ATMOSPHERIC ELECTRICITY. 



327 



The electrical periods determined by the observations of Mr. Clarke,* 

 of Dublin, are somewhat different. According; to him, the first minimum 

 takes place at three o'clock in the morning ; the electricity then 

 increases till ten o'clock ; it then slightly diminishes till eleven o'clock, 

 then increases anew till two o'clock and forty-five minutes in the 

 evening ; at three o'clock it begins again to decrease, but more rapidly 

 than the first time, till five o'clock ; it then increases till seven 

 o'clock ; then rapidly decreases till it has reached its minimum at 

 three o'clock next day. 



In order to exhibit more clearly these periods of atmospheric elec- 

 tricity, we quote the observations which were made by Schtiblerf 

 on the 11th day of May, 1811, at very short intervals of time, and 

 under a sky constantly clear. We shall follow them by a series of 

 analogous observations, for which we are indebted to De Saussure,^ 

 and add some of those which were made by M. Arago§ at the observa- 

 tory of Paris by means of the straw electrometer. 



Ohserixdions hy Sclrnhhr. 



^" These observations were undertaken at the request of the Royal Irish Academy, and 

 were continued during a whole year. — Philosophical Magazine, vol. XVI, pages 224 and 

 228, 1840. 



f Journal de Schweigger torn. III. Beilage. 



j Voyages dans les Alpes, torn. II, § 802, page 224. 



^Traite de rElectricite et du Magnetisme, par Becquerel, torn. IV, page 93. 



