634 



SCIENCE. 



[N. S. Vol. XVI. No. 407. 



fine in benzol, etc., I obtained results leading 

 to the same intei'isretation as those already 

 summarized for aqueous saline solutions in 

 my last article. The nucleus is to be regarded 

 as an exceedingly small droplet of concen- 

 trated solution, which persists, inasmuch as the 

 decreased vapor pressure due to solution, at a 

 certain specific radius, is exactly counter- 

 balanced by the increased vapor pressure due 

 to convexity. Thus, as my direct experiments 

 have long ago shown, the nucleus depends for 

 its size, cset. par. on the medium in which it 

 is produced or is generated; or in other words, 

 on the medium into which any emanation is 

 introduced or is generated. For if the nuclei 

 are solutions, then the critical density and 

 the diameter at which evaporation ceases for 

 a given nucleus will depend on the quantity 

 and kind of solute entrapped and on the vapor 

 pressure equation in the broadest sense (in- 

 volving temperature, surface tension, densi- 

 ties, etc.) of the given medium. 



If this is true, then it seems doubtful to my 

 mind whether the experiments of 0. T. R. 

 Wilson on the specific condensation effect of 

 ionization can further be regarded as crucial. 



3. If one introduces nuclei or makes nuclei 

 by aid of the X-rays, in what is virtually the 

 acid and the alkaline side of a battery, even 

 if the ionized moist air is the electrolyte, one 

 is surely conveying nuclei inter, or making 

 nuclei out of, different media. The stuif out 

 of which solutes are to be fashioned may be 

 available in different degrees on the two sides. 

 Whatever chemical effect is produced on one 

 side by the rays, need not at all be the same 

 as on the other side, any more than the effect 

 of shaking a very dilute solution need be the 

 same as the effect of shaking a stronger solu- 

 tion, where the results have been shown to be 

 enormously different as to the number, the 

 velocity and persistence of nuclei produced. 

 Hence from the accumulating evidence which 

 I have brought forward, I am led to infer that 

 the two species of nuclei in Wilson's experi- 

 ment are, for mere chemical reasons, liable to 

 be of different degrees of permanence, sizes 

 and numbers, quite apart from the electric cir- 

 cumstances involved. One cannot, therefore. 



afiirm that the difference (respectively posi- 

 tive and negative) of ionization is the imme- 

 diate and sole cause of the difference of pre- 

 cipitation rates specified, or briefiy that nega- 

 tive ions precipitate more effectively than 

 positive ions, because both a difference of 

 ionization and a chemical difference is in- 

 volved; and the right to assert that ionization 

 and not the chemical difference is the vera 

 causa may be called in question, when in every 

 other case the phenomena may be explained in 

 terms of the latter. 



I refer, of course, to immediate causes. 

 Eemotely, affinities and cohesions have the 

 well-known electrical relations; but with re- 

 mote causes I am not here concerned. 



4. Finally, if a marked difference in effi- 

 ciency as condensation nuclei of positive and 

 negative ions is granted, then any ionized 

 emanation, neutral as a whole, like that from 

 phosphorus, should produce two groups of 

 nuclei. On condensation there should be two 

 groups of coronal particles, interpenetrating 

 and subsiding through each other in the way 

 I have frequently witnessed in other experi- 

 ments. JSTo such effect has been observed. 

 Phosphorus nuclei are rather remarkable for 

 their identity, and the regular coronas ob- 

 served even after twenty-five or fifty exhaus- 

 tions. If there is any variation of size of 

 nucleus, it is graded as seen in the haziness of 

 planes of demarcation after long lapses of 

 time. 



5. While these conclusions as to the origin 

 of the different nuclei involve a theoretical 

 difference from Wilson's deductions, they are 

 not at variance with his practical conclusions; 

 for if, through any radiation agency two dif- 

 ferent emanations are generated (with oppo- 

 site charges or not), they would in a satu- 

 rated medium correspond to two different 

 nuclei, and the number of each kind and their 

 diffusion rates in general, would also be dif- 

 ferent. If they should, at the same time, be 

 opposed in ionization, a separation of charges 

 will result. Indeed if two or more groups of 

 ionized nuclei be generated in any manner 

 whatever, they are liable to have different 

 number and speed constants and lead to a 

 separation of charges, be it only by diffusion. 



