54 WRITINGS OF JOSEPH HENRY. [1855- 



tem of circuits inclined to the west; the eastern portion of 

 which would be at the surface, and the western at different 

 elevations even to the top of the atmosphere. To give 

 definiteness to the conception, let us suppose a series of 

 books to be placed side by side on edge, pointing to the 

 north ; these books would represent the planes in which the 

 currents of the air would circulate in the northern hemis- 

 phere, were the earth at rest; but if the earth is supposed 

 to be in motion, then the books must be inclined to the 

 west, so as to make an acute angle with the horizon, and 

 overlap each other like the inclined strata in a geological 

 model. If on each leaf of each book a circuit of arrows be 

 drawn, then will the assemblage of these represent the paths 

 of the different particles of the atmosphere. The currents of 

 air however would not be in perfect planes, but in surfaces 

 which could be represented by bending the leaves to suit 

 the curvature of the earth. In this manner would be ex- 

 hibited the general motion of the wind, which has been de- 

 termined by actual observation. 



The greater portion of the circulation would descend to 

 the earth within 30 degrees of the equator, giving rise to the 

 trade winds; a portion would flow further north, and pro- 

 duce the southwest winds; another portion would extend 

 still further northward, descend towards the earth as a north- 

 west wind, and so on. The air which descends in the region 

 of the pole would not flow directly southward, but, on ac- 

 count of the rotation of the earth, would turn towards the 

 west and become a northeasterly current. At first sight it 

 might appear that the north wind which descends from the 

 polar regions would continue its course along the surface 

 until it joined the trade winds within the tropics ; but this 

 could not be the case, on account of the much greater 

 western velocity this wind would require from the rapidly 

 increasing rotary motion as we leave the pole. There would 

 therefore be three distinct belts in each hemisphere, namely, 

 the belt of easterly winds within the tropics, the belt of 

 westerly in the temperate zone, and the belt of northwesterly 

 at the north. The existence of these belts has been clearly 



