CHAPTER V. 



THE COTEMPORANEOUS VARIATIONS OF THE NUCLEATION AND THE 

 IONIZATION OF THE ATMOSPHERE OF PROVIDENCE. 



By Lulu B. Joslin. 



85. Introduction. The results obtained by Professor Barus,* showing 

 a characteristic succession of the values of atmospheric nucleation 

 throughout the year, suggested a parallel inquiry into the variations of 

 the number of ions in the atmosphere in the lapse of time. The present 

 work was therefore undertaken at his instigation, and observations 

 systematically carried forward from August, 1905, to April, 1906. 



In addition to the main purpose in view, it was hoped that a number 

 of subsidiary questions might be answerable. Thus a large part of the 

 nucleation of Providence is of local origin and enters the atmosphere 

 with other products of combustion. Initially these nuclei were either 

 highly ionized themselves, or at least the atmosphere originally received 

 an accession of ions and nuclei in proportional quantities. It is therefore 

 of interest to inquire whether any of the ionization survives, or whether 

 there is any connection observable between corresponding changes of 

 the nucleation and the ionization of a given place. The results, which 

 are carefully tabulated in the present paper, seem to show that there is 

 no such connection whatever; or that the persistent ionization arises 

 from, and is maintained by, causes which are quite distinct from the 

 nucleation. No evidence has been found to suggest that the ionization 

 is either emitted or absorbed by the nucleation, whence it follows that 

 the ionization arises from causes wholly non-local. Apart from these 

 main purposes, the data are interesting as a continuous record of ion- 

 ization (which will be supplemented in the future), though, as yet, suffi- 

 cient time has not elapsed to ascertain whether the opposition in the 

 monthly positive and negative ionizations found in the sequel is real 

 or incidental. (Cf. fig. 62.) 



Finally, I may add that work to investigate a possible relation between 

 the nucleation and the ionization of the atmosphere was undertaken 

 in Helgoland and on the coast of the Ostsee by Prof. G. Ludelingf in 1902 

 and 1903, using Aitken's dust-counter. The time during which obser- 

 vations were recorded (August 21 to September 16, 1902, June 17 to 

 July 4, 1903) were insufficient to warrant general conclusions, however, 

 apart from the interesting special investigations which Professor Lude- 



* Smithsonian Contrib., xxxiv, No. 1625, chap, ix, 1906; Carnegie Institution pub- 

 lication No. 40, January, 1906, chaps, iv and v. 



f Two papers in the Veroffentl. Koniglich Preussischen Meteorologischen Instituts, 

 Berlin, 1904. 



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