86 NUCLEATION OF THE UNCONTAMINATED ATMOSPHERE. 



nouncedly above it. The lead tube without radium is inactive. 

 Moreover, in the final part of the work all data are decidedly lower 

 than at first, as if the energizing quality were fatigued. This occurs 

 not only within the radium in lead tubes, sealed or not, but in the 

 case where the radium is in the sealed aluminum tube only. The air 

 values give evidence of an almost entire absence of nuclei. Reasons 

 for this unsatisfactory behavior can not even be conjectured. The mean 

 values given in thousands per cubic centimeter are : For air, N* 2.6; 

 radium in open lead tube, N-=22i2 ; radium in capped lead tube, 

 N=2i iS; air, N=2.2; lead tube without radium, N-=2.^ ; radium 

 in aluminum tube only, -A7==io; radium in open lead tube, N== 7 ; 

 radium in capped lead tube, N--="j ; air, N=o, remembering that the 

 radium is in all cases surrounded by the sealed thin aluminum tube. 



Apart from the fatigue it is clear that the open and capped tube 

 behave alike, proving that the rays actually penetrate the walls and 

 that secondary radiation is ineffective. This also follows from the 

 next paragraph, as the distance effect of radium is marked. The 

 amount of radiation passing 5 mm. of lead is here about 73 per cent, 

 but the present result is not as good as the above. 



TABLE 54. Penetration of 7-rays of radium. 5^ = 25 cm. Lead-cased fog chamber. 

 Radium in thin (o. i mm.) aluminum tube, hermetically sealed. Walls of each lead 

 tube 0.5 cm. thick. Plate, 0.14 cm. thick. Z? = 6-iocm. Lead tubes parallel 

 to walls of chamber, 20 cm. long. 



* Given in thousands per cubic centimeter. 



