130 NUCLEATION OF THE UNCONTAMINATED ATMOSPHERE. 



Mr. Pierce has compiled the following summary of monthly averages 

 of vapor pressure, temperature, barometer, sunshine, rainfall, etc. 

 Of these the data for temperature and precipitation are most important. 

 The latter was, in fact, a minimum (0.05) in February, but differing in 

 value but slightly from November (0.06) and March (0.07). It is not 

 probable that any effect was thus produced. Similarly the tempera- 

 ture is a minimum in February (25), differing, however, by but 3 

 from January (28), while the nucleation is more than doubled 

 (14/5.4). Moreover, the December maximum of nucleation does not 

 exist for temperature. It seems, therefore, equally improbable that 

 for so small a difference of temperature, so enormous differences in 

 general combustion (if this were the cause) could be evoked, and more 

 likely that both the temperature minimum and the nucleation are 

 different effects of some other common cause. 



TABLE 63. Meteorological Data. 



There does not, therefore, seem to be in the weather conditions in 

 February any reason for so marked a change in the nucleation. 

 Neither is the temperature low enough nor the rains sufficiently infre- 

 quent to account for the accumulation of nucleation observed. 



These facts also appear in the ratios in table 62, showing that whereas 

 the Providence nucleation was 10 to 12 times larger in December and 

 January than the Block Island nucleations, the ratios fall off to but 5 

 in February, from which low datum they slowly recuperate. 



88. Conclusion. While the Block Island observations have there- 

 fore proved that much the greater part of the nucleations observed at 

 Providence is of local origin, it has not proved that all of it is of this 

 character. In fact, there remains a residue of 5 to 10 per cent of the 



