574 



PHYSICS. PROGRESS OF, IN 1900. 



0.7099 X 10- 10 , which agrees remarkably well with 

 those found by experiment, such as that found by 

 Jager and Diesselhorst for aluminum (0.706 X 

 10- lu ). The author believes that the principles of 

 the kinetic theory of gases may be applied also to 

 liquids and to metals. 



Resistance. Lussana (Nuovo Cimento, August, 

 1899), in researches on the resistance of metals 

 and alloys when immersed in oil and subjected 

 to pressures up to 1,000 atmospheres, finds that 

 with increasing pressure the resistance diminishes, 

 tending to a minimum value at very high pres- 

 sures. If sufficient time elapse between the com- 

 pression and the measurement of the resistance 

 usually an hour the curves taken with increasing 

 and diminishing pressures are practically coinci- 

 dent. The coefficient is much smaller for the alloys 

 than for the pure metals. The author concludes 

 that the specific resistance of a metal depends not 

 only on the proximity of the molecules, but also 

 on their velocity of vibration. 



Vacuum Tubes. Wilson (Philosophical Maga- 

 zine, June) studies potential gradient in a vacuum 

 tube by means of a newly invented probe capable 

 of being shifted to any part of the discharge. The 

 discharge passes through a Torricellian vacuum, 

 and an open glass tube containing the two elec- 

 trodes floats on the mercury, whose surface can 

 be raised or lowered by means of an India-rubber 

 tube. Thus the vacuum tube proper floats up and 

 down in the vacuum, and through a slit in its side 

 the probes fixed into the side of the barometer 

 tube are capable of entering. Among other results, 

 the author finds a sudden drop of potential near 

 the anode, often amounting to as much as 35 volts. 

 He attributes it to the great rate at which positive 

 ions are shot off from the anode. Phillips (Elec- 

 trician, Sept. 29, 1899) finds that when the elec- 

 trodes in an exhausted bulb are magnetized after 

 the passage of the discharge at suitable pressure, 

 the discharge being at the same time shut off, 

 rotating luminous rings appear in the bulb in 

 planes perpendicular to the axis. Kelvin (ibid., 

 Aug. 4) explains these by supposing that after the 

 current is shut off the space is filled for some time 

 with negatively electrified particles, remaining 

 scattered through the inclosure. Each of these 

 must, during the initiation of the magnetic field, 

 experience an electrostatic force proportional to its 

 distance from the axis of the field, and in a direc- 

 tion perpendicular to the axis. This is just what is 

 required to explain the rotating rings. Wien 

 ( Physikalische Zeitschrift, 1, 1899) has under- 

 taken an investigation to see whether the radiated 

 energy due to electric discharge in gases can be 

 measured by the difference between the electric 

 energy supplied to vacuum tubes and the heat 

 produced in the tubes. The results show that 

 within the limits of experimental error the elec- 

 trical and heat energy are equal. Ikmty (Journal 

 de Physique, January) agrees with Wiedemann 

 that a rarefied gas can not be regarded as a true 

 electrolyte. He finds that the apparent conductiv- 

 ity of a rarefied gas is related to its luminescence, 

 and is directly connected with a violent action that 

 follows dielectric equilibrium, as the rupture of a 

 stretched wire follows its elastic equilibrium when 

 the stretching force exceeds a certain limit. The 

 ether in a perfect vacuum possesses perfect dielec- 

 tric elasticity, but gaseous molecules introduce 

 weak points Into it. 



Cathode Rays. Starke (Annalen der Physik, 

 September) has attempted to measure the direct 

 force exerted by cathode rays when they strike on 

 light, movable bodies. The results of Riecke, who 

 estimates the force from the motion of a propeller- 

 -li;i|>ed cathode, would show an amount of energy 



surpassing the whole amount possessed by the 

 rays, and such estimates are therefore inadmissible. 

 The author used a fixed propeller-shaped cathode 

 from whose blades the rays impinged upon sus- 

 pended aluminum plates. The results were almost 

 entirely negative, except that a very powerful in- 

 fluence machine gave a deflection indicating that 

 the force to be measured is less than 10~* dynes. 



Rontgen Rays (see also Bci-querel Ran*, under 

 'LiGHT). Graetz (Annalen der Physik, April) be- 

 lieves that the rotations produced in vacuum tubes 

 under the action of cathode rays may not be 

 directly due to the impact of projected particles, 

 since they appear at low pressures before the 

 cathode rays, and they cease at exhaustions at 

 which these rays are still present. The author 

 has also discovered that light dielectric bodies, un- 

 der suitable conditions, rotate rapidly when ex- 

 posed to Rontgen rays. Small spheres, bells, and 

 vanes mounted on needle points in an electric field 

 traversed by Rontgen rays continue to rotate while 

 the rays continue, the direction depending upon 

 the initial tendency. The rotations are strictly 

 analogous to those described by Quincke in the 

 case of liquids, and are covered by Heydweiller's 

 theory. Trowbridge (American Journal of Science, 

 June) has succeeded in generating Rontgen rays 

 by means of a battery current, using 20,000 storage 

 cells with an electro-motive force of more than 

 40,000 volts. The advantage of this method is the 

 possibility of exactly regulating the current and 

 difference of potential necessary to excite the rays, 

 which is not possible with any other method. 

 Zeleny (Philosophical Transactions, Nov. 9) de- 

 termines the velocity of ions produced by 1 tout gen 

 rays by comparing it directly with that of a stream 

 of gas. In a field of one volt per centimetre the 

 following velocities in centimetres per second were 

 obtained : 



Campanile and Ciomme (Physikalische Zeit- 

 schrift, June 23) find that at all potentials the 

 discharge of a condenser is accelerated by X ra\~. 

 though they are more effective at lower potential-. 

 Blythswood and Marchant (Proceedings of the 

 [London] Royal Society, <>.">. IS!)!)) show that the 

 absorption of Rontgen rays produced by normal 

 aqueous solutions of metallic salts having the same 

 acid radical increases with increase of atomic 

 weight of the base. Wind (Wiedemann's Annalen. 

 August, 1899) denies that it follows from the low 

 wave lengths obtained from diffraction images that 

 the rays are really 3.000 times shorter than tho-e 

 of yellow light. Flo asserts that diffraction im- 

 ages like those obtained can also be produced Im- 

 proper vibrations of any frequency, even that of 

 ordinary light, if only these vibrations experience 

 quite irregular changes of phase, with intervals 

 between them corresponding to the frequencies re- 

 sulting from the diffraction phenomena. 



Dielectric*. More I Philosophical Maga/in' 

 August), in opposition to the results of Hontgcii 

 Quincke. and others, finds that no changes of 

 volume and length are observed when dielectric* 

 are placed in an electrostatic field. Bonty 

 (Comptes Rendus. Aug. 20 to Sept. 10) has nica- 

 nred the dielectric cohesion of ga-e- at variou- 

 pressures by observing the value of the uniforn 





