130 PHYSICAL PHENOMENA OF UPPER REGIONS OF ATMOSPHERE. 



by the wind in gyrations similar to the eddies of water in rivers. 

 Sailors are acquainted with cyclones and water spouts, and dread their 

 dangerous effects. On the American continent there are also observed 

 terrible hurricanes, called tornadoes. These gyratory movements 

 might appear to belong only to great tempestuous disturbances, but as 

 we pursue in detail the study of the atmosphere we find that this kind 

 of disturbance is met with in all the manifestations of displaced air. 

 We conclude from this that the cyclonic movement is in some way the 

 normal state of agitated air. It does not seem possible to use any force 

 upon a gaseous mass without developing in it more or less rapid rota- 

 tions that tend to become permanent. 



Experimental proof . — Whenever we eject a strong jet of gas there are 

 found about it one or more cyclonic currents. The cyclone takes the 

 form of a ring if the ejected column is quite cylindrical, as is seen in 

 the rings of smoke that occur after the explosion of cannon, guns, etc. 



Here was shown the well-known experiment of producing fine 

 wreaths of vapor by striking the canvas bottom of a box filled with 

 vapors of ammonium chloride and having a circular opening in its top, 

 the wreaths being rendered visible by placing them within the range of 

 an electric light. 



Multiple origin of the gyratory movements of the atmosphere. — Almost 

 all the general causes that affect the movement of the atmosphere are 

 gyratory influences; when the movement is once set up it continues of 

 itself and sometimes increases. We ought to mention, in the first 

 place, the rotation of the earth, which always involves a small com- 

 ponent of rotation effecting the displacement of a gaseous mass in 

 latitude or altitude. In the second place, and acting as a controlling 

 cause, we have the solar heat, which warms the air near the ground or 

 the clouds. As the ascensional force of the heated gas can not be uni- 

 form over all tbe surface exposed to solar radiation (both because of 

 the nature and the configuration of the surface), there is a disturbance 

 of the equilibrium at certain points, and columns of air tend to rise. 

 We have then before us the case of the jets already cited, the condi- 

 tions being favorable for gyrations around horizontal axes. When the 

 gyration has once started, the causes that led to it keep it up and 

 increase it. 



The existence of whirlwinds with horizontal axes has been observed 

 in hailstorms (in particular in the storm of May 20, 1893, at Pitts- 

 burg) by an American meteorologist, Mr. Frank W. Very, and has 

 afforded him a very ingenious explanation of the formation of hail. 

 Such a whirlwind, if it is of sufficient size, transports the warm, moist 

 air from the surface of the earth into elevated cold regions. The 

 moisture freezes, and the ice crystals are carried along in the gyratory 

 movement; they alternately rise and fall, following the spirals of the 

 whirlwind, and at every passage into the lower regions, charged with 

 moisture, they increase in size. This explanation accounts for all the 

 special phenomena that we observe in the fall of hailstones ; their zonal 



