. The London, Edinburgh and Dublin philosophical magazine and journal of science. high absorption in lead. Eve(Phys. Zeit. viii. p. 185, 1907) with a stronger preparationfound for X 4*1 over a similar range of lead. At 3 a sudden change to X = 27 took place and continued y-jRays of Thorium and 15] up to 5 7 mm., the limit of the measurements. We havebeen able to extend the range up to 25 cm. of lead, orincluding the 3 mm. thickness of lead as base to a totalthickness of 2*8 cm. Owing to the abnormally high absorption of the rays bylead, as noticed by G-odlewski, Disposi
. The London, Edinburgh and Dublin philosophical magazine and journal of science. high absorption in lead. Eve(Phys. Zeit. viii. p. 185, 1907) with a stronger preparationfound for X 4*1 over a similar range of lead. At 3 a sudden change to X = 27 took place and continued y-jRays of Thorium and 15] up to 5 7 mm., the limit of the measurements. We havebeen able to extend the range up to 25 cm. of lead, orincluding the 3 mm. thickness of lead as base to a totalthickness of 2*8 cm. Owing to the abnormally high absorption of the rays bylead, as noticed by G-odlewski, Disposition 1 could not beemployed, but Disposition 2 was possible. A new arrange-ment (Disposition 5) similar to Disposition 1 was used, inwhich the walls and base of the lead electroscope were 3 and the preparation was mounted 83 cm. absorbing lead and zinc were placed directly over thepreparation, and parallel experiments were done with radiumfor the same disposition. The results* for lead and zinc areplotted in the curves (fig. 3). The abscissae are centimetres. Rays of Actinium DENSITY OF LEAP of thickness multiplied by the relative density of the absorbercompared with that of lead. The aluminium curve wouldcoincident with that of zinc if plotted. The figure showshow abnormal lead is. Although the measurements weremade through a base of lead 3 mm. thick there is still thepoint of inflexion in the lead curve at 0*3 cm., noticed byEve, and a still more decided point of inflexion at 0*85 that the curve is linear up to 2*5 cms. For zinc andaluminium the curves are exponential. In Disposition 2 thecurves for copper, aluminium, and zinc are exponential after 152 Messrs. A. S. Russell and F. Soddy on the a small initial thickness (0*36 cm. for zinc), but for lead thecurve is convex to the axis up to 0*8 cm., as in Disposition 5,and then is straight. The results are tabulated below, theresults for lead referring to the straight part of the curvebeyond 0*8 cm.
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