'^78 WRITINGS OP JOSEPH HENRY, [1855- 



ihaving consequently a low temperature, will cool the surface 

 of the earth below that of the spaces on either side. 



The pressure of the air in the ascending column will be 

 less than that on the regions north and south, since a portion 

 of its weight is thrown over on either side. This funda- 

 mental principle, which has been strangely mis-understood, 

 will be rendered evident 

 by the annexed figure 8, in 

 which A, B represents the 

 surface of the earth, and a, 

 b, and c, d, (the several par- 

 allel lines above,) the sur- ^ 

 faces of the strata in which FiQ- 8. 



the air is supposed, for illustration, to be divided. The depth 

 of these strata will be throughout the whole column in- 

 creased, and the surface of the upper one will be elevated 

 above the general surface of the atmosphere. Being un- 

 supported, it will tend to flow over on the strata on each 

 side; the surface of the next stratum below will also press 

 outward with more force than it is pressed inward, and 

 will consequently mingle with the air on each side, while the 

 heavy air on each side below opposed by lighter air will 

 press under the lower stratum and tend to elevate it. Be- 

 tween the bottom and the top there will be a neutral surface, 

 marked o, which is in equilibrium. 



In the middle space at the bottom of the ascending column 

 (Fig. 7), the air will be nearly at rest, subject however to fit- 

 ful squalls due to the falling rain, and hence this belt is 

 known either as the belt of rains, or of equatorial calms. 

 The width across the ascending belt is several hundred 

 miles, and though particles of dust or infusoria which enter 

 on the south side may occasionally mingle with the air 

 which enters at the north and thus be carried northward by 

 the upward current, yet the habitual crossing of the two, as 

 some have supposed, and the constant transfer of the vapor 

 of the northern hemisphere to the southern, and vice versa, 

 is in accordance with no established principle of nature, and 

 therefore cannot be admitted even as a plausible hypothesis. 



