(3 Rays from Radium by Solutions and Liquids. GOT 



A round ring (fig. 1) with well polished edges was fastened 

 by means of Canada balsam or b} r means of water-gla-s to a 

 very thin cover-glass, which formed the bottom of the cell. 

 The area o£ the cells used was about 4 cm. 2 and the depth 

 between 2 and 3 mm. The area of the bottom of each cell 

 was accurately determined by measuring the diameter of the 

 rina, and the depth of the cell by weighing the cell filled 

 with mercury. 



The cell was completely filled with a liquid and a thin flat 

 cover-glass placed on the top, the excess of the liquid being- 

 withdrawn by means of filter paper. 



The mass of liquid was determined by weighing the cell 

 full and empty. The absorption of /3 rays by different 

 powders was also examined in the glass cells. The powdered 

 salt was put in a sifter and dropped into a glass cell through 

 fine muslin. The thickness of the powder was determined 

 from a knowledge of the weight and density of the salt. 



The glass wedge was constructed as follows (fig. 2). 

 vStrips of thin glass (140 x 40 X "2 mm.) were fastened along 

 their edges by suitable cement to accurately planed steel 

 plates (150 x 5 x 3 mm.) which were stiff enough to prevent 

 any bending when the wedge was filled with the liquid. 



Liquids with high surface tension would stay in the wedge 

 of their own accord, but those of low surface tension were 

 kept in by means of glass sides. At one end of the wedge 

 the glass plates (strips) were in contact, at the other end 

 they were kept apart by a piece of glass 2-3 mm. thick, but 

 in each case the thickness of the glass was determined exactly. 

 The parts of the wedge were held together by means of steel 

 clips at the ends of the steel plates. 



During the experiments the gl iss wedge filled with solution 

 was supported by a piece of wood with a scale on either side 

 so arranged that the zero mark corresponded with the centre 

 of the source of /3 rays ; thus the position of the wedge could 

 be read off directly from the scale, and the thickness of the 

 layer of the liquids over the centre of the source of /3 rays 

 could easily be calculated. The thickness of the liquid in 

 the wedge obviously increased in direct proportion with the 

 distance from the end at which the plates are in contact. 



The small ft ray electroscope used had a base 3x3 cm. 

 and a height 4 cm. It was provided with sulphur insulation 

 and with a leaf of thin aluminium foil in the usual manner. 



Method of Procedure. 



Preliminary experiments were made to find how far the 

 7 ray effect would interfere with the main experiments. 

 This question was settled by studying the absorption of the 



