ELECTRIC STATE OP THE AIR. 



the inferior strata. The globe and its atmosphere may therefore 

 ibe not inaptly compared to a Leyden phial, the outer coating of 

 which being placed in connection with the prime conductor of a 

 machine, is charged with positive electricity, and the inner coating 

 being in connection with the ground, is charged by induction with 

 negative electricity. The outer coating represents the atmosphere, 

 and the inner the superficial stratum of the globe. 



3. This normal state of the general atmospheric ocean is 

 subject to variations and exceptions, variations of intensity and 

 exceptions in quality or name. The variations are periodical and 

 accidental. The exceptions local, patches of the general atmos- 

 phere in which clouds float being occasionally charged with 

 negative electricity. 



4. The intensity of the electricity with which the atmosphere 

 is charged, varies, in the course of twenty-four hours, alternately 

 increasing and decreasing. M. Quetelet found that the first 

 maximum was manifested about 8 A.M., and the second about 

 9 P.M. The minimum in the day was at 3 P.M. He found 

 also that the mean intensity was greatest in January and least 

 in June. 



5. Such are the normal changes which the electrical condition 

 of the air undergoes when the atmosphere is clear and unclouded. 

 When, however, the firmament is covered with clouds, the elec- 

 tricity is subject during the day to frequent and irregular changes 

 not only in intensity but in name; the electricity being often 

 negative, owing to the presence of clouds over the place of 

 observation, charged, some with positive, and some with negative 

 electricity. 



6. The intensity of the electricity of the air is also affected by 

 the season of the year, and by the prevalent character and 

 direction of the winds ; it varies also with the elevation of the 

 strata, being in general greater in the higher than in the lower 

 regions of the atmosphere. The intensity is generally greater in 

 winter, and especially in frosty weather, than in summer, and 

 when the air is calm than when winds prevail. 



Atmospheric deposits, such as rain, hail, snow, &c., are some- 

 times positive and sometimes negative, varying with the direction 

 of the wind. North winds give positive, and south winds negative 

 deposits. 



7. The electricity of the atmosphere is observed by erecting in 

 it, to any desired elevation, pointed metallic conductors, from the 

 lower extremities of which wires are carried to electroscopes of 

 various forms, according to the intensity of the electricity to be 

 observed. So immediate is the increase of electrical tension in 

 rising through the strata of the air, that a gold leaf electroscope, 



N 2 .179 



