. Conduction of electricity through gases and radio-activity; a text-book with experiments . t was shown (§56), in studying Rontgen rays, thatif a beam of Rontgen rays passed between two parallel platesso as to produce uniform ionization between them and thesaturation current measured for different distances apart ofthe plates the current was proportional to the distance betweenthem. The same is true for the a rays from radio-active bodiesif the ionization is uniform. The absorption of the latter type of rays, however, produces inthis connection a similar resultto that described in the last pa
. Conduction of electricity through gases and radio-activity; a text-book with experiments . t was shown (§56), in studying Rontgen rays, thatif a beam of Rontgen rays passed between two parallel platesso as to produce uniform ionization between them and thesaturation current measured for different distances apart ofthe plates the current was proportional to the distance betweenthem. The same is true for the a rays from radio-active bodiesif the ionization is uniform. The absorption of the latter type of rays, however, produces inthis connection a similar resultto that described in the last para-graph. As the distance betweenthe plates increases the absorp-tion increases and consequentlythe ionization does not rise asquickly as it would if the rayscould penetrate the whole dis-tance without suffering any ab-sorption. If there were no ab-sorption the ionization wouldincrease in proportion to thedistance between the plates. Since the absorption is greaterat higher pressures this deviation from direct proportionalityis more marked at the higher pressures than at the lower Fig. 58. RELATION OF CURRENT TO DISTANCE BETWEEN PLATES 17 T This effect is well illustrated by a set of curves, which aredue to Rutherford, shown in Fig. 58. At the lower pressuresthe current is much more nearly proportional to the distancethan at the higher pressures. These effects may be verifiedexperimentally by use of the same apparatus used in theexperiments of the last paragraph. Keeping the pressurefixed, measure the current for different distances between theplates from 2 or 3 cm. downwards and plot a curve showingthe relation between current and distance between the similar curves for several different pressures. Repeatthese experiments also in different gases and reducing theobservations to the same scale compare them. If the /? rays are used as ionizers, since they are much morepenetrating than the a rays, the absorption will play a muchless important part and the cur
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