336 ATMOSPHEKIC ELECTRICITY. 



But it is not necessary to conclude from what has been said that i*- 

 is in radiation only that the cause of the daily variations of atmos" 

 pheric electricity is found. We shall see, in speaking of the formation 

 of electric clouds, that the sum of the facts tends to prove that the 

 vapors reach the air charged with negative electricity, and that it 

 weakens by its presence the higher positive influence to which the in- 

 struments are subjected, so that the indication of the electrometer must 

 still decrease in the course of the day proportionally to the quantity 

 of the vapor which rises in the air. But to appreciate the effect pro- 

 duced by this latter cause it is necessary to render the observations 

 independent of the electric radiation of the instrument. 



It has been remarked that a certain relation might be observed 

 between the variations of atmospheric electricity and the other phe- 

 nomena which take place periodically on the surface of the earth. 

 For example, according to Mr. Kaemtz,* these variations are not per- 

 haps without relation to the phenomena which accompany vegetation. 

 It is known that, under the influence of solar light, plants give out 

 oxygen, and that during the night they exhale carbonic acid. The 

 former of these two opposite phenomena would be the most active 

 when the sun is nearest the zenith, and the latter when this body 

 approaches the horizon. Mr. Kaemtz thought that these two differ- 

 ent modes, in which the plants acted on the air, could not be without 

 some other influence on the daily variations of the electricity. But 

 if we admit this opinion we must prove that the electric phenomena 

 observed by M. Pouillet in his experiments on vegetation are, in fact, 

 produced by the cause which this philosopher assigned to them. 



Schiibler thought he observed a correspondence between the oscilla- 

 tions of the magnetic needle and the electric periods. f The point of a 

 horizontal magnetic needle turned to the north in fact moves from 

 the east to the west, from eight and a half o'clock in the morning till 

 one hour and a quarter after noon, and from west to east from one and 

 a quarter hour in the afternoon till the next day morning. There 

 is then a maximum of departure to the east, which takes place at eight 

 and a half o'clock in the morning, and another to the west towards 

 one and a quarter o'clock. Finally the same philosopher^ made the 

 observation that the daily variations of atmospheric electricity corre- 

 spond very well with those of the barometer, the maxima also taking 

 place for the latter as well as for electricity later in winter than in 

 summer. 



* Lehrbuch der Meteorologie, torn. II., p. 411. 

 t Journal de Physique, torn. LXXV. p. 177. 1812. 

 J Journal de Schweigger, torn. Ill, p. 12G. 



