Electricity in Agriculture and Horticulture #227221

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 60 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.