056 



PHYSICS, PROGRESS OF, IN 1894. 



transmission of currents must be effected by the 

 intermittent contact of perfectly conductive par- 

 ticles. III. If we suppose that in a substance at 

 the absolute zero of temperature there is no rela- 

 tive motion among the molecules or among their 

 appreciable parts, it follows that every substance 

 at this temperature must have either infinite 

 specific resistance (which does not imply infinite 

 dielectric strength) or infinite conductivity." 



Convection. Hurmuzescu (Societe Franyaise 

 de Physique, reported in "Nature," Jan. 11) 

 finds that if dissymmetry be caused between the 

 2 knobs of a Wimshurst machine by fixing a 

 point to one of them, an electroscope placed at 

 some distance becomes charged when the ma- 

 chine is worked. The charge is higher when 

 the electroscope also has a point. That it is due 

 to convection, not to induction, is shown by the 

 fact that a metallic screen does not prevent it, 

 whereas an insulating shade placed over the 

 electroscope does. 



Discharge. N. Piltchikoff (Paris Academy of 

 Science) has devised a new method of studying 

 electric discharges. One pole of a Voss machine 

 is joined to a metal point, which is held over a 

 copper dish connected to the other pole and con- 

 taining a layer of castor oil. If the point is 

 positively charged a depression is formed in the 

 oil, and if a small screen is placed between the 

 point and the oil there is produced in the center 

 of the depression an elevation having the same 

 size and shape as the shadow of the screen would 

 have if the point were luminous. The phenom- 

 ena are shown even when a powerful air blast is 

 sent between the point and the oil. 



Electro-magnetic Radiation and Oscillation. 

 Mascart (" Comptes Rendus," No. 0) has meas- 

 ured the velocity of propagation of Hertzian 

 waves by calculating the period from the dimen- 

 sions of the resonator and from experimental 

 measurement of the wave length, using the data 

 previously obtained by Blondlot, from which the 

 latter thought he had shown a diminution of 

 velocity with increase of wave length. A more 

 accurate calculation of the frequency, made by 

 Mascart, gives a remarkably constant velocity, 

 whose mean is 303,200 kilometres per second. 

 This is about 1 per cent, higher than the veloci- 

 ty of light ; but Mascart thinks this due to the 

 fact that the calculated value of the self-induction 

 is too small. Birkeland and Sarasin (" Comptes 

 Rendus," Nov. 6, 1893) find that when electric 

 waves passing along a metal wire reach the end, 

 that part of the tube of electric force nearest the 

 wire turns about t he end almost immediately ; but 

 the distant parts, not being capable of the same 

 angular velocity, remain behind, and the tube 

 therefore curves like a comet's tail. As the ele- 

 ments of the tube continue to move at right an- 

 gles to their direction for the time being, the en- 

 ergy escapes from the end of the wire and is lost 

 in the surrounding space. P. Lebedew (Wie- 

 demann's " Annalen," August) has studied the 

 mechanical effects of Ilert/ian waves on resona- 

 tors at rest, and finds that when tuned to a 

 higher pitch a suspended resonator, whether re- 

 sponding to the magnetic or to the electric com- 

 ponents of the wave, is attracted ; when tuned to 

 a lower pitch it is repelled, the maximum effect 

 occurring near perfect resonance. F. Sanford 

 (" Physical Review," July-August) has succeeded 



in photographing by electric vibrations by lay- 

 ing a coin on the sensitized side of a plate and 

 connecting it with the terminal of a small in- 

 duction coil, while a piece of tinfoil on the op- 

 posite side, was connected with the other termi- 

 nal. Prof. F. J. Smith by the same method, but 

 using a higher potential, has obtained the same 

 results in one second, while Prof. Sanford re- 

 quired from a half hour to an hour. Garbasso 

 (Turin Academy of Science) finds that the elec- 

 tro-magnetic radiation reflected from a wooden 

 plank, though of large wave length compared 

 with the dimensions of the reflector, is not scat- 

 tered, but reflected regularly. Zehnder (Wie- 

 demann's " Annalen," November) has polarized 

 Hertzian rays elliptic-ally and circularly by means 

 of 2 wire gratings. Preece ("Engineering," 

 London, Feb. 23) has made noteworthy experi- 

 ments in inductive telegraphy. He has commu- 

 nicated across 3 miles of water by means of pow- 

 erful alternating currents sent through a gutta- 

 percha cable 600 yards long on the mainland 

 and 2 wires parallel to it on a distant island. He 

 also telephoned by induction across Loch Ness, 

 Scotland, 1^ mile. H. Poincare (Paris Academy 

 of Science, Dec. 26, 1893) has shown mathemat- 

 ically that when an electrical disturbance moves 

 along a wire, the head of the disturbance moves 

 with such velocity that in front of the head the 

 disturbance is nil, as in the case of light and of 

 plane sound waves : but the electrical disturb- 

 ance, unlike the others, leaves behind it a residue 

 of finite magnitude. Kenelly ("Electrical Re- 

 view," London, Dec. 15) finds that wires through 

 which oscillatory discharges have passed are cu- 

 riously bent sometimes at a right angle, and that 

 some show microscopic holes or craters. These 

 effects may be due to sudden expansion by heat- 

 ing. They are not influenced by a magnetic 

 field. Platin indium gives the best results. C. 

 E. St. John ("American Journal of Science." 

 October) finds that under very rapid electric 

 oscillations the self-induction of iron wires is 

 greater than copper, the difference varying from 

 3-4 to 4'3 per cent., and increasing as the diame- 

 ter decreases. Prof. John Trow bridge, of Har- 

 vard (" Philosophical Magazine," August), finds 

 that a unidirectional spark always excites an os- 

 cillatory discharge in a secondary circuit if its 

 self-induction, capacity, and resistance permit. 



Thermoelectricity. W. H. Steele, of Melbourne 

 University (" Science." No. 562), in experiments 

 on thermo currents in a single metal due to va- 

 riations in temper, found that a sensitive gal- 

 vanometer in circuit with a piece of iron wire 

 showed a current when the wire was simply 

 warmed with the fingers, but iron was the only 

 metal that gave a current with a temperature 

 below 100 C. A like effect was noticed in 12 

 different metals and 4 alloys. Gold gave the 

 highest electro-motive force 0-5 volt ; lead, cop- 

 per, tin, zinc, and antimony gave 0'3 volt : while 

 the highest effect obtained from iron was 0-002 

 volt. The phenomena seem to be sufficient to 

 mask ordinary thermoelectric effects at a red 

 heat, hence the accepted thermoelectric tables 

 are probably not trustworthy for high tempera- 

 tures. G. F. Emery (London Royal Society, 

 Feb. 8) has studied the thermoelectric properties 

 of salt solutions, and finds that in a circuit 

 formed by a metallic wire and a solution an 



