1397. The northern ice extends during summer about 9ﾦ from the pole; the southern 18ﾦ or 20ﾦ; in some parts even 30ﾦ; and floating ice has occasionally been found in both hemispheres as far as 40ﾦ from the poles, and sometimes, as it has been said, even in latitude 41ﾦ or 42ﾦ. Between 54ﾦ and 60ﾦ south latitude, the snow lies on the ground, at the sea-side, throughout the summer. The line of perpetual congelation is three miles above the surface at the equator, where the mean heat is 84ﾦ; at Teneriffe, in latitude 28ﾦ, two miles; in the latitude of London, a little more than a mile; and in latitude 80ﾦ north, only 1250 feet. At the pole, according to the analogy deduced by Kirwan, from Mayer's Formula, and which is not however found to agree very exactly with what takes place, from a comparison of various observations, the mean temperature should be 31ﾦ. In London the mean temperature is 50ﾦ; at Rome and at Montpelier, a little more than 60ﾦ; in the island of Madeira, 70ﾦ; and in Jamaica, 80ﾦ.
