634 



PHYSICS, PROGRESS OF, IN 1898. 



Conductivity. Van Gulik (Wiedemann's " Anna- 

 len," September) finds by experiments on the con- 

 ductivity of powders, by means of minute terminals 

 under the microscope, that the influence of electric 

 radiation increases conductivity by promoting 

 mechanical contact (Lodge's view) and not by modi- 

 fying the surrounding dielectric (Branly's view). 

 Smithells, Dawson, and Wilson (London Royal 

 Society, Nov. 17) conclude from experiments that 

 the conductivity of vaporized salt is electrolytic, 

 but differs somewhat from that of electrolytic solu- 

 tions. Ohm's law is obeyed within limits. The 

 conductivities of salts depe'nd on the electro-positive 

 constituent, and on the negative also at high con- 

 centrations. That of the haloid salts as a group 

 differs from that of the oxysalts, the former in- 

 creasing with the increasing atomic weight of the 

 halogen, while that of the latter is approximately 

 uniform, approaching that of the hydrates. 



Thermoelectricity. Rubens (" Zeitschrift fur In- 

 strumentenkunde ") shows that the capabilities of 

 the thermopile (now generally replaced by other 

 devices for measuring small thermal changes) may 

 be increased by reducing the thermal capacity of 

 the couples. He uses fine wires of iron and " con- 

 stantan " (a nickel alloy). The thermoelectric 

 power of this couple is about half that of an anti- 

 mony-bismuth couple, but this is outweighed by the 

 gain in sensitiveness, due to decreased thermal 

 capacity. Perrot (Paris Academy of Sciences, 

 April 25) finds that the ratios for the electro-motive 

 forces for a bismuth-copper couple in the two posi- 

 tions of the bismuth crystal (parallel and perpen- 

 dicular to the principal axis) are between 2 and 2.4. 

 Stansfield (London Physical Society, March 25) con- 

 cludes that thermoelectrically there may be two 

 classes of metals : (1) Ordinary metals, for which 

 the curve representing the first differential of elec- 

 tro-motive force with respect to temperature is a 

 straight line ; and (2) the platinum metals, together 

 with a few, such as nickel and cobalt, for which the 

 curve of this differential multiplied by the absolute 

 temperature is a straight line. 



Contact Electricity. Christiansen (Wiedemann's 

 "Annalen," December, 1897) finds that the gas sur- 

 rounding a jet of zinc, lead, or tin amalgam in- 

 fluences its uninterrupted length, the breaking up 

 of the jet being retarded by air, oxygen, and sul- 

 phurous acid, owing to contact electrification. Dry 

 air and oxygen have no effect. 



Discharge. Edmondson (" Physical Review," VI, 

 2) finds that the curves that represent the relation 

 between potential difference and sparking distance 

 are in general approximately hyperbolas, which be- 

 come practically straight lines for sparks longer 

 than 3 millimetres. Moore (" American Journal of 

 Science," July) finds that the gaseous pressure in 

 the direction of discharge is greater than that in 

 either of the directions at right angles by an amount 

 depending on the velocity of the discharge stream. 

 Toepler (Wiedemann's " Annalen," jubilee volume) 

 has succeeded in obtaining a stratified discharge in 

 open air, recalling the stratified anode light, by 

 interposing in the path of the spark a semi- 

 conducting plate of slate, granite, or basalt, and 

 ballasting the discharge with a heavy water re- 

 sistance. F. Darwin (Cambridge [England] Phil- 

 osophical Society, May 16) concludes from experi- 

 ments on the figures produced on photographic 

 plates by electric discharges that these figures 

 are due chiefly to the light of the discharge, 

 the difference between the effects of positive and 

 negative discharges being due to the difference in 

 the form of the discharge. Buisson (Paris Academy 

 of Sciences, July 25) finds that the velocity of the 

 electrified particles during discharge under the 

 influence of ultra-violet light varies from 2fi to 135 



centimetres a second, according to the difference of 

 potential between the plates of the condenser. It 

 is independent of the intensity of the light. Ruth- 

 erford (Cambridge [England] Philosophical Society, 

 Feb. 7) believes that the theory of discharge that 

 attributes it to the disintegration of metallic par- 

 ticles will not explain the facts, and suggests that 

 gaseous ions are formed at the surface of the nega- 

 tively electrified plate. Heen (" Bulletin of the 

 Belgian Royal Academy") obtains by modifying 

 air with a Bunsen burner results in electro-dispersive 

 power which can not be accounted for on Villari's 

 theory of Rontgenized air, but indicate a special 

 kind of energy, named by the author infra-electric. 

 (For other discharge phenomena see the following 

 paragraph.) 



Propagation in Gases. Wiedemann and Schmidt 

 (Erlangen Medical Society) find that gases excited 

 to incandescence by electric discharges will absorb 

 electric waves even when they fail to do so if unex- 

 cited, but the dark cathode space will do so but 

 feebly. Their experiments also seem to disprove 

 the theory that conduction through rarefied gases 

 is electrolytic. Trowbridge (American Academy of 

 Arts and Sciences, XXXIII, 21) has installed a stor- 

 age battery of 10,000 cells, with which he has inves- 

 tigated the behavior of gases to discharges of very 

 high tension. He finds that beyond 1,000,000 

 volts the initial resistance of air decreases, and may 

 fall as low as 1.000 ohms between terminals 2 to 3 

 inches apart. X rays can be produced with an 

 electro-motive force of 10,000 volts, and there are 

 indications of them at 5,000. The behavior of rare- 

 fied media to powerful electric stress seems to re- 

 semble that of elastic solids to mechanical stress ; 

 a so-called vacuum, which acts as an insulator for 

 electro-motive forces that give a spark of 8 inches in 

 air (about 200,000 volts), breaks down under 3,000.- 

 000 volts. A single discharge with this voltage 

 through highly rarefied media produces X rays 

 powerful enough to photograph the bones of the 

 hand in one millionth of a second. During the 

 discharge the apparent resistance of the medium 

 is but a few ohms. The medium may be said to 

 lose its elasticity and be ruptured. 



Dielectrics. Gray (" Physical Review," Novem- 

 ber) reports from measurements of the dielectric 

 strength of insulating materials, made by himself 

 and his pupils, that in the case of air there is 

 practically no difference between the maximum 

 value of the alternating electro-motive force and 

 the static electro-motive force required to produce 

 a spark of given length in this medium when ap- 

 proximately flat plates are used as terminals. IE 

 the cases of some solids, as, for instance, paraffined 

 paper, the results seem to indicate considerably 

 greater strength against a static charge than against 

 an alternating electric stress, but the author con- 

 cludes that further experiments are desirable and 

 gives no results for such substances. Pellat and 

 Sacerdote (Paris Academy of Sciences. Oct. 1? 

 find that the dielectric constant of paraffin dimin- 

 ishes with rise of temperature, but that that ol 

 ebonite increases. Edmondson (" Physical Review. ' 

 VI, 2) finds that the dielectric strength of air ob- 

 tained with spheres is considerably higher than 

 that obtained by other investigators with planes. 



Vacuum-Tube and Cathode Phenomena. Trow- 

 bridge and Burbank ("Philosophical Magazine,' 

 February) have devised a tube in which the spaci 

 between anode and cathode is abolished and a con- 

 tinuous wire passes through the tube, which is thei 

 inserted in a circuit containing a spark gap and a 

 Trowbridge rheostatic machine, whose e<>mlensrr- 

 are charged in parallel and then discharged in 

 series, producing a voltage of nearly 1,000,(MM). Tht 

 tube glows all over and X rays' are developed, 



