1391. Frost, being derived from the atmosphere, naturally proceeds from the upper parts of bodies downwards; so, the longer a frost is continued, the thicker the ice becomes upon the water in ponds, and the deeper into the earth the ground is frozen. In about sixteen or seventeen days' frost, Boyle found it had penetrated fourteen inches into the ground. At Moscow, in a hard season, the frost will penetrate two feet deep into the ground; and Captain James found it penetrated ten feet deep in Charlton Island, and the water in the same island was frozen to the depth of six feet. Scheffer assures us, that, in Sweden, the frost pierces three feet (a Swedish ell) into the earth, turning what moisture is found there into a whitish substance, like ice; and into standing water three ells or more. The same author also mentions sudden cracks or rifts in the ice of the lakes of Sweden, nine or ten feet deep, and many leagues long; the rupture being made with a noise not less loud than if many guns were discharged together. By such means, however, the fishes are furnished with air, so that they are rarely found dead.