8 



VAPOR NUCLEI AND IONS. 



When the radium tube is attached to the glass end (about i cm. 

 thick), similar gradations are observed, but this time with the large 

 coronas near the radium tube. (See fig. 5.) The ratio of w-values is 

 now about 2 for the given distances. The law of variation is difficult to 

 obtain in any of these cases, but when the brass end is predominatingly 

 active, the reduction of w-values is nearly proportional to distance, if 

 the usual mean values of s be taken together with the special observa- 

 tions. 



140 



120 



100 



80 



60 



40\\ 



20 



H 



\ 



Jf. 



on 



8k. 



Rad. on 



brass 



end 



DISTRIBUTION WITHIN FOG 



\*A 



V ib 

 \ 



\ 



*?. 





^- *A 



SO 



>S\ 



<y v. 



Radium on side 



*D 



.v - 



\ 



FIG 



5 



26 



CHAMBER 



~'V 









/ 

 s 



9/ 





-0- 



s 



-o - ' 



5 

 Cj 



Radium i on glass end. Sp =26 ^ ( " l ' o 



> 



^ 



AO* 



*D 



m 







u 



30 



40 



50 



in 20 30 40 10 20 



Fig. 5. Density of ionization (N) within the fog chamber at different 

 distances (D) from the brass end. Table 2. 



In view of the action of the glass end when the radium is attached 

 to it, it seems possible that the glass, large thicknesses of which are 

 always penetrated and permeated obliquely by the radiation, may be 

 active in both cases, but special inquiry is needed here. The glass 

 cylinder was found to be thinner (about 0.15 cm.) near its equatorial 

 parts (T), and to increase in thickness towards both ends. If, how- 

 ever, the phenomena were due to thickness of glass the coronas should 

 be largest near the middle and taper down toward both ends of the fog 

 chamber. This is not the case, as the coronas for a symmetrical position 

 of the radium tube decrease regularly from the brass to the glass end 

 of the apparatus. 



If the radium tube is placed on the outside of the brass cap, one 

 cm. thick or more, there is the usual moderate reduction of nucleation 

 here, from ^ = 65 to ^ = 24 thousands (63 per cent); but the change of 

 diameter of coronas within is of the same kind, decreasing from the 

 brass to the glass end, as above. 



