62 WRITINGS OF JOSEPH HENRY. [1855- 



poles, would sink to the earth, flow back to the equator 

 below, and would again be elevated in an ascending cur- 

 rent; and thus a perpetual circulation from either pole to 

 the equator, and from the equator back towards the poles, 

 along the several meridians of the globe, would be the con- 

 tinuous result. It is further evident that since the meridians 

 of the earth converge, and the space between them constantly 

 becomes less, all the air that rose at the equator would not 

 flow along the upper surface entirely to the poles, but the 

 greater portion would proceed north and south no further 

 than the 30° of latitude; for the surface of the earth con- 

 tained between the parallel of this degree and the equator 

 is equal to that of half of the whole hemisphere. Portions 

 however in the northern hemisphere, for example, would 

 flow on to descend at different points further north ; and of 

 these some would probably reach the pole, there sink to the 

 surface of the earth, and from that point diverge in all direc- 

 tions in the form of a northerly wind. Between the two 

 ascending currents near the equator would be a region of 

 calms or variable winds, influenced by local causes. The 

 currents which flow over towards the poles would descend 

 with the greatest velocity at the coldest point; because there 

 the air would be most dense, or would have the greatest spe- 

 cific gravity. 



According to the view here presented, a section of the 

 atmosphere made by cutting through a meridian from pole 

 to pole, perpendicular to the horizon, would exhibit two 

 great systems of circulation ; one from the north and another 

 from the south to the equator below, rising at the latter 

 place, and pouring over on either side to return again by 

 longer or shorter circuits to the place whence they started. 

 Such would be the simple circulation of the aerial ocean if 

 no perturbing influences existed, and the whole science of 

 meteorology would be one of comparatively great simplicity. 

 But this is far from being the case. A number of modifying 

 conditions must be introduced, which tend greatly to per- 

 plex the anticipation of results. First, the earth is not at 

 rest, but in rapid motion on its axis from west to east. 



