718 



PHYSICS, PROGRESS OF, IN 1890. 



power and conduction in various dielectrics, 

 especially in piezo-electric quartz. The conduc- 

 tivity of such quartz is strong in the direction 

 of the optic axis, and falls to zero at right angles 

 to it. Plates parallel to the axis, with the ex- 

 tremity of the axis connected to earth, behave, 

 at higher temperatures than 120 C. as dielec- 

 trics of zero-inductive power. With long heat- 

 ing the conductivity along the axis disappears. 

 He finds that water plays a capital role in the 

 conductivity of many dielectrics perhaps in 

 that of all. With plates of baked porcelain 

 kept moist, various types of conductivity can 

 be imitated. Herbert Tomlinson (London Physi- 

 cal Society, Nov. 15) finds that repeated heating 

 and cooling affects the electric resistance of iron, 

 the specific resistance being reduced, by heating 

 to 100 and cooling to 17 C., from 11-162 to 

 10-688 C. G. S. units. Afterward no further 

 change could be produced. B. 0. Peirce and R. 

 W. Willson (" American Journal of Science," 

 December, 1889) find that the resistance of a 

 cell when measured by alternating currents is 

 always smaller than that obtained by any other 

 method. This method "fatigues" all but the 

 so-called constant cells. In most cases the in- 

 ternal resistance decreases as the current deliv- 

 ered by the cell increases. Dr. Budde (Berlin 

 Physical Society, Feb. 7) finds that German-sil- 

 ver wires are unsuited for standard resistance 

 coils, for their resistance increases with time, as 

 they gradually become crystallized. An alloy of 

 copper and nickel gives the best results, becoming 

 absolutely constant after being heated to 100 C. 

 H. le Chatelier (Paris Academy of Sciences, 

 Feb. 10) describes the resistance curves of sev- 

 eral alloys. Those of ferro-manganese (13 per 

 cent, manganese) and platino-rhodium are regu- 

 lar, but both mild and hard steel have singular 

 points at 820 and 710. Silicon steel (3 per 

 cent, silicon) has only the point at 820. Ferro- 

 nickel (25 per cent, nickel) behaves very pecul- 

 iarly, and below 550 seems to exist in two modi- 

 fications. G. Vicentini and D. Omodei (Turin 

 Royal Academy. September, 1889) find that the 

 specific 1 resistance of mercury between and 

 850 C. can be represented by the formula 1 + 

 898-9 x 10- 6 t + 669-5 x 10~ 9 t' 2 + 101-8 x 10 -t s . 

 The specific resistance of the other metals at 

 their melting points is about proportional to 

 their atomic weights, bismuth and antimony ex- 

 cepted. Hugo Koller (Vienna "Berichte," ii, 

 98) has measured the resistances of various di- 

 electrics in mercury units with the following 

 results : 



Petroleum ether.. 2000xl0 1{ 

 Oil of turpentine.. 50 " 



Olive oil 100 " 



Bisulphide of car 

 bon.. 



Vaseline 2000 



203 



"Water 



Alcohol 



Ether 



Gutta-percha. 



Paraffin 



Hard glass . . 

 Soft glass 



lOxlO 7 

 200 " 

 200 " 

 100 " 

 100 " 

 100x103 



10 " 



Toluol . . 

 Xybl... 



Pure water is probably non-conductive, but if 

 it stands in glass it rises in conductivity from 

 day to day by dissolving the glass. (See also So- 

 lution.} Herr Pfeiffer (Wiedemann's "Annalen") 

 finds that water, if purified as thoroughly as 

 possible, when standing in Hir shows at first a 

 decrease in conductivity, which gradually gives 

 place to the normal decrease, and that this 



abnormal behavior is due to micro-organisms 

 which absorb the conducting substances in the 

 water. Carl Barus (" American Journal of 

 Science," September) shows that, in mercury, 

 and in concentrated solution of zinc sulphate, 

 isothermal compression decreases the resistance 

 nearly in proportion to the pressure ; and he 

 deduces from this the law that rise of temperature 

 causes decrease of specific resistance. 



Contact Electricity. J. Enright ("Philosophi- 

 cal Magazine," January), in investigating the 

 contact electricity of gases and liquids, concludes 

 that hydrogen holds its charge with amazing 

 tenacity and gives it up only when each molecule 

 individually comes into contact with a conduct- 

 ing body. Such contacts are difficult to effect, 

 there being no real contact even between a stream 

 of the gas and the liquid through which it bub- 

 bles. But when acid acts on zinc the nascent 

 gas comes into real contact with the liquid. By 

 connecting with an electrometer an insulated 

 vessel in which a chemical action is taking place 

 he says that he finds that such action produces 

 electrification. But Prof. 0. J. Lodge thinks all 

 Enright's results may be, and probably are, due 

 to the f rictional electrification of spray. Enright 

 had previously investigated the electric phenom- 

 ena of solution (London Physical Society, Nov. 

 1, 1889). No electricity is produced if nothing 

 leaves the vessel, but when gases escape the ves- 

 sel is charged positively or negatively, according 

 to the nature of the liquid. Zinc in hydrochloric 

 acid produces a deflection of the electrometer in 

 one direction while the liquid is acid, but this 

 decreases, and finally reverses when zinc chloride 

 is produced. The electrification appears always 

 to be positive when the gas leaves an acid, aiid 

 negative when it leaves a salt solution. 



Electrolysis. Prof. Planck (Berlin Physical 

 Society, Dec. 6, 1889) finds by mathematical 

 analysis that heat is the most important form of 

 energy in a dilute electrolytic solution. We may 

 assume that as a gas becomes warmer by com- 

 pression and colder by fall of pressure, so also 

 heat is developed in such a solution when the 

 ions increase in number, and disappears when 

 they are diminished per unit volume. Hence 

 the more diffusive processes in an electrolytic 

 solution whose composition is not uniform must 

 develop an " osmotic heat." 



Electrification of Steam. Shelford Bidwell 

 (London 'Physical Society, Dec. 6, 1889) finds 

 that the opacity of a jet of steam is increased by 

 bringing electrified points near it, and that its 

 color changes to orange-brown. There is little 

 or no absorption in the spectrum of anon-electri- 

 fied jet, but on electrification the violet disap- 

 pears and the bine and green diminish. Bid- 

 well concludes that electrification increases the 

 size of the water particles from something small 

 compared to the wave length of light, to about 

 Tnrrfuo- inch. Allied phenomena with a water jet 

 were observed by Lord Rayleigh, who found that 

 electrification made a straggling jet more co- 

 herent. This may explain the darkness of a 

 thunder cloud and the lurid light that accom- 

 panies it. Similar observations were made by 

 the late Robert llelmholtz. The sudden con- 

 densation is due perhaps to molecular tremors 

 or shocks, as when a supersaturated solution is 

 crystallized. 



