334 ATMOSPHERIC ELECTRICITY. 



little before sunrise, and that it increases but slowly during the rising 

 of this luminary_, the increase being very small in the first hour; at the 

 same time the hygrometer advances but little at first, and in a man- 

 ner barely perceptible, towards dryness. Soon after the electricity 

 increases rapidly, and it attains (some hours later) toward eight 

 o'clock its first maximum. At this time of day the temperature of the 

 air rises quite rapidly ; the hygrometer likewise advances some de- 

 grees towards dryness ; but if we reduce by calculation its indications 

 to the same temperature, it is found that the absolute moisture of the 

 air, instead of decreasing, rather increases in the first hours which 

 follow sunrise. When the electricity has reached its first maximum 

 and begins to decrease, the lower strata of the air lose their moist 

 condition ; the atmosphere becomes clear, and the sky assumes insen- 

 sibly a pure blue. It is also at this period that the dryness of the 

 air becomes real, which is clearly announced by the hygrometer. 

 About two o'clock in the afternoon the electricity is very feeble, and 

 near its second minimum; it contributes to decrease a little in summer, 

 until towards four or five o'clock. Now, we may observe that this 

 is precisely the period of the greatest real dryness in the air. An hour 

 before sunset the electricity begins anew to increase, though slowly ; 

 it shows itself more and more in proportion as the sun descends ; and 

 a little time after it disappears below the horizon it increases more 

 rapidly, and soon after reaches its second maximum; also, during 

 this time light vapors appear in the atmosphere. At sunset the air 

 had lost its transparency, the moisture rapidly increased, the fresh- 

 ness of the evening came on, and the dew is formed. From this mo- 

 ment the electricity decreases with the actual moisture of the air. 



The relation between the progress of atmospheric electricity 

 observed by Schiibler and that of the hygrometric state of the air iji 

 the course of the day is then evident. It is the same for the'periods of 

 the mean maxima and minima of the year ; for, if we examine the 

 table which contains the intensities of the electricity for the different 

 months, we observe that the intensity is the strongest in the month of 

 January and most feeble in the months of April and May. Now_, 

 it is precisely the same periods which exhibit the extremes of the rela- 

 tive humidity of the air.* It is, therefore, no longer doubtful, as De 

 Saussure was the first to observe, that the daily variations of atmospheric 

 electricity are only the result of the changes which take place 

 in the hygrometric state of the air. Schiiblerf advanced the same 

 opinion; but, admitting Volta's theory, he found the explanation in 

 the electricity which the vapor conveys to the air in a latent state, 

 and which it set free at the moment of its passage to the state of 

 vesicles. 



We know that it is not in the greater or less quantity of positive 

 electricity conveyed by the vapor of the atmosphere that we must 

 seek for the cause of the daily variations of the electricity, since the 

 circumstances which attend the formation of vapor give the air suf- 

 ficient conducting power to produce the decomposition of the electric 

 fluids liberated at the instant. — (See page 316.) We know, further, that 



~ Lelirbi'.ch der Meteorologio, von L. F. Kaemtz, torn. T, p. 337. 

 t JourLal de Schweigger, torn. VIII, p. 29. 



