246 REPORTS ON INVESTIGATIONS AND PROJECTS. 



sity. One paper has been published correcting a fundamental theo- 

 retical error in a paper on the subject by Dr. H. A. Wilson, of Trinity 

 College, Cambridge. 



Barus, Carl, Brown University, Providence, Rhode Island. Grant 



No. 2 1 o. Investigation ofnucleation of the pure atmosphere . $ 1 ,000. 



The object primarily in view in this investigation was a continuous 

 record of the nucleatiou of the atmosphere in a locality relatively 

 free from the habitations of man, and therefore free from nuclea- 

 tions of local and artificial origin. This inquiry seemed well worth 

 while, after it had been shown that the nucleation of the atmosphere, 

 even above cities, obeys certain clear-cut laws, showing a marked 

 tendency to reach an enormously developed and sharp maximum in 

 December and a flat but very low minimum in June. Two series of 

 observations were made with similar apparatus simultaneously at 

 Providence and at Block Island. The two stations pass through 

 practically the same meteorological variations of wind and weather, 

 while Block Island is, in the winter at least, nearly free from local 

 effect. The data found at each station prove that the tendency to 

 pass through maxima in December, observed at Providence in 1902- 

 1903 and 1903-1904, has again unmistakably asserted itself. More- 

 over, the observations at both stations developed a new and surpris- 

 ingly pronounced maximum in February as the chief feature in the 

 nucleations of the last winter. Predominating in each of the series 

 of results over the earlier maximum, and holding for different bodies 

 of air, the February maximum at least can not be of local origin; 

 and it is thus in a measure probable that the December maximum 

 also is due to non-local causes. But whether these are the aggre- 

 gated effects of remote terrestrial sources, or whether they represent 

 an actual invasion of the atmosphere on the part of some cosmic 

 agency, remains to be seen. 



The air treated in the experiments was continually approaching a 

 state of purity so far as foreign admixtures are concerned. Hence 

 the properties of dust-free air, or in practice of filtered air, became 

 increasingly important. 



The method employed by the author for the study of dust-free 

 air is believed to be a new departure, inasmuch as all results are 

 expressed in terms of the number of nuclei observed per cubic centi- 

 meter, so that the nucleations produced are the criteria throughout. 

 To offer conditions sufficiently varied for the experimental work the 

 nucleation of dust-free air was coarsened by ionizing it, either by the 



