A CONTINUOUS RECORD OF ATMOSPHERIC NUCLEATION. 



143 



November 29 is clearly associated with the drop in temperature, and there is 

 here one mid-day minimum but no others. 



Throughout December cold waves associated with northwesterly winds 

 are productive of maxima. After the rain of December i the nucleation rapidly 

 rises, accompanying a second drop in temperature. The maximum is moder- 

 ately sustained until the 3d, where there is fall into the rain minimum, partial 

 recuperation thereafter, and then another drop into the rain of the 5th. 



This rain soon changes into snow and from here the nucleation (chart 6) of 

 the cold wave begins, lasting from the 6th to the thaw on December n. One 



..6Jkc, 7 



17 18 



1<) XO 



CHART 6. 



may note the reduction due to very cold snow on December 7, and the curious 

 minimum accompanying the gale on the evening of December 8. The maxima 

 on the gth and loth accompany northerly winds and a drop in temperature. 

 The very remarkable maximum from December 13 to December 16 follows the 

 fall of temperature after the thaw on December 15, introducing a rain minimum. 

 This interesting region is no doubt referable to the snow-storm on the evening 

 of December 13, the winds remaining northerly. The ground was frozen on 

 December 13 and 14. The region is not due to temperature. The maxima on 

 December 17 and 20 are less sustained, but they come with temperatures above 

 freezing and westerly winds. The absence of night observations is a dilemma 

 in these cases. The low nucleation indicated on December 20 continued for 

 several days (December 20 to 23) beyond the limits of chart 6, but is shown on 

 chart 7. 



One may regard it as a general rule established by these charts, that the 

 nucleation increases when temperature suddenly decreases, but that tempera- 

 ture is not the sole or ultimate factor involved. To see whether this view 

 would work out in detail, I compared the observatory thermograph data for 

 Providence during the three months (kindly placed at my disposal by my 



