80 Intelligence and Miscellaneous Articles. 



and iron wire and through tinfoil. No influence could be observed, 

 although in the way the experiments were arranged an alteration 

 in the resistance of ■£-$■ per cent, could easily have been observed. 



After this negative result I returned to radiation, and allowed 

 primary sparks of very various duration to strike across, while the 

 resistances to be investigated were at a distance of less than 50 cm. 

 To produce the sparks an induction-coil 25 cm. in length was used 

 worked by three accumulators, but more frequently an induction- 

 coil 60 cm. in length worked by ten accumulators (24 amperes). 



By means of a spark-resonator it was always ascertained that 

 the primary spark was an oscillating one. The followiDg resist- 

 ances we*e used : — Various gratings of tinfoil fastened on ebonite, 

 the thickness of the tinfoil being 0-05 mm. to 0*01 mm., and the 

 resistances 0-478 12, 3-15512, 11-31 12, 36-3112; a grating of thin 

 iron wire on an ebonite frame (5-504 12) ; a german-silver wire 

 (0*57812), and a strip of tinfoil (1-06812) : both these last were 

 resonant with the primary spark; secondary sparks could be 

 obtained between the wire or the strip. In none of these resist- 

 ances was any trace of a variation observed (to ^ per cent.). 



When the gratings were not fastened on the ebonite, but were 

 fixed in an ebonite frame, I observed the phenomena described by 

 Aschkinass, but only when the strips were very close to each 

 other. The variations in the resistances were often very con- 

 siderable. The resistance of a grating of 6*712 was 3-612 after 

 radiation by the primary spark ; by an agitation again 5-1 12, 

 after radiation 3-212. This grating was dipped in solidifying 

 paraffin; it then showed a resistance of 7*8512, which became 

 4*75 12 by radiation, and by shaking increased to 7*612. It was 

 necessary to agitate violently to get back to the original high 

 resistance. No change in resistance could be observed with 

 gratings having great spaces between the strips. In one grating 

 the 22 strips were 0*75 mm. in breadth and likewise 0*75 mm. 

 apart. The resistance 11*8512 was the same after radiation as 

 before. 



Hence, from these experiments, the amount of the varia- 

 tion depends on the position of the strips in reference to each 

 other. If these are close the primary spark may give rise to the 

 formation of one or more bridges between adjacent strips, as 

 Branly* assumes with metal filings, and Lodget in what he calls 

 " microphonic detectors." Although much remains to be explained 

 in the latter investigation, it appears to me indubitable that, as 

 Aschkinass also thinks possible, the phenomena with metal gratings 

 belong to the same category, and are not to be ascribed to some 

 unknown action. — Wiedemann's Annalen, No. 11, 1895. 



* Journal de Physique, p. 459 (1892) ; p. 273 (1895). 

 t The Work of Hertz, pp. 20-26. 



