350 ATMOSPHERIC ELECTRICITY. 



receives a new addition, every time that the rain increases a few 

 moments. It would follow, then, from this that rain should, in 

 general, be negative. According to the English philosopher Foggo,* 

 the electricity, on the contrary, is positive as long as the cloud which 

 pours out the rain is at a distance from the zenith of the conductor, 

 and it only becomes negative when the anterior part of the cloud is 

 above the conductor. This state then continues during a short space 

 of time ; after which positive electricity appears anew, and continues 

 while the cloud is passing over the conductor, to which again succeeds 

 positive electricity. M. Kaemtz states that he has frequently observed 

 positive electricity during rains of short duration. 



We owe to Schiiblert two regular series of observations relating 

 especially to the electricity which is exhibited during the fall of rain and 

 of snow, and which were made, the forraerat EUwangen, from January, 

 1805, to the month of April, 1806, and the latter at Stuttgard, from 

 June, 1810, to the month of August of the following year. In the 

 space of two years and a half Schilbler observed the electricity of 412 

 falls of rain, snow, &c. According to these observations, it is rare 

 that there is rain without electricity ; the phenomenon has not been 

 noticed, except when the electricity of a rain changes from plus to 

 minus, or the reverse ; then the electricity ceases for several seconds. 

 The electricity is again at zero at the commencement, or at the 

 end of a negative rain, as well as at the period of the passage of ordi- 

 nary positive electricity to that of an equally positive rain, and finally 

 during a very feeble rain. When the rain falls in a regular and 

 uniform manner, which is frequently the case, electricity remains 

 for whole days negative or positive ; it varies simply in its intensity, 

 which is generally in proportion to the quantity of water which has 

 fallen. I It is not the same when it rains in an irregular and discon- 

 nected manner ; the electrometer then exhibits oscillations ; the straws 

 diverge, fall back, and their divergence is sometimes positive, some- 

 times negative. 8chiibler remarked that the changes of the sign in 

 electricity corresponded to the difference either in the size of the drops 

 of water or in their number. These facts are frequently observed 

 when isolated waves succeed each other rapidly ; we then frequently 

 find the electricities positive and negative, successively, in the same 

 degree of intensity. The electrical phenomena which accompany 

 the fall of snow are not less complicated ; just as in rain, at every 

 change which happens, either in the form or size of the snow 

 flakes, or in their number, there is a corresponding new electrical 

 state. Schiibler rendered these changes in the intensity and nature 

 of electricity more evident by making, at very short intervals, suc- 

 cessive series of observations, which he represented by curves, in 

 ■which the abscissa expressed the time and the ordinates the cor- 

 responding intensity of the electricity in the degrees of the elec- 

 trometer. 



'-= Edinburgh Journal of Science, volume IV, p. 124. 



t Journal de Schweigger, torn. XXV, p. 249, torn. VIII, p. 21, and torn. XI, p. 377. 

 1829, 1S13 and 1814. 



J This latter hjis aho been established by Beccaria, Ldtere dell' Ekclridsmo, p. 307. 



