260 Proximate Causes of certain Winds and Storins, 



into p and (2 into a. The elevation will not be extended to the 

 whole column, but limited to its lower strata, it being in all cases the 

 ejEFect of the expansion of a given portion of air, to produce a con- 

 densation and displacement of the air in its neighborhood, to which 

 the immediate effect is confined : 8 will therefore be condensed, and 

 at the same time lifted into the position /3, M^here, exerting in the di- 

 rection of ^ the same pressure as when in its original situation, this 

 pressure will not be fully counteracted by the elasticity of ^, but a 

 part of (5 will flow into L Up to this time there could be no motion 

 in the lower strata s and v ; the original pressure upon each remain- 

 ing unchanged, but as soon as a part of (5 flows into &, the pressure 

 upon s being diminished, and the pressure upon v increased, s, the 

 lighter, will give way, and v move in to supply its place. At the 

 same time 5, now in the position ^,' will descend into X. By a con- 

 tinuance of the motion it will sink to v, pass into s, and being heated 

 there, will ascend into its original position L The air thus set in mo- 

 tion, retaining the momentum it has gained, and receiving a new im- 

 pulse from time to time, a horizontal whirlwind moving with greater 

 or less rapidity, will be formed. A person living at the foot of the 

 columns at C and D, and having no notice of what is going on over 

 his head, will suppose there is simply a horizontal wind at his part of 

 the earth's surface, in the direction of vs. A similar motion of air, 

 but in the opposite direction, will be produced by the condensation 

 of the air at ?. 



In every case of wind, the primary movement is upwards or down- 

 wards in a vertical plane. Of this, the horizontal current felt at the 

 earth's surface, is only a- secondary result. It is not possible that it 

 should be generated by those causes which affect the condition of 

 our atmosphere, except according to the methods here represented, 

 and we are warranted in laying down the following proposition. 



The phenomena of winds and storms are the result of a vortex or 

 gyratory movement, generally of no great extent, established in that 

 region of the atmosphere ivhere they prevail. 



To such persons as have been much conversant widi writings on the 

 subject of Meteorology, no apology will be necessary for the formal 

 enunciation of this proposition and the subjoined illustrations. They 

 must be well aware that winds are generally spoken of as long aerial 

 rivers, flowing from one part of the earth's surface to another, with 

 scanty and imperfect, if there are any, notices of the fact, that they owe 

 their existence to another movement of the air at right angles to their 



