536 



PHYSICS, PROGRESS OF, IN 1901. 



always gave increased temperatures, provided the 

 gap was large. Small spark gaps lowered the 

 temperature, the probable explanation being that 

 while they do not alter the course of the dis- 

 charge, a part of the energy is lost in the form of 

 heat. The author also finds that when a dis- 

 charge takes place in a Geissler tube the intro- 

 duction of a special coil causes a rise of tem- 

 perature at the positive end and a lowering of 

 temperature in the neighborhood of the cathode. 

 H. Ebert (Archives des Sciences, August) has 

 measured the number of free ions in the atmos- 

 phere by drawing air through a tube connected 

 with an electrometer and screened by a larger 

 concentric tube. The electrometer remained 

 charged for several days after stopping the air 

 current. The number of free ions in the air seems 

 to increase with the purity and transparency of 

 the air and the intensity of the solar radiation; 

 both the number of free ions and their velocity 

 of discharge vary considerably. 



Rontgen Rays. L. Benoist (Comptes Rendus, 

 Feb. 11) finds that (1) the specific opacity of 

 a body for Rontgen rays is independent of its 

 physical state. (2) The opacity is independent 

 of the mode of atomic grouping e. g., of crystal- 

 line form, allotropic state, etc. (3) It is inde- 

 pendent of the state of liberty or combination of 

 the atoms. (4) In simple bodies, measured under 

 well-defined conditions, it is a . definite function 

 of their atomic weight and increases with the 

 latter. In the same publication (March 4) he 

 shows that transparency for Rontgen rays de- 

 pends on atomic weight in a large number of ele- 

 ments, and he even (ibid., March 25) infers the 

 atomic weight of an element from its transpar- 

 ency to the rays. Hebert and Reynaud (ibid., 

 Feb. 18) find that the absorption of the rays by 

 saline solutions is proportional to the atomic 

 weight of the metal in the salt. Sagnac (Annales 

 de Chimie et de Physique, March) concludes that 

 Rontgen rays travel in straight lines, subject to 

 scattering which bears no relation to the diffu- 

 sion or reflexion of light on the surface of the 

 body traversed. The peculiarities in the recti- 

 linear propagation of the rays are only appar- 

 ent, and the course of the rays is the same as 

 that of light rays. At the same time there is no 

 diffraction, refraction, reflection, or regular polari- 

 zation. All this is brought into harmony by the 

 theory of Stokes and J. J. Thomson, with the ad- 

 ditional observation that, with ordinary light, 

 refraction would be impossible if the wave-lengths 

 were less than twice the distance between the par- 

 ticles of the prism. It is also impossible where 

 the train of disturbance of the ether produced by 

 molecule impacts (Stokes) dies out in less than 

 twice the same distance. This result is the same 

 for transverse and longitudinal ether disturbance. 

 W. Rollins (American Journal of Science, No- 

 vember, 1900), in a discussion of current opinions, 

 holds that strained ether is necessary for the pro- 

 duction of cathode rays, and that the cathode 

 stream is due to gas amalgamated with the cath- 

 ode and stops when this is exhausted. He asserts 

 that the theory of indivisible atoms is not now 

 admissible, nor is the idea that the particles 

 in the cathode stream are ultimate components, 

 for their spectrum is too familiar, too complex, 

 and not new. The author holds that Rontgen 

 rays are short ether waves due to impact and 

 heating of the impinging particles, which become 

 radiant centers and thus cool down. The trans- 

 parency of aluminum to Rontjjen radiation is ex- 

 plained on the theory that aluminum atoms and 

 cathode-stream subatoms are made up of ulti- 

 mate atoms proportional in number to the atomic 



weight, and themselves identical for all elements^ 

 and that there is ether between these. A plati- 

 num target faced with aluminum is not an effi- 

 cient reflector of Rontgen rays, and the author 

 thinks that the aluminum atom is a more open 

 structure than a platinum atom. C. H. Wind 

 (Physikalische Zeitschrift, Feb. 9) describes ex- 

 periments that he considers to be the only ones 

 which have given a positive proof of the diffrac- 

 tion of Rontgen rays. This proof he gives by 

 using a microscopic wedge-shaped slit and .ob- 

 serving the widening of the image near the apex. 

 A diagram given shows two bulbous enlarge- 

 ments, one much smaller than the other, the lat- 

 ter being nearer the apex. G. Sagnac (Annales 

 de Chimie et de Physique, June) discusses the 

 mechanism of discharge by Rontgen rays, taking 

 secondary and tertiary radiations through the 

 field into account. The result depends upon the 

 thickness of the metal, the volume of air, the 

 nature of the metal, the nature and the pressure 

 of the gas, the strength of the electric field, and 

 the form and area of the metallic surface. The 

 differences due to the nature of the metal may bo 

 due to differences in the secondary radiations 

 from the metals, which make the air more con- 

 ductive. While the bolometric energy of the sec- 

 ondary rays may be much less than that of the 

 Rontgen rays exciting them, the activity of the 

 former may enable us to detect otherwise unper- 

 ceivable Rontgen rays. The ultra-violet rays 

 studied up to 1900 only dissipated negative 

 charges, and had no effect upon gases, while sec- 

 ondary as well as Rontgen rays affect gases di- 

 rectly. Some peculiarities of the action of Ront- 

 gen and secondary rays are readily explained by 

 means of the velocities and energy of the electric 

 charges, liberated by the rays, under the influence 

 of the electric field; and in certain cases these 

 may present analogies to cathodic phenomena. 

 A. Nodon (Comptes Rendus, March 25) shows 

 that Rontgen rays may be produced directly in 

 air, and outside the Crookes vacuum, under the 

 simultaneous action of ultra-violet rays and of 

 an electric field. The rays are propagated along 

 the lines of electric force, and are not emitted in 

 other directions. They are more active when the 

 direction of the force lines is that of the propaga- 

 tion of the ultra-violet radiation. The activity of 

 the rays is a function (1) of the intensity of 

 the electric field; (2) of the intensity of the 

 ultra-violet radiation; (3) of the wave-length of 

 the latter; (4) of the nature of the substances 

 at whose surface they originate. The general 

 properties of the rays thus produced are identical 

 with those generated in the usual way by means 

 of Crookes tubes. 



Electric Convection. Lippmann, by applying 

 the principle of the conservation of energy to the 

 experiments of Rowland upon electric convection, 

 showed that, according to his view, changes of 

 magnetic induction ought to produce movements 

 of electrified bodies in the magnetic field. Cre- 

 mieu (Comptes Rendus, Oct.' 8, 1900) describes re- 

 searches made with a pivoted aluminum" disk, 

 separated into two parts by mica, and free to 

 turn in its own plane in a magnetic field. As this 

 apparatus did not move perceptibly the author 

 concludes that there is no displacement of a 

 charged body due to magnetic influences. This 

 investigator's failure to verify Rowland's classic 

 experiment showing the magnetic effect of electric 

 convection has caused much discussion. H. A. 

 Wilson (Philosophical Magazine, July) main- 

 tains that it is to be attributed rather to the 

 methods employed than to the non-existence of 

 the effect. H. Fender (ibid., August) has sue- 



