102 NUCLEATION OF THE UNCONTAMINATED ATMOSPHERE. 



tion with clear northwest wind, while the following day (zyth) well 

 illustrates the effect of clouds and northeast wind. It is interesting to 

 note that the blizzard and snow produced no further diminution. On 

 the 2oth another midday minimum occurs, with a clear west wind all 

 day. The 2ist shows the rise due to clearing sky. 



IS. Remarks on the tables (brass fog chamber). The observations 

 were interrupted from the 22d to the 2gih on account of some needed 

 repairs, and after that date the brass trough replaced the wooden one 

 previously used. With the low nucleations frequently found, a fog 

 chamber rigorously free from leaks is essential. 



During January, maxima, usually accompanying clear weather and 

 west to north wind, occur on the 5th, loth, i6th, 23d, and 2yth to 

 28th ; minima due to rain or snow, with wind from the opposite 

 quarter, appear on the 3d, 6th, i2th. 22d, and 24th to 25th. On the 

 4th, the notched minimum is uncommon, for the weather at the sev- 

 eral times of observations is ^ ^ ^ "Q, . The 5th shows a 



high reading, as the wind passes through the northwest, and the nth 

 a sun and cloud effect. One may notice a curious gradual decrease 

 on the 1 6th, iyth, and i8th, with continual clear weather and westerly 

 wind. Clouds on the morning of the 2oth bring the maximum later 

 in the day, and the next day (2ist) shows an unusual maximum, with 

 cloudy sky and northeast wind. 



During January and February there is a noticeable tendency to a 

 uniform type of day curve, rising rather steeply from 9 o'clock until 

 noon or later, and falling more gradually during the afternoon and 

 evening. This is what one would expect on sunny days, in view of 

 the fact that nuclei seem to persist for some time in the atmosphere. 

 This curve is quite well shown on the lyth, iSth, and igth. 



In February the maxima are higher, and occur on the ist to 5th, 

 7th to 8th, loth to nth, I4th, :8th to igth, 23d to 25th, and 2yth to 

 28th. On the 6th, gth, i2th to i3th, and 2oth we have rain minima, 

 and low readings due to clouds on the i5th, iyth, and 26th. The 8th 

 shows an interesting minimum during a temporary shift of the wind 

 to northeast, and the I3th a depression during the rain in the middle 

 of the day. Clearing weather on the afternoon of the I5th brings a 

 rise of nucleation, which attains an unusual value next day. A quick 

 drop occurs on the 2ist when the wind changes to east, and the 

 opposite effect appears on the 26th. Another curious midday mini- 

 mum may be noticed on the 28th. Throughout the month the minima 

 are very quickly established by clear weather and northwest wind. 



