G08 Mr. W. A. Borodowsky on Absorption of 



ft and y rays by different metals. The ionization current 

 in the electroscope was measured when screens of different 

 thickness were inserted between the radium and electroscope. 

 Thin screens of aluminium, copper, tin, and lead were used. 

 When the logarithms of the activity as ordinate were plotted 

 against the thickness of screens as abscissae, it was observed 

 that the curve after a rapid initial fall became nearly a 

 straight line parallel to the axis of abscissae. The point 

 where this line, when continued backward, cuts the axis of 

 ordinates was taken as the initial value of the 7 ray activity. 

 This value was found to be nearly the same for the curves 

 obtained with the different metals. The mean initial activity 

 of the 7 rays alone found from these experiments was 7 per 

 cent, of the total initial activiiy. 



When the empty glass cell or wedge was placed in its 

 position between the ft ray electroscope and the source of 

 radiation the emergent rays consisted of the same quantity of 

 7 ray?, but of a smaller quantity of ft rays. Consequently 

 the relative activity of the 7 rays was increased. 



The thin plates, of which the glass cells or the glass wedge 

 were made, absorbed a considerable fraction of the ft par- 

 ticles, and the value of the 7 ray activity was about 12 per 

 cent, of the total activity for the glass cells and about 15 per 

 cent, for the glass wedge. 



The constancy of the 7 rays over the range of experiments 

 was clearly shown by allowing the radiation to pass through 

 a sheet of lead 1*65 mm. thick covered by a glass wedge 

 with varying thicknesses of concentrated sulphuric acid, it 

 was found that the absorption of the 7 rays, even in the 

 thickest layer of acid, was too small to detect. 



The activity of the radium measured by the ionization in 

 the electroscope remained nearly constant over the whole 

 time of the experiments. There was a small variation from 

 day to day which was due to variations of barometric pressure 

 and temperature. 



All the readings of the aluminium leaf were taken between 

 the same points of the scale. The limits of error of several 

 readings did not exceed one per cent. The correction for 

 the small natural leak lay between "1 per cent, for the highest 

 observed activities and '6 per cent, for the lowest. 



The Relation between Absorption and the Chemical 

 and Physical State of Bodies. 



Two cells with thin glass bottoms were filled with different 

 liquids. One was placed in inverted position over the other 

 in such a manner that their edges exactly coincided, and the 



