550 



NATURE 



{Sept. 19, 1878 



In the course of their experiments several curious and 

 interesting phenomena were noticed incidentally. A slip 

 of dry glazed note paper, when placed upon the disc of 

 the'discharger (Fig. 4), the other terminal being a point, 

 wa^ attracted to the disc so as to require a lateral pull 

 amounting, in some cases, to as much as 30,000 grains, 

 to cause it to slide over the disc : this lateral strain was 

 reproduced when the paper was pressed against the disc 

 by a weight of 129,690 grains. We must refer our 

 readers to the original memoir itself for the full discus- 

 sion of this phenomenon. 



When the terminals were placed opposite to two gas 



Fig. 16. — Repul>i:n of Gas-flame. 



jets emanating from the same gas pipe in metallic com- 

 munication with the gas main, and consequently to earth, 

 the flame opposed to the negative terminal is attracted, 

 but that opposed to the positive repelled, as was observed 

 to be the case with static electricity by M. Neyreneuf, at 

 whose request the experiment was made. Fig. 16 shows 

 the arrangement and effects observed. 



" When one of the terminals consisted of a very fine 

 platinum wire o'oo2 inch diameter and about o"56 inch 

 long, held in a holder like that used for holding needles 

 in a mathematical instrument box, but adapted to go into 

 the discharger, the M'ire took up a straight, circular, or 



elliptical oscillation, the glow at the point forming a con- 

 tinuous line of light marking its course ; with the point 

 positive the excursion was less than when negative, being 

 with a potential of 8,040 cells, and a distance between 

 the terminals of o'32 inch, about o"375 inch ; with the 

 point negative it was much more brilliant and about 

 o"8 inch. By interposing a resistance of^ 4 megohms 

 the statical discharge took place from the extremity of 

 the wire, frequently producing a beautiful and brilliant 

 figure by the apparent crossing and interlacing of the 

 bright lines of discharge from different points in the 

 path of the oscillating wire ; these occurred at such short 

 intervals that the discharge looked like a persistent pat- 

 tern of intricate engine-turning. By approaching the 

 wire cautiously it was generally possible to cause the end 

 of it to fuse into a minute globule, and the discharge 

 then became much more striking. With 4 megohms resist- 

 ance the static spark was longest and brightest when the 

 wire was negative ; if the wire was very straight, the 

 oscillations took place in a cycloidal curve in a vertical 

 plane, the discharge occurring at equal distances from 

 the middle of the path as the minute globule at the end 

 of the wire attained the limit of the greatest discharge 

 from either side, so that tvvo streaks of light were seen 

 continuously ; if the wire was slightly bent, the oscilla- 

 tion was conical or elliptical, and the figure produced by 

 the discharge was then much more continuous and beauti- 

 ful, because the distance from the point to the plate 

 remained nearly constant." 



Another point studied by the authors was the deflagra- 

 tion of wires of different metals. With their condenser 

 of 42'8 microfarads charged with 3,240 cells, they could 

 deflagrate 10*5 inches of platinum wire o"oi25 inch in 

 diameter. When 7.\ inches of either platinum, gold, silver, 

 copper, iron, zinc, or aluminium wire of this size, strained 

 across and kept in close contact with a piece of plate glass 

 perforated with two holes to admit of screw clamps to 

 press the ends of the wire tightly against it, is deflagrated 

 by the above charge, the wire is dispersed with a strong 

 explosion, like that of a pistol, the metal being driven into 

 and strongly adhering to the glass for some distance from 

 the wire. The greatest dispersion is towards the middle 

 of the wire, and all along the path of the discharge is 

 crossed by furrows in which the metal is deposited. This 

 appearance suggested the idea of a stress at right angles 



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Fig. 17. 



to the path of the discharge which might involve a notable 

 longitudinal contraction. 



An experiment was made to test this hypothesis, 

 Tjut the results were entirely negative. When the key 

 K (Fig. 17) was pressed down the accumulator c was 

 discharged through the wire w, which was 8 inches long, 

 and of diameters varying from o'2 to o"oi25 inch ; if now 

 the wire had, at the moment of discharge, contracted 

 longitudinally by xi^i5<5 inch, the fact would have been 

 recorded by the deflection of the galvanometer G, in 

 consequence of the closing of the circuit of the battery z, 

 at the extremity of the long arm of the lever ; with this 



apparatus, ho ..ever, the contraction, if it occurred, was 

 not detected ; the extremity of the lever was not observed 

 to rise before it descended in consequence of the elevated 

 temperature of w ; after w had been allowed to cool down 

 to its original temperature, the extremity of the lever 

 remained slightly below its original position. 



Only a few experiments have as yet been made by the 

 authors on the length of spark at different pressures below 

 that of the atmosphere, but they intend to pursue this 

 inrestigation with a micrometer discharger of longer range 

 than that shown in Fig. 4. 1 j- c 



With two spherical surfaces, each of 3 inches radius of 



