ATMOSPHERIC NUCLEI. 



141 



90. Mean monthly nucleations. The data of table 48 suffice for the 

 determination of the average nucleations per month, care being taken to 

 omit the days on which no observations were taken. Table 50 contains 

 the results. 



These data are shown 

 in the lower graphs of 

 fig. 62. What is re- 

 markable is the gradual 

 rise of the curve to a 

 persistent maximum 

 reaching nearly into 

 April. True, the win- 

 ter was relatively mild 

 and the spring relatively 

 cold; but one would 

 not be prepared to pre- 

 dict nucleations so uni- 

 formly maintained be- 

 tween November and 

 April. The distribution 

 is in fact peculiar, as 

 may be seen by compar- 

 ing it with the nuclea- 

 tion of the preceding 

 years since 1902, in fig. 

 63. The uniformity of 



Negative 

 + ions 



Aug. sept. Oct. Nov. 



Dec. 



Jar 



Feb. Mar. 



Fig. 62. Average monthly ionization (thousands per 

 cubic centimeter), positive and negative as stated, 

 and nucleations (thousands per cubic centimeter), 

 observed between August, 1905, and March, 1906. 



the new curve, the absence of maxima in December, are striking. One 

 may note the upward march of the successive curves 1902-03, 1903-04, 

 1904-05. 



91. Measurement of ionization. To determine the number of ions in 

 the atmosphere, Ebert's* well-known apparatus was used. This consists 

 of a tubular condenser, the inner coat of which is charged and in con- 

 tact with a graduated electroscope. The air to be examined is passed 

 through the condenser by an aspirator-fan propelled by clockwork. 

 The air delivery of the machine is also carefully standardized. 



In order to test the same air which yielded the nuclei for the preceding 

 measurement, the electrical apparatus (E, fig. 576) was swung from the 

 outside of a window on a long swivel bracket (B). In this way it could be 

 drawn near the window for charging and examination with appropriate 



* H. Rbert: Illus. Aeronaut. Mittheilungen, October, 1902, pp. 1-10. 



