Snow is _warm_ by virtue of its light and woolly texture. But it is also warm on account of its _whiteness_; for, had it been _black_, it would have _absorbed the heat of the sun_, which would have _thawed the snow_. Instead of which, it _reflects heat_; and the reflected heat _falls upon_ bodies above the snow, while the _warmth of the earth_ is preserved _beneath it_. _White clothing is cool_, because it reflects _from_ the body of the wearer the heat of the sun. _White snow_ is _warm_, because it _reflects the sun's heat upon bodies_. There are few persons but have felt the effect of the sun's rays _reflected_ by the white snow on a clear wintry day. And, as regards the warmth of snow towards the earth, by preventing the radiation of heat, it has been found that a thermometer buried four inches deep in snow has shown a temperature of _nine degrees_ higher than at the surface. 443. _Why are lofty mountains always covered with snow?_ Because the _upper regions_ of the atmosphere are _intensely cold_. 444. _Why are the upper regions of the atmosphere intensely cold?_ Because the _atmosphere_ retains but _little of the heat of the sun's rays_ as they pass to the earth. Because at high altitudes the air is _greatly rarefied_. And because the _radiation of heat from the earth_ does not materially affect such _high regions_. [Verse: "He causeth the vapours to ascend from the ends of the earth: he maketh lightnings for the rain: he bringeth the wind out of his treasuries."--PS. XXXV.] 445. _What is meant by the snow line?_ The _snow line_ is the estimated altitude in _all countries_ where _snow would be formed_. Even at the equator, at an altitude of 15,000 to 16,000 feet from the level of the sea, snow is found upon the mountain summits, where it perpetually lies. As we proceed north or south from the equator the _snow line lessens in altitude_. Had we in England a mountain 6,000 feet high, it would be perpetually _crowned with snow_. 446. _Why do we hear of red snow?_ Red snow is the name given to the snow in the arctic regions upon which a minute vegetable (probably the _Protoccus nivalis_) grows, imparting to the snow a red colour. Recent microscopic investigations have shown it to consist of a minute vegetable cell, which secretes a red colouring matter.