by Air of the Beta Bays from Radium C. 



13 



7 rays alone was determined. It has been shown by 

 Schmidt, and by Kovarik, that the value of fju is affected 

 by the material behind the radioactive source. The experi- 

 ments may be divided into two series : those in which there 

 was air, or carbon, or solid paraffin behind the radium tube, 

 and those in which lead plates were placed behind. The 

 values for fju in cm. -1 x 10 4 were : — 



Air behind 33,33,31. 



Carbon behind... 31. 



Paraffin behind... 35, 38. 

 Lead behind 37,37,40. 



As r increases from 60 to 140 cm. the value of jm is about 

 •0033 with air behind, and about '0038 with lead behind. 



In fig. 3 are shown graphically the results of two typical 

 series of experiments with air and with lead behind the tube 

 of radium. 



Fig:. 3. 



^ o cm 



30 



/zo 



/GO 



The " reflected " radiation from lead can be determined by 

 subtraction, and on multiplying by the square of the 



