44 



VAPOR NUCLEI AND IONS. 



41. The same, continued. X=ray bulb inclosed in lead. In the experi- 

 ments detailed the X-ray bulb was not inclosed, so that secondary 

 radiation issued from the whole surrounding environment. In the data 

 given in table 17 the bulb is surrounded by a wide lead box, containing a 

 window 7.5 cm. in diameter fronting the fog chamber. The window 

 was in a removable side or lid of the box. This was kept at a long 

 distance (D = 6oo cm.) in order to furnish weaker ionization than was 

 specified in table 15. 



20 25 30 35 40 



Fig. 24. Efficient nucleations in dust-free air, energized or not by radium or the X-rays 

 from different distances (D) and different exhaustions (dp). X-ray bulb not within 

 lead case, unless stated. 



In the first part of table 16 the exhaustion, dp = 27 cm., lies below the 

 fog limit of dust-free air. The low degree of ionization is thus shown 

 under different conditions. The second series contains a number of 

 successive exhaustions for an increasing dp, with the radiation passing 

 through a thin tin plate. Parts III and IV of the table are similar 



