. The London, Edinburgh and Dublin philosophical magazine and journal of science. the penetrating power of nickel radia-tion, and more penetrating constituents to a lesser portion of the beam too soft to excite iron radiationwould be absorbed only to a limited extent. For example,it will be seen that a constituent of the hardness of chromiumradiation, of which the absorption coefficient in aluminium is136, would be absorbed to a less extent by iron than that ofthe radiation from selenium, the absorption coefficient ofwhich in aluminium is only 18*9. On the Avhole, then, thebeam afte
. The London, Edinburgh and Dublin philosophical magazine and journal of science. the penetrating power of nickel radia-tion, and more penetrating constituents to a lesser portion of the beam too soft to excite iron radiationwould be absorbed only to a limited extent. For example,it will be seen that a constituent of the hardness of chromiumradiation, of which the absorption coefficient in aluminium is136, would be absorbed to a less extent by iron than that ofthe radiation from selenium, the absorption coefficient ofwhich in aluminium is only 18*9. On the Avhole, then, thebeam after passing through iron would be richer propor-tionately in these softer rays than before, but these latterare much more easily absorbed by aluminium than thosespecially absorbed by iron, and therefore we would expectthe beam to be softer to aluminium after passing throughiron than before. * Barlda & Sadler, Phil. Mag. May 1909, pp. 739-76 of Rontgen Rays in Transmission through Matter. GG5 This explanation of the phenomena is borne out by thefollowing experiments. Fig-. An electroscope E3 (fig. 2) was placed with its apertureparallel to the primary beam. A guide S was arranged sothat different substances could be placed in the path of thebeam entering E2. The secondary radiations excited in thesecould be measured by E3. The ionization in electroscope Ejserving as a standard. Strips of Ti, Cr, Fe, Cu, Zn were used as radiators. Theamounts by which the ionization in E3 was diminished whensheets of iron and aluminium respectively (absorbing thesame percentage of the primary) were put at S, were diminutions in the secondary radiation indicated whichconstituents of the primary were cut off by the iron andaluminium respectively. The results are tabulated below. Table VII. SecondaryEadiator. X/p for secondary radiation in Al. Per cent, bywhich Al in pri-mary (cutting off63 per cent.) cutsdown secondaryradiation. Per cent, bywhich Fo in pri-mary (cutting off62 8 per cen
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