. Conduction of electricity through gases and radio-activity; a text-book with experiments . the end of which is a metal circular frame ff 6 cm. indiameter, across which is stretched a fine copper grating con-sisting of very fine wires notmore than mm. in grating should be situatednot more than about a centi-meter from the quartz zinc electrode H, 5 cm. indiameter, is supported by a brassrod which passes out through anebonite plug, which in turn fitsinto a brass tube EF, solderedinto the end of the large cylinderand about cm. in diameter. This zinc plate may be a
. Conduction of electricity through gases and radio-activity; a text-book with experiments . the end of which is a metal circular frame ff 6 cm. indiameter, across which is stretched a fine copper grating con-sisting of very fine wires notmore than mm. in grating should be situatednot more than about a centi-meter from the quartz zinc electrode H, 5 cm. indiameter, is supported by a brassrod which passes out through anebonite plug, which in turn fitsinto a brass tube EF, solderedinto the end of the large cylinderand about cm. in diameter. This zinc plate may be adjustedanywhere from 5 to 10 mm. from the wire grating. Before be-ing placed in position this plate should be thoroughly cleanedwith emery paper so that it may present a bright, clean surfaceon which the ultra-violet light is to fall. All the joints betweenthe ebonite and metal, etc., are made gas-tight by waxing. Thewire grating is connected through the brass rod K to the elec-trometer while the zinc plate H is connected to the negativepole of the battery, the other pole being to IIO OTHER SOURCES OF IONIZATION Set up the spark apparatus so that the source of ultra-violetlight is at the principal focus of a convex lens of quartz, inorder to obtain a parallel beam of ultra-violet light after pass-ing through the lens. Allow this beam to pass into the ioniza-tion chamber through the window P and fall normally uponthe zinc electrode H. Start with the air in AB at atmospheric pressure. Run thespark a few times to secure regularity of action and thenmeasure the current produced between the plate and the gratingin the usual manner for different voltages on the plate H, andplot the usual voltage-current curve. Note that with even fairlyhigh voltages it does not reach perfect saturation. Reversethe potential, making H positive and test the current. Notethat in this case no current is produced, whereas if Rontgenrays were used an equal current would be produced. This indi-cates
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