352 



ATMOSPHEEIC ELECTRICITY. 



every montli, as well as the number of days of rain or of snow during 

 which the electricity was negative or positive.* 



We may add to this table the general remark that rains exhibit an 

 electricity which is strong in proportion as they are abundant in a 

 given time. This stronger electricity accompanies showers — always 

 transient rains and storms. 



We have seen above that Volta in general found that the elec- 

 tricity of the rain which he observed was negative. If in Schiibler's 

 observations, of which we have already given a summary, we re- 

 capitulate separately the number of days of rain or snow during 

 which the electricity has been positive or negative, we find, on the 

 contrary, 71 days positive and 69 negative, that is to say almost 

 the same number of positive as negative days. The observations made 

 by Hemmer,t at Mannheim, from 1783 to 1787, lead to the same 

 result; he found these two numbers in the ])roportion of 1 to 1.08. 

 According to the observations of M. Arago,;{; during the first seven 

 months of 1830, there were eleven days of rain without electricity, 

 six days with positive electricity, and eight days with negative electri- 

 city. From the collective result of these different observations, we 



■~" To obtain the numbers contained in this table, Schiibler noted separately the degrees 

 of positive electricity and those of negative electricity. Where the electricities of different 

 nature alternated, he added apart the degrees observed and corresponding to the rains or 

 snows, positive as well as negative: and, if one of these two electricities preponderated, 

 he kept a proportional account. When a rain or snow gave signs of only one electricity, 

 but with a varial>le intensity, he placed it at the higher degree in the account. Finally, 

 be did not measure the electric tension beyond 600 degrees of the straw electrometer; then 

 the electricity began to give out sparks, and a small Leyden phial, which was charged 

 with free air. gave quite powerful shocks. 



f Lehrbnch der Metcorologie, von Kaemtz, tom. II, p. 418. 



JTraitc d'Elcctricitc et du Magnet., par Becquerel, tom. lY, p. 100. 



