22 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 51 



The relative motions of the parts of a small circular space on 

 the earth's surface, by reason of the diurnal revolution, are pre- 

 cisely what they would be if the same circular space revolved 

 upon an axis passing through its center parallel to the axis of the 

 globe. If such space be regarded as a plane revolving about such 

 supposed axis, then the relative motions of its parts are the same 

 as if the plane revolved about its center upon an axis perpendic- 

 ular to the plane itself; with* this modification, that an entire 

 revolution on the axis perpendicular to the plane would not be 

 accomplished in twenty-four hours. Such plane daily performs 

 such part of a full revolution about such perpendicular axis, as 

 the sine of the latitude of its center is of radius. The plane itself — 

 the field over which a storm or tornado or a water-spout is form- 

 ing — is in the condition of a whirling table. Hence the tendency 

 to rotary action in every quarter of the storm is equal and all 

 the forces which propel the air towards the center cooperate in 

 harmony to cause the revolution. 



FIG. 4- 



FIG. 5. 



Water discharging from a broad basin through a central orifice, 

 is subject to the same law. It forms a vortex which in our hemi- 

 sphere turns to the left, or against the sun, and in the southern 

 hemisphere must turn to the right or contrary to the sun there. 



These rotations of the atmosphere and of water, being from 

 west to east about lines inclined to parallelism with the earth's 

 axis, are singularly coincident in direction with the rotation of 

 the globe, and harmonize with the general mechanism of the 

 heavens. 



