6 ELECTRICITY IN AGRICULTURE 
(d) The vegetation process on the earth, the friction of 
the small solid or liquid particles suspended in the atmo- 
sphere with the air, or between each other, the air’s friction 
against the surface of the earth. 
(e) The direct effect of the sun rays on the different 
layers of the atmosphere. 
A discussion of these very different views cannot be 
entered upon here. I will, therefore, only say that the 
majority of the physicists, as it seems to me, are at present 
inclined to give a certain precedence to the opinion which 
searches for the cause of the atmospheric electricity in the 
evaporation which is going on all over the earth (perhaps 
in connection with the unipolar induction). For my part 
I have no doubt that this conception is right—viz., that the 
watery vapours act as transmitters of the atmospheric 
electricity and carry it to the upper layers of the air, 
because it seems to me that this theory is very well founded 
and in full harmony with other closely allied phenomena. 
According to this opinion, therefore, the evaporation 
must be subjected to the same periodicity as the sun spots 
and also the electrical phenomena in the atmosphere. My 
opinion upon the manner in which Nature is fulfilling all 
this process is shortly as follows :—* 
The quantities of electricity which are carried up by the 
water vapours to the higher parts of the atmosphere reach 
there an air stratum with a low pressure. As this rarefied 
air is provided with a relatively high conducting power, it 
will form with the surface of the earth a nearly spherical 
condenser. The rarefied air space-lies, principally in con- 
sequence of the lower temperature, nearer to the earth 
surface around the poles. Through this circumstance a 
greater quantity of electricity will accumulate in these 
regions, and there discharge in auroral displays or in a 
current from the atmosphere. 
* See also “ L’Aurore Boreale,” by S. Lemstrém. Paris: Gauthier Villars, 
1886, p. 131 and following. 
