DISTRIBUTION WITHIN FOG CHAMBER. 



7 



instance, passing continuously from the high to the lower values. This 

 experiment throws light on the function of the walls in producing dis- 

 tributions in case of persistent nuclei. Obviously the effect of secondary 

 radiation decreases rapidly as the distance from the walls increases. The 

 nucleation within the fog chamber is probably largely due to this kind 

 of radiation. 



6. The same, continued. Miscellaneous tests. In the second part 

 of table 3, experiments with radium are resumed for comparison. The 

 gradation of number, decreasing from the brass end to the glass end, for 

 a symmetrical position of the radium tube at T, fig. i, is very marked, 

 as usual; while the case for radium at R, fig. i, again shows the largest 

 coronas at the end of the tube, the distribution being more nearly uni- 



TablE 3. Distribution of ions within glass fog chamber. Metallic (brass) cap at one 

 end, glass end opposite i cm. thick. Lines of sight io cm. (s l0 ) and 30 cm. (s^) 

 from brass end, 15 cm. and 35 cm. from glass end. X-rays acting from distance D. 



1 Large coronas near brass cap. Secondary radiation preponderating. 



form. Thereafter the radium was placed in positions S, T, S', on top, 

 successively, with the results for T graded about as usual. Radium at 

 5 still evokes gradation, but the coronas are even much smaller than 

 when the radium is placed on the thick glass end at R. When radium is 

 placed at S' near the glass end gradation is nearly absent, but the coronas 

 are again small. The results are therefore not as simple as was antici- 

 pated and do not admit of an explanation merely in terms of the glass 

 penetrated. 



