NUCLEATION AT BLOCK ISLAND. IOI 



76. Observations. In the data as given in table 57, the first column 

 contains the date and daily average ; the second and third, the time in 

 twentieths of a day and hours ; the fourth shows the condition of wind 

 and weather, R denoting rain, Sn snow, H haze, S sun, F fair, Fc 

 or F' or C' partly cloudy, C cloudy. The fifth column shows the 

 temperature of the instrument in degrees Centigrade, and the sixth, 

 the temperature of the outside air in Fahrenheit degrees. Column 

 8 shows the aperture of the corona on the given goniometer ; 9, the 

 principal colors from the center outward ; 10 (from March 29), the 

 relative humidity and vapor pressure ; finally, the last column gives 

 the nucleation in thousands of nuclei per cubic centimeter. 



It will be noticed that the temperature of tbe air in the trough varies 

 considerably at times from 20 C., the temperature for which reduc- 

 tions were made. Each reading was later corrected and the results 

 thus obtained plotted, where the correction amounted to more than a 

 thousand. The corrections as a rule were not large, however, and 

 the original curve shows the relative values equally well. The chief 

 effect is a slight reduction of the maxima on cold days. 



In the plates of the next chapter (figs. 95-101) the individual obser- 

 vations are plotted with the weather and mean temperature, the 

 nucleation being given in thousands of nuclei per cubic centimeter. 

 The lower curve belongs to Block Island, the upper curve to Provi- 

 dence, as will there be specified. 



11. Remarks on the tables (wood fog chamber). With the beginning 

 of observations at the island, there is a marked drop from the high 

 readings taken in Providence, showing that a large part of the nuclea- 

 tion observed in the latter place is due to local effects. The same 

 variations with meteorological changes are, however, observed, per- 

 haps even more strikingly. Thus one may note the sudden rise in the 

 afternoon of November 27, when the sky cleared and the wind 

 changed to northwest. On the 3oth the rain of the preceding night 

 is followed by a minimum, which, owing to cloudy weather, lasts 

 several days. Snow from the east and south on December 5 cuts 

 down the nucleation, which rises again with the clear sky and north- 

 west wind of the 6th (note the midday minimum) and holds during the 

 two cloudy but dry days following. The clear weather and northwest 

 winds of the gth, nth, and i4th bring decided maxima, while minima 

 accompany the northeast wind and cloudiness of the ioth, and the 

 snow from the same quarter on the i2th and i3th. Midday minima 

 occur again on the isth and i6th ; the high reading late in the after- 

 noon of the 1 5th is unusual. The i6th shows the increase of nuclea- 



