Signalling through space without wires : being a description of the work of Hertz & his successors . Sometimes thetube is inverted, so that the active surface may be at D, further from theearth wire. Using the light from sparks admitted through a quartrwindow into the vacuum tube when a negatively-chargedamalgamated zinc surface was exposed near an earth-connectedplatinum ring, and between the poles of a small electro-magnet, they found that when the tube was full of air at 120 SIGNALLING WITHOUT WIRES. 10mm. pressure the magnet had but little effect, but that at0-15mm., whereas without the ma
Signalling through space without wires : being a description of the work of Hertz & his successors . Sometimes thetube is inverted, so that the active surface may be at D, further from theearth wire. Using the light from sparks admitted through a quartrwindow into the vacuum tube when a negatively-chargedamalgamated zinc surface was exposed near an earth-connectedplatinum ring, and between the poles of a small electro-magnet, they found that when the tube was full of air at 120 SIGNALLING WITHOUT WIRES. 10mm. pressure the magnet had but little effect, but that at0-15mm., whereas without the magnet the charge of -270 voltsdisappeared completely in five seconds, when the magnet wasexcited it only fell about half that amount in the same hydrogen at 0-24mm. the result was much the same, andat either greater or less pressure in both cases the magnet hadless effect. In oxygen the loss of charge was not quite sorapid; and, again, at a pressure of 0*lmm., the magnet morethan halved the rate. But in C02 the rapidity of loss wasextreme,* Either at 1-lmm. or at 0005mm. the charge of. To 13 6 Fig. 61. Explanation of Fig. 61.—P is the plae of amalgamated zinc, and R is theearth ring, as before. Ultra-violet light is introduced through a quartzwindow Q from a spark gap r. The vessel has a joint at the middle, sothat the sensitive plate can be got at and changed. Magnet poles areapplied outside this vessel in various positions. 270 volts leaked away completely in two seconds when themagnet was not excited ; but in the latter case (low pressure)exciting the magnet reduced the speed by about one-half. Atthe pressure of 1-lmm. the magnet did not seem toproduce an effect. With daylight the results are similar. * Corresponding to the activity of this gas as found by Wiedemann andEbert (Wied. Ann., XXXIII., p. 258), in their researches on the influenceof light on ease of sparking. PHOTO-ELECTRIC PHENOMENA. 121 The authors then discuss the meaning of the result, and it
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