──────┬───────┬─────────────────────────┬───────────────────────── Miles │ Feet │ Perpendicular Force on │Characteristics. per │ per │ one Square Foot, in │ Hour. │Second.│ Avoirdupois Pounds and │ │ │ Parts. │ ──────┼───────┼─────────────────────────┼───────────────────────── 1 │ 1·47 │ .005 │Hardly perceptible. ──────┼───────┼─────────────────────────┼───────────────────────── 2 │ 2·93 │ ·020 } │Just perceptible. 3 │ 4·4 │ ·044 } │ ──────┼───────┼─────────────────────────┼───────────────────────── 4 │ 5·87 │ ·079 } │Gentle, pleasant wind. 5 │ 7·33 │ ·123 } │ ──────┼───────┼─────────────────────────┼───────────────────────── 10 │ 14·67 │ ·492 } │Brisk wind. 15 │ 22 │ 1·107 } │ ──────┼───────┼─────────────────────────┼───────────────────────── 20 │ 29·34 │ 1·968 } │Very brisk wind. 25 │ 36·37 │ 3·075 } │ ──────┼───────┼─────────────────────────┼───────────────────────── 30 │ 44·01 │ 4·429 } │High wind. 35 │ 51·34 │ 6·027 } │ ──────┼───────┼─────────────────────────┼───────────────────────── 40 │ 58·68 │ 7·873 } │Very high wind. 45 │ 66·01 │ 9·963 } │ ──────┼───────┼─────────────────────────┼───────────────────────── 50 │ 73·35 │ 12·300 │Storm. ──────┼───────┼─────────────────────────┼───────────────────────── 60 │ 88·02 │ 17·715 │Great storm. ──────┼───────┼─────────────────────────┼───────────────────────── 80 │117·36 │ 31·490 │Hurricane. ──────┼───────┼─────────────────────────┼───────────────────────── 100 │ 147·7 │ 49·200 │Hurricane carrying trees │ │ │and buildings before it. ──────┴───────┴─────────────────────────┴───────────────────────── The currents of the atmosphere far surpass in velocity those of the rivers and the ocean, a gentle pleasant wind blowing at a rate equal to that of the mighty Father of Waters when in flood, but a hurricane will outstrip the swiftest locomotive in its speed. In speaking of the direction of currents of air and water, the indicating terms are employed in an inverse sense, an easterly wind signifying a breeze coming from that quarter, an easterly stream a flow of water toward it. Winds may be divided into three classes or genera, the Permanent, the Periodical, and the Variable; of which, the first excepted, there are many different species. We shall prefer, however, to consider them under their local recognized titles. [Illustration: =A Calm at Sea.=]