THE ATMOSPHERE AND ITS CURRENTS. 



437 



The currents of the atmosphere display an endless variety in their velocity and force, 

 from the zephyr which scarcely stirs the leaves of the forest, to the gale under which its 

 mightiest branches bend, and the hurricane which tears up its trees by the roots, and 

 destroys the habitations of mankind. It has been observed that in the temperate zones 

 the most violent winds occur, when neither the heat nor the cold common to such localities 

 is at its maximum that they generally extend over a considerable tract of country 

 and are accompanied by sudden and great falls in the mercury of the barometer. The 

 latter circumstance attends the storms of the tropics, but they are often confined within 

 narrower limits than the extra-tropical hurricanes. It was noticed by the supperstitious 

 as a coincidence, not without meaning, that at the time of Cromwell's death the enchained 

 winds were liberated, and went forth raving and howling through the land, uprooting the 

 largest trees, and whirling them about like straws, and toppling down chimneys and 

 turrets ; but the same tempest, at the self-same hour, dashed the vessels of the Baltic sea- 

 men upon the strand, and buried Venetian argosies in the Adriatic, shivered the pines of 

 Norway, and swept before it the cypresses of the Bosphorus a similar war of the 

 elements attending the termination of the earthly career of Cardinal Wolsey, Buonaparte, 

 and George IV. Sometimes the upper regions of the atmosphere have been remarkably 

 agitated, while the lower stratum of the air has been quite calm. Lunardi, on one 

 occasion, travelled at the rate of seventy miles an hour in his balloon, while at Edinburgh, 

 where he ascended, the air was quite tranquil, and continued so throughout his expedition. 

 To ascertain the velocity and force of winds, a variety of experiments have been conducted 

 with instruments constructed for the purpose. The following table contains some results 

 obtained by Smeaton, inserted in a volume of the Philosophical Transactions : 



VELOCITY OF THE WIND. 



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 towards 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 recognised titles. 



