CHAPTER V. 



THE COTEMPORANEOUS NUCLEATIONS OF THE ATMOSPHERE 

 AT PROVIDENCE AND AT BLOCK ISLAND. 



83. Introductory. In the preceding chapter, Mr. R. Pierce, jr., has 

 given an account of his observations of the nucleation of the atmos- 

 phere at Block Island. I purpose in this place to give the corre- 

 sponding data for Providence. The two stations lie nearly enough 

 together to have about the same general meteorological elements, 

 while the conditions as to nucleation may be totally different. Block 

 Island is surrounded by a body of water the least radius of which, 

 measured from the center of the island, is nearly 20 kilometers. It 

 lies about 70 kilometers from Providence in a direction about 10 west 

 of south. Fully one-half of Block Island fronts the ocean, as is seen 

 in figure 94, Chapter IV. The atmosphere at the former place should 

 be relatively free from pollutions due to the habitation of man, while 

 the reverse is naturally true of the latter. It is unfortunate that in 

 both cases the prevailing winds are land winds, at least from a distance, 

 and in discussing observations it must be borne in mind that the wind 

 bearing is not indiscriminately in all directions. I shall at the same 

 time avail myself of the series of observations, extending over two 

 years, contained in my report* to the Smithsonian Institution, which, 

 with the present series, complete a three years' period. 



84. Observations. These are taken with less frequency than in the 

 former paper (loc. cit.), but are otherwise on the same plan. The 

 entries of the table are at once intelligible. The time of day is in hours 

 and tenths of an hour. Weather variations are noted from cloudy 

 (C), partly cloudy (FC) to fair (F). The temperature of the apparatus 

 is given in degrees Centigrade; those of the atmosphere in degrees 

 Fahrenheit. The coronal diameter, is shown under s, which is the 

 chord of a radius of 30 cm., when the eye at the goniometer and the 

 source of light are 85 cm. and 250 cm., respectively, from the fog 

 chamber. The number of nuclei per cubic centimeter, given under 

 n, has not been corrected for temperature, as the difference for the 

 present purposes is unessential. 



* Smithsonian Report, vol. xxxiv, 1905. 



in 



