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PHYSICAL NOTES 



Mk. J. E. H. Gordon has lately patented a method of pro- 

 ducing light from electricity based upon Mr. Spottisvvoode's 

 suggestion to apply the alternating-current magnetoelectric ma- 

 chine of De Meritens to the induction-coil. Mr. Gordon 

 arranges small balls of platinum or iridium, or of an alloy of 

 these metals, at the ends of fine platinum rods in pairs in the 

 middle of a suitable globe, and causes to pass between them a 

 rapid succession of sparks whereby they are raised to incand- 

 escence. There is no consumption of carbon or any other sub- 

 stance, and the lamps may be connected either in series or in 

 parallel branched arcs. The principal remaining disadvantage 

 is the noise attendant on the rapid sparks. A mechanical con- 

 trivance is added to bring the knobs near together when no 

 current is passing in the primary coil. The induction-coils used 

 are of comparatively small size. 



M. Terquem (Jour, de Phys., October) prepares, for the 

 receivers of air-pumps, brass plates with a circular groove, in 

 which is put a mastic fusing about 60°. The plate 15 placed 

 over a ves-el of heated water, and when the mastic is fu'ed the 

 receiver is brought down into the groove. When cool, the plate 

 adheres to the jar. These receivers are tubulated, and a 

 caoutchouc stopper in the tubule holds a tube bent at a right 

 angle and provided with a stopcock like those used by M. Carre 

 in his air-pump. For experiments witji the air-pump reveral 

 receivers with their plates can be easily prepared beforehand. 



M. LiPPMANN points out (Jour, de Phys., October) that fuU 

 justice has hardly been done to Carnot with reference to his law 

 (in thermodynamics). It seems to have been forgotten that he 

 verified the law directly by experiment ; and did not merely (as 

 is found stated in excellent treatises) furnish a demonstration 

 ct priori based on the indestructibility of heat. This is doubtless 

 due to the fact that Carnot's original work has long been 

 exhausted and unobtainable. M. Lippmann considers that work 

 a mine imperfectly explored. f 



E.XPERIMENTS have been made by M. Hesehus of the St 

 Petersburg Plrysical Society, as to the variations of volume and 

 coefiicient of elasticity of palladium and its alloys under the 

 influence of hydrogen absorbed. The alloys contained 25 per 

 cent, of gold, sih-er, and platinum. Wires 500mm. long and 

 0"4 mm. diameter served successively as cathode in electrolysis 

 of dilute sulphuric acid in a long vertical glass tube, where they 

 were stretched by weights so that their length could be measured 

 directly with a cathetometer. The alloy containing silver showed 

 the greatest increase of length, ir7mm. ; palladium-platinum 

 6' 14 mm. ; pure palladium 5 mm. ; and palladium-gold only o'g 

 mm. With a current of six bichromate elenients, the elongation, 

 very rapid at first, reached its maximum after nearly an hour. 

 The shortening after breaking the current proceeded in a similar 

 way, but less rapidly ; ct;. for palladium wire it was only 2'6 mm. 

 after twenty-four hours. Some experiments were made with the 

 aid of a recording apparatus, and they also proved that, con- 

 trarlly to Graham's opinion, the absorption of hydrogen takes 

 place more quickly than the reverse action, and even when 

 electrolytic oxygen is made to act on the wire (used as anode). 

 M. Hesehus made a special delicate apparatus for measuring 

 small variations in the length of wires. With this it was proved, 

 that during the first day the shortening of the wire charged with 

 hydrogen decreases very quickly, about the third day it becomes 

 constant ; it again decreases rapidly about the seventh day, then 

 approaches zero asymptotically. This agrees with MM. Troost 

 and Hautefeuille's experiments on the tension of hydrogen of 

 palladium. 



A PLU^■IO^IETER which registers the quantity of rain, and the 

 duration and hour of the fall, is described by S. Grimaldi in 

 Rivisla Scicnlifuo-Induslriak for October 15. 



Ix a recent note to the Vienna Academy, on the relation of 

 the daily and yearly variation of temperature to the eleven-years 

 sun-spot period, Ilerr Liznar first compares observations of the 

 daily variation at thirteen places (including St. Petersburg, 

 Calcutta, and Hobarton), and finds for all some correspondence 

 with the sun-spot curve. The curve from data for Vienna, 

 Prague, Caslan, Briinn, and Trieste from 1S57-70, brought to 

 an average, shows, for the minima of this \ariation in 1859-60 

 and in 1S70-71, a very good agreement with the corresponding 

 maxima of the sun-spot curve ; while the maximum of the varia- 



tion precedes the minimum of the spots by about two years. 

 With regard to the yearly variation of temperature, Dr. Hahn's 

 results for Leipzig are fully confirmed by data from eight other 

 places in Europe, tlie variation showing a maximum and minimum 

 corresponding to the maximum and minimum of spots. 



The combinations formed by phosphuretted hydrogen with 

 hydrobromic and hydriodic acids have been long known. Its 

 combination with hydrochloric acid has lately been effected by 

 M. Ogier (Jour, dc Phys., November) by compressing equal 

 volumes of the gases in M. Cailletet's apparatus. Compressing 

 about 20 atm. at -f 14°, small yellowish bright crystals appear, 

 and with sufficient pressure the two gases disappear entirely 

 (if the mixture have been well made), the tube being covered 

 with a crystalline coat w'ithout trace of liquid. If the upper 

 part of the tube be heated with tepid water (-r 20'"), the 

 compression produces a liquid layer. If the tube be slowly 

 cooled, and 60 or 70 atm. maintained, so as to get only a small 

 layer of liquid, the combination forms slowly in crystalline state. 

 Sudden compression, without external heating, will also produce 

 the liquid. On the other hand, if before there is any deposit ot 

 crystals the pressure be relaxed (from 25 atm. e.g.) one perceives 

 not a mist, but small, light, solid flocks, which slowly go down 

 the sides of the tube and disappear. The combination can also 

 be produced under cold without pressure ; crystals are formed 

 about - 30°. If the compound exist in the gaseous state, it is 

 almost wholly dissociated at ordinary temperature and pressure. 



An amplifying barometer has been invented by M. Debrun 

 {Jour, de Phys., November). Suppose a Fortin barometer, in 

 the tube of w-hich the mercury is kept at a constant height. 

 The cistern has two other vertical tubes open to the atmosphere, 

 one rising out of the mercury, the other from water over the 

 mercury. The variations of the water in the latter are read with 

 the aid of a scale, and they are thirteen and a half times greater 

 than those of the mercury in the other open tube. 



Recent experiments in capillarity by Herr Volkmann (Aim. 

 der Phys., No. 10) have led him to the following results:—!. 

 The influence (affirmed by Wilhelmj) of curvature of the w.aU 

 on constants of capillarity cannot be maintained, and is explicable 

 by the supposition of a faulty determination of specific gravity. 

 (The arrangement of the index is also objectionable.) 2. Ob- 

 servation of the height of rise between parallel plates warrants 

 the assumption of a constant wall-layer, on wdiich the liquid 

 rises. 3. The thickness of the wall-layer in the case of neat's- 

 foot oil and alcohol is found constant for plates and tubes at 

 o'co4 mm. 4. In so far as the results with neat's-foot oil and 

 alcohol may be extended to other wetting liquids, no influence of 

 curvature of the wall on constants of capillarity is demonstrable. 



Prof. Silow of Moscow has studied the magnetism of iron 

 chloride solution by the method of induced currents (Ann. der 

 Phys. No. 10), and finds that the coefiicient of magnetisation is 

 not a con-tant, but a function of the force of separation. As the 

 latter gradually increases, the former at first increases too, and 

 pretty quickly, but reaches a maximum and then decreases, first 

 quickly, then slowly. The liquid is therefore relegated to the 

 same class of magnetic bodies as iron, steel, or nickel, and the 

 author considers that probably all magnetic 'bodies show this 

 rising and sinking of the coefficient. 



In a paper which appears in the Ann. der Phys. (No. 10), 

 Herr Hankel gives the chief results of his study of the photo- 

 and thermo-electric properties of fluor-spar. He states, inter 

 alia, that the middles of the cube-faces become, in light, nega- 

 tive, the tension decreasing towards the edges, and especially the 

 angles, which often show the opposite polarity. It is the 

 chemical rays that act. The carbon electric light does better 

 than sunlight. Sparks between two Leyden jars give the eftects, 

 but the ligiit of Geissler tubes does not. Green Weardale crystals 

 were the most excitable (of the specimens tried). The intensity 

 of the effect generally grows witlr the depth of the colouring. 

 The tensions produced by light do not change to those of opposite 

 sign when the crystal is put and kept in the dark. Crystals long 

 exposed to light are weakened in excitability. A moderate 

 heatino- (to 130° to 150' C.) exalts the photoelectric effect. As 

 to theniioelectricity, rise of temperature produces tensions of the 

 same sign as illumination does. In cooling, the opposite elec- 

 tricities appear. In many crystals weakly excitable by light, 

 the thermoelectric tensions are greater than the photoelectric 

 (especially in the case of brown-red or brown-violet crystals). 



