would experience cooling, or it might 

 be furnished from radiations with which we are 

 not acquainted or from other unknown sources. 

 P. de Keen (Revue Scientifique, Aug. 10, 1901) 

 states that nearly all foci of disturbance of the 

 ether, such as flames, brush discharges, hot bod- 

 ies, electric sparks, radio-active substances, etc., 

 produce an emanation comparable to that of a 

 Crookes tube; and when this reaches a surface 

 the action is distributed on the surface just as 

 a jet of elastic liquid would be. It is as if these 

 foci emitted ether, which, on encountering matter 

 of sufficiently small density, carried it along me- 

 chanically. When a thick card coated with a 

 mixture of colophane and wax is first electrified 

 by rubbing, then exposed to the actions under 

 study, and finally dusted with sulfur, figures are 

 developed which show the distribution of the 

 charge on this plate. The charge has been driven 

 into positions the same as those into which 

 liquid would have been heaped up by a jet or jets. 

 A long series of very curious experiments of this 

 order is described under the influence of flames, 

 brush discharges, sparks, radio-active substances, 

 superficial chemical activity, surfaces modified by 

 the impact of light, Rontgen rays, and incandes- 

 cent bodies. As with heat, there seems to be 

 both conduction and radiation, but the radiation 

 originates not so much in oscillation as in emis- 

 sion. In electrolysis the emitted substance is 

 matter; in Rontgen rays it is ether; and cathode 

 and other rays seem to be intermediate forms, 

 lonization is a subatomic, not an atomic, phe- 

 nomenon. H. Becquerel (Comptes Rendus, Dec. 

 9, 1901) has prepared by successive fractionations 

 two varieties of uranium salts, one of which is 

 more radio-active than uranium itself, while the 

 other is almost inactive. After eighteen months 

 the progressively enfeebled products thus pre- 

 pared were found to be almost identical, and 

 had regained their activity. On the other hand, 

 the abnormally active salt was found to have be- 

 come completely inactive. The author suggests 

 that the deviable rays, identical with the cathode 

 rays, are the cause of the emission of the non- 

 deviable radiation, which would then be analogous 

 to the Rontgen rays, this spontaneous emission 

 being comparable with the evaporation from an 

 odoriferous body. The energy would be fur- 

 nished by the active body, but the loss of weight 

 would be too feeble to be observed. There would 

 be two kinds of particles, one about 1,000 times 

 smaller than the other; on separating, the smaller 

 would carry negative charges, and would attain 

 such enormous velocities that they could pass 

 through solids, while the larger ones would move 

 more slowly, and behave somewhat like a gas, 

 forming on all bodies, excepting those electrified 

 positively, a material deposit, which would be 

 capable of dividing itself in its turn into smaller 

 particles. This would explain induced radio-ac- 

 tivity, and it would be in consequence of this mo- 

 lecular subdivision that induced radio-activity 

 would dissipate itself, even across an envelope of 

 glass. The emanation which produces radio-ac- 

 tivity must not, however, be considered as similar 

 to an ordinary gas, for Curie has shown that 

 equilibrium between active matter and the in- 

 duced walls of an enclosure in which it is confined 

 is a function of the quantity of active matter. 

 There is thus no phenomenon analogous to the 

 maximum tension of a vapor. Elster and Geitel 

 (Physikalische Zeitschrift, July 6, 1901) believe 

 that ordinary air contains a radio-active gas, 

 since, in the presence of a negative charge, it 

 makes other substances upon which it impinges 

 radio-active. Certain anomalies in electrical dis- 



persion in closed rooms, when bodies are intro- 

 duced which have been long exposed to electrified 

 air, are explained by them on the supposition that 

 natural atmospheric air in contact with nega- 

 tively charged bodies of any kind makes these 

 bodies radio-active. P. Curie and A. Debierne 

 (Comptes Rendus, Dec.' 2, 1901) find that various 

 solid bodies acquire induced radio-activity when 

 placed in a closed vessel with a radio-active salt 

 of radium, preferably in the form of an aqueous 

 solution. This induced activity is independent 

 of the pressure, and of the nature of the adjacent 

 gas. Substances that become phosphorescent on 

 exposure to light, and a few others, become lu- 

 minous when placed in an activating enclosure. 

 If a solution of an active barium salt containing 

 a few milligrams of radium be put into a glass 



tlobe, and in another communicating with the 

 rst by a bent tube a substance such as sulfid 

 of zinc, the latter becomes as brightly luminous 

 as when it has just been exposed to intense light. 

 This is due to the induced radio-activity commu- 

 nicated through the bent tube. This induced 

 radio-activity of bodies placed in an enclosure de- 

 pends essentially on the free space existing 

 around them. An activating enclosure of glass 

 is illuminated throughout, although not equally, 

 the maximum of both light and activity being 

 in the wider portions. E. Rutherford (American 

 Physical Society Bulletin 2, 1901) finds that the 

 excited radio-activity produced by thorium com- 

 pounds is intimately connected with the power of 

 giving off a radio-active emanation. The emana- 

 tions from thorium and radium behave like 

 radio active gases or vapors, in that they diffuse 

 rapidly through gases and through porous sub- 

 stances like cardboard. The author considers 

 that these emanations are in some way the direct 

 cause of excited radio-activity. The character- 

 istic property of this form of radio-activity ia 

 that it can be confined to the cathode in a strong 

 electric field. Probably the radio-activity is due 

 to the transport in the electric field of positively 

 charged carriers of some kind. The author de- 

 scribes experiments that support this view and 

 shows that the carriers travel in an electric field 

 about as fast as the positive ion. F. Henning 

 (Annalen der Physik, March) imparted induced 

 radio-activity to various wires and metal plates, 

 and then measured their activity by their capac- 

 ity of producing conductivity in air. One of his 

 objects was to find the connection between the 

 intensity of activation and the area of surface of 

 the wires and plates. After the potential differ- 

 ence was raised to a certain value the inciva-e 

 of activity was small, though at first the activity 

 rose rapidly in intensity as the potential differ- 

 ence was increased. The activity appears to be 

 quite independent of the area of the surf aw with 

 high tensions, but with small potential differences 

 the intensity clearly increases with the surf are. 

 A condition of equilibrium appears to establish 

 itself in which the particles or corpuscles to 

 which the emanation is due disappear as rapidly 

 as new ones are produced. H. Geitel (Archive! 

 des Sciences, February) concludes from experi- 

 ment that any conductors placed in a large mass 

 of air, on being charged negatively, become cov- 

 ered with a superficial layer possessing tempo- 

 rary radio-activity. In natural caves and in a 

 large disused cellar the air showed a remarkable 

 conductivity in these circumstances. In air, 

 and in gases generally, ions may exist capable 

 of forming combinations with the negative elec- 

 trons at the surface of conductors, and this may 

 be the primary phenomenon of radio-activity. The 

 question arises if it is possible to combine the 



