2 ELECTRICITY IN AGRICULTURE 
40 bushels, and from barley 20 bushels, and so forth. It is 
the same with grass. These results are attained although 
the people cultivate their soil very imperfectly, using only 
ploughs and harrows of wood. 
Vegetables require, for a rich development, a fertile soil 
and a sufficient quantity of heat, light and humidity ; but 
one of these principal conditions, that of heat, is to be 
found only in a slight degree in the Polar regions. To be 
convinced of this it is only necessary to glance at a map 
and follow the yearly isothermes, and especially the 
summer isothermes. The isotherm corresponding to a 
mean temperature of —7°C. to —8°C. crosses Spitzbergen, 
and that of o’C. goes through the north of Finnish Lapland. 
The mean temperature for the month of July is there 10°C., 
and at Spitzbergen 5°C.* 
The cause of the astonishing development of vegetation 
under such conditions has hitherto been held to lie in the 
long day, which lasts from two to three months in these 
regions during their short summer. It is further sometimes 
supposed that this circumstance will provide the crops with 
more light and heat, the principal factors of vegetation. 
This is, however, not true, for calculation shows that the 
quantity, notwithstanding this long day, is less than it is, 
for instance, in 69 deg. of latitude. In consequence of the 
low height of the sun over the horizon, the rays meet the 
earth in such an oblique direction that their illuminating 
and heating power is greatly lessened, and this power is 
also lessened by the great absorption in the atmosphere, 
Since the quantities of light and heat received are relatively 
smaller than in more southern regions, the cause of the rich 
development of the vegetables cannot lie in the long day, 
and must be sought elsewhere. 
For several reasons I was induced to search for the 
cause in electrical currents, the effect of which appears in 
the Polar light, and which are going from the atmosphere 
* See Thermometer Table at end of book. 
