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III. — On some Nuclei of Cloudy Condensation. By John Aitken, F.R.S. 



(With a Plate.) 



(Read 3rd May, 1897.) 



I have to apologise for placing this communication before you in a somewhat 

 incomplete form. My work has been much interrupted in the past, and it will again 

 shortly be stopped for a considerable time. I have therefore decided to place before 

 vou the results so far as they are worked out. 



PART I. 

 Ions and Cloudy Condensation. 



Robert von Helmholtz published in 1887 the results of "Experiments with a 

 •Steam Jet." # This investigation was continued, and he and Professor Richarz joined 

 forces, and the result of their investigation will be found in the same journal for 1890, 

 under the title — "On the Influence of Chemical and Electrical Action on the Steam 

 Jet, and on the Dissociation of Gases, particularly of Oxygen." t 



Helmholtz seems to have begun his work under a wrong impression as to the 

 conclusions of other investigators. In the first of these papers, after describing some 

 results, he says they cannot be explained on the dust theory ; and after stating that 

 some observers had rejected the dust theory, he adds that " Aitken, on the other hand, 

 has attempted to explain everything by it." In the second of the papers referred to, 

 the authors say : "We hold that the earlier assertions that cloud is never formed without 

 dust is incorrect." I have great difficulty in understanding how these authors could 

 have made this mistake, because in my first paper it is distinctly stated that cloudy 

 condensation can take place without dust ; and a number of experiments are described 

 in which condensation takes place in the presence of the vapours of different substances, 

 such as sulphuric acid, hydrochloric acid, and a number of others, — the very substances 

 one of the authors uses to prove that condensation can take place without dust. I had 

 also shown, that if the supersaturation be great enough, that condensation can take place 

 without nuclei of any kind. 



In my first communication on the subject in 1881 I even went further, and said 

 that it was probable that sunshine might cause the formation of nuclei, and allow 

 cloudy condensation to take place where there was no dust. On this point I shall 

 have something further to say in this paper. 



* Weid. Ann,, xxxii. pp. 1-19, 1887. t Weid. Ann., xl. pp. 161-202, 1890. 



VOL. XXXIX. PART I. (NO. 3). D 



