which enter the chamber, no matter what their direction, 

 proper correction being made for the effect produced by y 

 rays. 



By subtracting the readings taken with a screen at A 

 and at C a measure is obtained of the amount of radiation 

 which has been turned out of its original path or scattered 

 by that screen. Another reading with the screen at B en- 

 abled the distribution of the emergent scattered radiation 

 to be followed out. 



To obtain a measure of the returned, or incident, scat- 

 tered radiation the apparatus shown in fig. ii. was used. 



iToEartn. 



To Etecfromefcr. 



To3atf-eru. 



ToElecfrcmef&r. 



The top chamber. A, was the one already described, and 

 a similar hemispherical chamber, B, was placed as shown with 

 the Ra outside, contained in a Pb block provided with an 

 opening through which the )3 rays could pass, impinging on 

 screens placed in the position C . A stronger sample of Ra, 

 kindly lent by Dr. Hermann Laurence, was used in these 

 experiments, but care was taken to cover it with Cu foil, as 

 in the first set of experiments. Either of the electrodes A 

 or B could be connected to the electrometer, and as the 

 chambers were made as nearly as possible alike no appreci- 

 able change in capacity was introduced, using either chamber 

 separately. It was necessary to use a balance chamber, as 

 >2 



