produced by ft and y Rays at High Pressures. 183 



from the corresponding plate of air, the true gas effect must 

 be represented by a curve the ordinates of which are con- 

 siderably less than those of Oz. When the aluminium plates 

 are 1 cm. apart, it is probable that at 80 atmospheres not 

 more than 25 per cent, of the total ionization is due to 7 rays 

 producing ft rays in the gas, and that at atmospheric pressure 

 the effect is negligible. 



When the plates are 2 cm. apart (fig. 10), the apparent 

 absorption coefficient of the emergent ft rays is equal to 

 0*025 cm." 1 approximately, and under similar conditions the 

 absorption coefficient of the ft rays from Ur X = 0*025 cm. -1 . 

 Hence it would appear that the ft rays produced by 7 rays 

 are similar in penetrating power to the ft rays of UrX. The 

 high values obtained for the absorption coefficients in these 

 experiments are due to the obliquity of the paths of the rays, 

 and to the multiple reflexion taking place in the chamber. 



Summary. 



1. The apparent coefficient of absorption of the ft rays 

 from Ur X was found to be 0*04 cm. -1 air. By a special 

 arrangement this value could be reduced to 0*007 approxi- 

 mately. 



2. The " emergent ' : ft rays produced by 7 rays from 

 RaO have an absorption coefficient 0*046 cm. -1 air, and 

 the incident ft rays 0*056 cm. -1 air. The emergent 

 ft rays are similar in penetrating power to the ft rays of 

 UrX. 



3. The absorption coefficient of the ft rays of Ur X, and of 

 the emergent ft rays when the plates are 2 cm. apart, is 

 0*025 cm. -1 approximately. 



4. The ft rays appear to be independent of the material of 

 the plates, as other investigators have also shown. 



5. When the plates are 1 cm. apart the ionization due to 

 y rays in the gas is negligible at atmospheric pressure, and 

 is approximately 25 per cent, of the total ionization at 

 80 atmospheres. 



I wish to thank Prof. Rutherford for suggesting this 

 research, and for his advice during the course of these 

 experiments. 



