The atmosphere is the vast ocean of air that envelops the earth and
makes life possible on our globe. It absorbs the heat and vapors
caused by the action of the sun upon the surface of both land and
water, and is the medium through which the ever-changing phenomena
of _climate_ and _weather_ are produced. The two great forces of
nature acting in connection with it are _gravitation_ and _heat_, or
solar radiation; and the results of their ceaseless action may be
summed up as follows: (1) _Temperature_, or heat, which we soon
learn to know by our senses, and to measure by the thermometer. (2)
_Evaporation_, which changes the weight of the air by carrying
invisible moisture through it. This change of _weight_ is indicated
by the barometer. (3) _Condensation_, producing fog, dew, rain,
hail, and snow; all estimated accurately by the rain gauge or
pluviometer. (4) _Motions_, as in the winds, varying from the gentle
breeze to the awful cyclone, the force and velocity of which are
indicated by the anemometer. (5) _Electricity_, producing lightning,
thunder, magnetic and chemical changes in the atmosphere. (6)
_Optical Phenomena_, such as rainbows, haloes, coronas, mirage, and
the auroras.
_THE ATMOSPHERE: ITS EXTENT, CHARACTER, USE AND EFFECT_
The Earth is enveloped in its own atmosphere, which like a transparent
covering surrounds it, and revolves with it. This atmosphere does not
extend to more than forty or fifty miles above the earth’s surface, and
is higher at the equator than at the poles.
[Illustration]