. Conduction of electricity through gases and radio-activity; a text-book with experiments . scale at different points. When a series of measurements are being taken with theelectrometer its sensitiveness should be tested at intervalsduring the measurements to ensure that it is not changing, JO RONTGEN RAYS or if it is changing to furnish a means of correcting for thechange and reducing all the readings to the same basis. The electrometer should be set up ready for use in themanner described in Chapter II in a convenient permanentposition near by the lead box containing the Rontgen ray bulb,so
. Conduction of electricity through gases and radio-activity; a text-book with experiments . scale at different points. When a series of measurements are being taken with theelectrometer its sensitiveness should be tested at intervalsduring the measurements to ensure that it is not changing, JO RONTGEN RAYS or if it is changing to furnish a means of correcting for thechange and reducing all the readings to the same basis. The electrometer should be set up ready for use in themanner described in Chapter II in a convenient permanentposition near by the lead box containing the Rontgen ray bulb,so that it may be connected to any apparatus set up in front ofthis box. 54. Production of Current Through the Air by RontgenRays.—Cut two plates of aluminium about 15 cm. square andset them up on edge on clean paraffin blocks so that they standvertical. Place these plates parallel to each other about 6 or 8cm. apart and 8 or 10 cm. in front of the window of the Ront-gen ray enclosure so that a beam of rays from the bulb 5 willpass between them as shown in Fig. 31. Over .the window place. EARTH EARTH EARTH Fig. 31. a thick lead screen with a rectangular hole cut in it about broad and 6 cm. high so that this hole is directly oppositethe center of the anode of the bulb. Arrange the plates P andQ symmetrically with regard to this opening. These dimen-sions are only given as a guide, but the exact width of the holeand the distance apart of the plates and their distance from thehole must be carefully arranged so that the cone of rays fromthe bulb will pass between the plates without touching theirsurface. This can be tested experimentally by holding the fluo-rescent screen just in front of the plates and noting the widthof the illumination on the screen which should be just a littleless than the distance between the plates. CONDUCTIVITY PRODUCED BY RONTGEN RAYS 71 To one plate P connect the positive pole A of a battery ofsmall accumulators of 20 or 30 volts, while the negativ
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