642 



PHYSICS, PROGRESS OF, IN 1892. 



found -000685. Lucas and Garret (" Philosoph- 

 ical Magazine," March) detect the spark in a 

 Hertz apparatus by causing it to ignite an ex- 

 plosive mixture of gases generated by electrol- 

 ysis. Arons and Rubens (Wiederaann's "An- 

 nalen," No. 10) by a bolometric method of meas- 

 uring electric waves find that Maxwell's law 

 connecting the dielectric constant with the in- 

 dex of refraction is very well satisfied. By it 

 the index () should equal the square root of the 

 constant (/x). The following are his experimen- 

 tal results : 



M. R. Blondlot (Paris Academy of Sciences, 

 Nov. 9) finds that between wave lengths of 8'94 

 and 35 g 36 metres electric waves have a velocity 

 of 297,600 kilometres per second. V. Bjerknes 

 (Wiedemann's " Annalen," No. 9) shows that the 

 so-called " multiple resonance" of Sarasin and 

 De la Rive ("Annual Cyclopaedia," 1890, p. 715) 

 may be explained mathematically as a phenom- 

 enon of damping in accord with the theories of 

 Hertz. Sarasin and De la Rive (Paris Academy 

 of Sciences, Sept. 19) have produced a spark by 

 a Hertz oscillator in liquid dielectrics. In olive 

 oil sparks of 1 centimetre in length were most 

 loud and brilliant. Prof. G. F. Fitzgerald 

 (London Physical Society, Jan. 22) has experi- 

 mented on the driving of an electro-magnetic 

 engine by electro-magnetic radiation. The 

 method that seems to promise most is one in 

 which collectors are joined to the ends of a vi- 

 brating circuit, and inductors and brushes are so 

 arranged that an insulating cylinder turning be- 

 tween them has positive and negative changes 

 distributed alternately on its periphery. By 

 suitable adjustment these could be so collected 

 as to keep up the vibration. Bedell and Crehore 

 ('' American Journal of Science," November) 

 show mathematically that when potential and 

 current are propagated in a conductor in har- 

 monic waves whose amplitude decreases with the 

 distance from the origin by logarithmic decre- 

 ment, the current wave is propagated in advance 

 of the potential wave. The wave of higher fre- 

 quency goes faster and decays most rapidly, the 

 phenomenon being most marked in the absence 

 of self-induction. Thus there is a limit to the 

 distance at which a telephone can be used, as 

 the components of a complex tone, as they ad- 

 vance, keep shifting their relative phases and 

 change their relative intensities. 



The Induction Coil. Tom Moll (Wiede- 

 mann's " Annalen," No. 2) finds by photography 

 that the duration of the spark from a coil is less 

 as the spark becomes longer, and greater as the 

 electrode is more pointed. In the latter case 

 the number of partial sparks increases, but the 

 mean interval between them is less. By rotat- 

 ing a disk of paper between the electrodes he 

 finds that the partial sparks are all in the same 



direction. He explains the discharge by assum- 

 ing that the electricity can not flow fast enough 

 to the electrodes, and that the partial sparks oc- 

 cur as soon as the difference of potential reaches 

 the necessary value. 



Glow and Vacuum Discharges. The electro- 

 static attraction experienced by a plane cathode 

 in a glow discharge has been found (Wiede- 

 mann s " Annalen," No. 1) to be measurable by 

 the balance, and to be proportional to the dens- 

 ity of the air. In negative glow there is an ex- 

 cess of free positive electricity proportional to 

 this density. The surface of the anode is more 

 feebly attracted and is less charged by reason of 

 this excess. The charge decreases with decrease 

 of pressure. It probably produces eddy currents, 

 which may account for the observed transfer of 

 matter in the positive direction. E. Goldstein 

 (Prussian Academy, vol. xl) concludes that the 

 term " stratification of the cathode " is a mis- 

 nomer, at least two of the strata pervading the 

 entire luminous region. He finds that the sec- 

 ond layer is emitted from the electrode nor- 

 mally to its surface, and is best shown by con- 

 cave poles. M. J. Pupin (" American Journal of 

 Science," April), in seeking to explain the solar 

 coronal phenomena, has studied the action of 

 vacuum-discharge streamers in the same bulb on 

 each other. He finds that they sometimes repel 

 where one would expect attraction. As stream- 

 ers in different bulbs do not affect each other, he 

 attributes the movements to a strain caused by 

 a distribution of gas pressure due to disturbance 

 of temperature, rather than to electrostatic ac- 

 tion. It increases with increased pressure. In 

 another paper (National Academy of Science, 

 April 27), Pupin states that his experiments 

 support Prof. J. J. Thomson's dissociation theory, 

 and indicate also a translationll movement of 

 the gas. An air blast introduced into the bulb 

 deflected the streamers. 



Dielectrics. E. Bouty (Paris Academy of Sci- 

 ences, June 13) has made a condenser whose di- 

 electric is an electrolyte by dipping two rigidly 

 connected iron disks in a fluid mixture of so- 

 dium and potassium nitrates which solidified 

 when the disks were withdrawn. The constant 

 k was found equal to about 4. Dr. W. L. Rohb 

 (" Philosophical Magazine," November) finds 

 that oscillations in the charge of a condenser 

 occur during the charging. Their amplitude 

 diminishes rapidly with the time, and may be 

 increased either by diminishing the resistance 

 or by increasing the E. M. F., self-induction, or 

 capacity. F. T. Trouton and W. E. Lilly (ibid., 

 June) measure specific inductive capacity by 

 the force with which a sheet of the dielectric is 

 drawn in between the plates of a condenser. 

 Prof. E. B. Rosa (ibid.. October), in experiments 

 on the specific inductive capacity of electro- 

 lytes, finds that for water and alcohol it has a 

 genuine value much greater than in other liquids. 

 His results are as follow : 



Water (at 16-5* C.) 70 



Alcohol (98 per cent )... 30" 9 

 Kther ... .8'4 



Turpentine 2-39 



Petroleum (300 test)... 2'04 

 Petroleum(illuminating) 1-97 



D. Negreano (Paris Academy of Sciences, Feb. 

 15), in experiments on benzene, toluene, and 

 xylene between 5 and 45 C., finds that the di- 

 electric constant diminishes with increase of 



