ATMOSPHERIC ELECTRICITY. 



331 



(1) In his observations on atmospheric electricity made during clear days of the month 

 of March, 1830, M. Arago found that the mean hour in respect to the first maximum was 

 about 8/2. 48m. for the same month. 



These observations show that the different periods of the year exert 

 a striking influence on the intensity of atmospheric electricity in clear 

 weather as indicated by the electrometer. This fact was previously 

 established by Cavallo,* who found the intensity with which it acted 

 greater in cold weather than in warm. Voltaf observed that in winter 

 his electrometer indicated from ten to twenty degrees as the maximum 

 of the morning, that it often indicated eight degrees towards the hour 

 of sunrise, while in summer the maximum of the morning rose to only 

 six degrees, and that of the evening to eight. De SaussureJ observed, 

 likewise, that atmospheric electricity is much weaker in summer than 

 in winter ; at the latter ])eriod of the year, in the open country, he 

 observed the small balls of his electrometer diverge two lines, whereas 

 in summer their greatest separation was but one line. This circum- 

 stance was especially to be noted in Schubler's§ observations, as 

 may be seen by the following table, which includes the mean intensi- 

 ties of the electricity of clear air at mean periods of the maodmoj and 

 minima, as well as the general mean and absolute 'maximum of each, 

 month. 



•"' Trait6 complet d'Electricite, pa.ge 293. 



f Dictionnaire de Gehler, tome VI, page •17.5. 



j Voyages dans les Alpes, tome II. § 803, page 225. 



§. Journal de Schwxigger, tome VIII, page 21. 



