[Frost and fire : natural engines, tool-marks and chips : with sketches taken at home and abroad by a traveller] . dust. Then the real distance ismeasured by the help of the grand soimd of a falling aval-anche, and the giants assume their true proportions. The sea of cloud which surges agamst the mountain a fewhundred feet below the peak, changes its shape at everymoment, as currents of air rise from glens below. The atmo-sphere is all in motion, though there may be no generalhorizontal movement at a particular spot and time. But, when the sim sets, this local motion gradually de-creases, and
[Frost and fire : natural engines, tool-marks and chips : with sketches taken at home and abroad by a traveller] . dust. Then the real distance ismeasured by the help of the grand soimd of a falling aval-anche, and the giants assume their true proportions. The sea of cloud which surges agamst the mountain a fewhundred feet below the peak, changes its shape at everymoment, as currents of air rise from glens below. The atmo-sphere is all in motion, though there may be no generalhorizontal movement at a particular spot and time. But, when the sim sets, this local motion gradually de-creases, and cold moon-beams may play upon a qviiet stagnantsilvery ocean of gray cloud resting becalmed upon hill andplain, or creeping slowly upon still water. 28 ATMOSPIIEBIf FORMS. We live in a sea of boiling air, and when its local move-ments are made visible by clouds ; beat, cold, and gravitation—radiating and converging forces—are seen at work in theatmosphere. Force is revealed by form. On these forces and on these movements depend all atmo-spheric changes and the science of meteorology, which treatsof Fifi. 8. Diagram of tiik AVinds, by Lieut. Maury, Abstracts of Meteorological Observations, etc., edited hy : Eyre and Spottiswoode, lS5fi. CHAPTEE VI. METEOROLOGY. The modern science of meteorology is founded upon upw^ardand downward movements in the whole atmosphere. All storms have been traced to the movements of twogreat currents in each hemisphere, which move like local cur-rents, and for the same reason. These are north-east or northpolar, south-west or equatorial, in the northern hemisphere ;south-east or south polar, north-west or equatorial, in thesouthern hemisphere. These great currents are attributed to upward and down-ward movements :—to the rising of light warm air near theequator, and to the falling of heavier colder air at the movements then, whether large or small, generalor local, are attriljuted to the a
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