AEEIAL EDDIES. 273 



: BOOK II.— HUEEICANES AND WHIELWINES. 



CHAPTEH IX. 



AERIAL EDDIES. — CYCLONES OF THE EQUATORIAL REGIONS. — THE "GREAT 

 HURRICANE." 



It is probable tliat the wind is never propagated in a straight line. 

 If it were it would be because it did not meet, in its course, any salient 

 points of the surface of the earth, nor strike against any other masses 

 of air, either at rest or moving in opposite directions. The atmospheric 

 currents having always to strive against obstacles of this nature, 

 must necessarily rebound to right or left, and advance by a series of 

 eddies similar to those which the waters of a river form at the meet- 

 ing of two currents. It is thus that a sudden wind raises the 

 dust from the high road, or drives before it the leaves of the forest. 

 In the same way, during the winter days, when unequal breezes chase 

 each other in the atmosphere, the flakes of snow, in descending, describe 

 long spirals, and the smoke which rises unrolls itself in circles of an ever- 

 increasing diameter. The particles of air, like the heavenly bodies 

 themselves, revolve as they move.* If two gusts of air meet at the 

 entrance of a valley, and are continued in long eddies, the circular 

 movement is continued from place to place, like a wave on the surface 

 of the water^ and the entire aerial mass is disturbed in its equilibrium. 

 In all the regions of the atmosphere, where two currents strike one 

 another directly, or come in contact laterally, aerial eddies are in- 

 stantly produced on the line of meeting, which move with extreme 

 rapidity, and their vast whirls soon re-establish the equilibrium be- 

 tween the two masses of air. When these eddies have only a local 

 importance they are known under the name of whirlwinds ; but when 

 their effects are felt over a great extent of country, the more general 

 and more scientific designation of cyclone, proposed by Piddington, is 

 * Carus, Natur und Idee. 



T 



