332 



ATMOSPHERIC ELECTRICITY. 



{ 



In going over this table we perceive that the intensity of elec- 

 tricity for the two maxima and for the two minima increase perceptibly 

 from the month of July to the month of January, inclusive ; con- 

 sequently that the greatest intensity appears in the winter and the 

 smallest in summer. Moreover the proportion of the mean minimum 

 to the mean maximum is nearly double in the months of summer 

 compared to those of winter, as may be seen in the following table, 

 which comprises the report for the different months of the year, and in 

 which the mean minimum is constantly taken as the unit : 



1811, June 1 : 2.59 



" Julv 1:2.94 



" August 1:2.82 



" September 1:2.94 



'' October 1:2.59 



" November 1:2.32 



^' December 1 : 1.56 



1812, January 1 : 1.80 



*' February 1:2.10 



" March 1:2.29 



'' April 1:2.55 



'' May 1:2.74 



§ 3. Of the prohahle causes of the periodical variations of atmospheric 

 electricity in clear weather. — Many physicists have endeavored to ascer- 

 tain the cause of the daily variations of atmospheric electricity when the 

 weather is clear. De Saussure,* observing that they were in propor- 



* Voyages dans les Alpes, torn. II, sec. 831, p. 256. 



