NUCLEATION CONSTANTS OF CORONAS. 75 



47. Conclusion. The new results lead to about the same conclusions 

 as the older data given above. The endeavor to obtain the negative and 

 positive steps of the ionization fails in my apparatus. Sometimes there 

 are suspicious breaks in the nucleation curve supporting such a tendency ; 

 but it is not sustained. 



What I always get is division of the totality of ions into two groups 

 a numerically small group with large nuclei, and a numerically large 

 group with relatively small nuclei containing all the ions. This occurs 

 even in such cases where I catch the vapor nuclei of dust-free air in 

 presence of the ions (radium at D = 4o cm.), and hence all ions, positive 

 and negative, must have been caught in an earlier stage of the exhaustion. 



The slopes of the air graph and the strong X-ray graph represent the 

 initial branches of a general law of distribution of molecular aggregates 

 such as is given by the theory of dissociation. They may therefore be 

 expected to be similar in their slopes, as they actually are. The results 

 therefore bear on the molecular structure of vapors. 



The question is finally to be asked why I catch the negative ions, etc., 

 at an apparently much lower supersaturation than C. T. R. Wilson. I 

 have entertained doubts whether the inertia of the piston in his appara- 

 tus is initially quite negligible; whether in any apparatus the computed 

 adiabatic temperatures were actually reached. Nobody has proved it, 

 and the case should be worst for small tubes. Moreover, in every appa- 

 ratus there must be a limit at which the smaller nuclei of a graded system 

 can no longer be caught in the presence of the larger nuclei. There is a 

 remote possibility that, whereas in the plug-cock fog chamber the exhaus- 

 tion starts rapidly but ends off with retardation, in Wilson's apparatus 

 it may start with relative slowness but finish with accelerated rapidity. 

 If the lower limits of condensation were due to emanations of metallic 

 or other material coming from the vessel, the effect should vary with 

 the intensity of the ionization, which it does not. If it were due to the 

 use of filtered air in place of stagnant air, as in Wilson's apparatus, it 

 should be equally evident with non-ionized air, where the limit of con- 

 densation agrees with Wilson's point for negative ions. 



The chief results of this section will be found in the charts, corre- 

 sponding points of which have been connected with straight lines with 

 no attempt at smoothing. In case of the air lines, results made at 

 long intervals of time apart have been summarized. 



