45, COEJfHILL, E.G., AND 122, REGENT STREET, W., LONDON, 115 



FIG. 119. 



FIG. 120. 



162. Atmospheric Electricity. The general electrical condition of the 

 atmosphere is positive in relation to the surface of the earth and ocean, becoming 

 more and more positive as the altitude increases. When the sky is overcast, 

 and the clouds are moving in different directions, it is subject to great and 

 sudden variations, changing rapidly from positive to negative, and the reverse. 

 During fog, rain, hail, sleet, snow, and thunderstorm, the electrical state of the 

 air undergoes many variations. The intensity of the electricity increases with 

 hot weather following a series of wet days, or of wet weather coming after a 

 continuance of dry days. The atmospheric electricity, in fact, seems to depend 

 for its intensity and kind upon the direction and character of the prevailing 

 wind, under ordinary circumstances. It has an annual and a diurnal variation. 

 There is a greater diurnal change of tension in winter than in summer. By 

 comparing observations from month to month, a gradual increase of tension 

 is perceived from July to February, and a decrease from February to July. 

 The intensity seems to vary with the temperature. The diurnal variation 

 exhibits two periods of greatest and two of least intensity. In summer, the 

 maxima occur about 10 a.m. and 10 p.m. ; the minima about 2 a.m. and noon. 

 In winter, the maxima take place near 10 a.m. and 8 p.m. ; the minima near 

 4 a.m. and 4 p.m. 



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