552 



PHYSICS, PROGRESS OP, IN 1902. 



negative ions of the air with the positive electrons 

 of electrified conductors, but it has not been 

 found possible to obtain on positive conductors 

 layers analogous to those met with in negative 

 conductors. T. Tommasina (ibid., March) be- 

 lieves that the discharging action of the radio- 

 active substance can not be adequately explained 

 by ionization nor by emission of electrified par- 

 ticles. All the effects, he thinks, are to be traced 

 to anode radiation of the undulatory type. Thus 

 the flux from the anode arouses the cathode 

 rays, which, on striking a metallic plate, or the 

 glass walls of the tube, give rise to Rontgen rays; 

 these again excite further secondary rays, and so 

 on. All these radiations are complex, containing 

 parts deviable by the magnetic field, parts non- 

 deviable, rays of various penetrating powers, and 

 so on. The author describes experiments to show 

 that there are in the Becquerel radiation non- 

 luminous rays which discharge electrified bodies 

 and undergo reflection. 



Electricity. Theory. Kelvin (Philosophical 

 Magazine, March) proposes a modification of the 

 one-fluid theory, according to which the electric 

 fluid consists of minute equal and similar atoms, 

 which he calls electrions, smaller than the atoms 

 of ponderable matter, and capable of permeating 

 freely both the atoms and their interspaces. The 

 atoms are assumed to be spherical, and repulsion 

 is assumed between atoms and also between elec- 

 trions, with attraction between atoms and elec- 

 trions outside of them, both repulsions and at- 

 tractions being according to the law of inverse 

 squares. The attraction experienced by an elec- 

 trion entering an atom undergoes no abrupt 

 change, and decreases to zero simply as the dis- 

 tance from the center when the electrion is within 

 the boundary of the atom. Corresponding sup- 

 positions can not, however, be made for the force 

 between two overlapping atoms. The neutraliz- 

 ing quantum of electrions for any atom or group 

 of atoms has the same quantity of electricity 

 of one kind as the atom or group has of the 

 opposite kind. On these hypotheses many of the 

 phenomena of electricity are found to be capable 

 of adequate explanation. E. Carvallo (Comptes 

 Rendus, Jan. 20) claims to have discovered or 

 rediscovered for bodies at rest the following laws : 

 (1) The flux of the total electric current through 

 any closed surface is zero. (2) The line integral 

 of electromotive force round a closed curve is 

 zero. He discusses the electromotive force of 

 induction due to movement of matter, and says 

 that in the case of conductors and electrolytes 

 the force is equal to the velocity of matter, multi- 

 plied by the magnetic induction. M. Carvallo 

 also claims to have extended the two fundamental 

 equations established for bodies at rest to bodies 

 in motion, and to have given the electrodynamic 

 equations for bodies in motion. The equation of 

 energy he deals with as in ordinary mechanics. 



Contact Electricity. N. Hesenus (Russian 

 Journal of Physics and Chemistry, No. 1ft), by ex- 

 tensive experiments on metal disks, shows that a 

 polished surface is always positive toamat surface 

 of the same substance. This is equally true of 

 non-metallic bodies; for instance, a plate of wood 

 cut perpendicularly to the fibers will be negative 

 to one cut parallel to the fibers. The author 

 also shows that a metal will be more positive as 

 its hardness is less. Apparent exceptions to this 

 rule are easily explained, as by hygroscopic prop- 

 erties; for instance, a wet plate will be positive 

 to a dry one. Viscid substances, or substances 

 capable of giving off dust, will be positive to all 

 bodies, and dust will exhibit a negative poten- 

 tial-difference with respect to the body it is taken 



from, because its superficial density is less. The 

 well-known fact that two pieces of quartz when 

 struck together will shine in the dark is shown 

 to be due to the fact that both pieces carry a 

 positive electric charge, an almost invisible layer 

 of dust negatively charged being interposed be- 

 tween them. 



Conductivity. G. di Ciommo (Nuovo Cimento, 

 February) notes that the distinction between con- 

 ducting and non-conducting liquids is only a 

 matter of degree, for all liquids conduct to some 

 extent. He finds that the resistance in mixtures 

 can not be calculated from the respective per- 

 centages; it is generally less than would have 

 been expected, but the divergences vary. The 

 condition of the liquid becomes profoundly modi- 

 fied upon the mutual solution of two liquids. 

 H. A. Wilson (Philosophical Transactions, Nov. 

 22, 1901), from experiments to obtain informa- 

 tion on the variation of the conductivity of 

 air and of salt vapors with change of tem- 

 perature, concludes that Faraday's laws for the 

 passage of electricity through liquids apply also 

 to alkali salts in the state of vapor. This re- 

 sult supports the theory that the passage of 

 electricity through salt vapors is analogous to 

 the electrolysis of salt solutions. A.de Hemptinne 

 (Zeitschrift fur Physikalische Chemie, Dec. 13, 

 1901 ) has experimented on the conductivity of gase- 

 ous mixtures at the moment of explosion, using 

 two glass tubes, joined to a T, and a galvanom- 

 eter. The galvanometer is found to be notice- 

 ably deflected in mixtures of hydrogen and oxy- 

 gen when the presence of air and dust favor the 

 condensation of water vapor; the effect is much 

 weaker when the apparatus communicates with 

 a vacuum and when the experiments are made 

 at temperatures above 100 C. Hardly any de- 

 flection is observed in mixtures of hydrogen and 

 chlorine and of carbon monoxide and oxygen. The 

 author regards explosions as instantaneous 

 flames. 



Discharge Phenomena. G. A. Hemsalech 

 (Journal de Physique, February), analyzing the 

 work of Schuster and himself, concludes that an 

 electric spark is produced in the following man- 

 ner: The layer of air between the two electrodes 

 is first pierced by the initial discharge; then the 

 air near the path becomes incandescent: this is 

 the " luminous path." Immediately afterward 

 the space between the electrodes becomes filled 

 with metallic vapor produced by the initial dis- 

 charge; this is the "aureole." The oscillations 

 following the initial discharge traverse this 

 vapor and reheat it. Without self-induction the 

 discharge is abrupt and the energy is confined 

 chiefly to the initial discharge. K. R. Johnson 

 (Annalen der Physik, 5, 1, 1901), in a discus- 

 sion of the spark discharge, explains the pro- 

 duction of a mixture of hydrogen and ox\L r < n 

 at the electrodes of a water-cell placed in the 

 secondary circuit of an induction-cell as a re- 

 sult of oscillations set up at break. When (he 

 rise of potential at either electrode becomes great 

 enough, the electrode becomes coated with a la \vr 

 of gas, which stops the electric flow, and the dif- 

 ference of potential between electrode and elec- 

 trolyte becomes great enough to cause a spark. 

 The gas in the spark-gap is compared to a wall 

 on which an enclosed gas exerts a pressure, the 

 wall collapsing when the pressure reaches a cer- 

 tain value. The electric pressure required to 

 break down the dielectric is proportional to the 

 number of collisions on the wall that is, to the 

 frequency of the oscillations. A. Righi (Atti del 

 Lincei, May 4 and 31) finds that in a circuit con- 

 taining a rarefied air-tube with adjustable alu- 



