Signalling through space without wires : being a description of the work of Hertz & his successors . iolet portion of the light of the Aspark pssists the occurrence of the B spark. But it is interest-ing to note what Elster and Geitel have found (see Appendix IV.,Fig. 59), that if the B knobs were subjected to steady straininstead of to impulsive rush—, if they were connected to 10 SIGNALLING WITHOUT WIRES. the inner coats of the jars instead of the outer coatings—thatthen the effect of ultra-violet light on either spark-gap wouldexert a deterrent influence, so that the spark would probabl
Signalling through space without wires : being a description of the work of Hertz & his successors . iolet portion of the light of the Aspark pssists the occurrence of the B spark. But it is interest-ing to note what Elster and Geitel have found (see Appendix IV.,Fig. 59), that if the B knobs were subjected to steady straininstead of to impulsive rush—, if they were connected to 10 SIGNALLING WITHOUT WIRES. the inner coats of the jars instead of the outer coatings—thatthen the effect of ultra-violet light on either spark-gap wouldexert a deterrent influence, so that the spark would probablyoccur at the other, or non-illuminated gap. With the alteredconnections it is, of course, not feasible to illuminate one sparkby the light of the other; the sparks are then alternative, notsuccessive. Wiedemann and Ebert, and a number of experimenters, haverepeated and extended this discovery, proving that it is thecathode knob on which illumination takes effect; and Hall-wachs and Righi made the important observation, which Elsterand Geitel, Stoletow, Branly, and others have extended, that. Fia. 8.—Zinc Rod in Arc Light, protected by Glass Screen. The lensesare of quartz, but there is no need for any lenses in this experiment;leakage of electricity begins directly the glass plate is withdrawn. a freshly-polished zinc or other oxidisable surface, if chargednegatively, is gradually discharged by ultra-violet light. It is easy to fail in reproducing this experimental result ifthe right conditions are not satisfied ; but if they are it isabsurdly easy, and the thing might have been observed nearlya century ago. Zinc discharging Negative Electricity in Light; Gold Leaf Electroscope ; Glass and Quartz Panes ; Quartz a piece of zinc, clean it with emery paper, connect it toa go!4 leaf electroscope, and expose it to an arc lamp. (Fig. 8). WORK OF HERTZ LECTURE. 11 If charged positively nothing appears to happen, the action isvery slow; but a negative charge leaks awa
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