-1859] WRITINGS OF JOSEPH HENRY. S^ 



atmospheric disturbances. We say principally, because a 

 portion of the surface northeast trade wind in summer prob- 

 ably blows over Florida and the lower part of Louisiana. 

 These views have been strengthened by a series of observa- 

 tions collected by M. De Done, from which it is shown that 

 the winds from the western half of the horizon, as indicated 

 by the clouds, preponderate over those from the east, as 

 indicated by the wind vane at the surface; or in other 

 words, that there is a greater tendency to a movement, even 

 in our latitude, in the upper strata of air from the western 

 half of the horizon, and in the lower from the eastern — a 

 result in conformity with the general principles we have 

 endeavored to explain. The circulation in the region of 

 variable winds may ofte^ be inverted, and the compensation 

 take place by means of winds in different parts of the hemi- 

 sphere. It must be evident from mechanical principles that 

 to balance every current of wind which flows to the north 

 over any parallel of latitude along any meridian an equal 

 amount must flow back to the south either along that 

 meridian or some other. If the compensation takes place at 

 the same meridian, one current must flow above and the 

 other below. If at difierent meridians, the compensating 

 currents may both be at the surface or both above. The 

 fact that very different temperatures prevail at different parts 

 of the world at the same time under the same latitude favors 

 the idea of Prof. Dove that the compensation does in many 

 cases take place in the latter way. Mr. Espy supposes that 

 our southwest wind is produced mainly by the descent of 

 the return trade winds at about the 30th parallel, and by 

 rains accompanied with an elevation of temperature, and 

 consequently an ascent of air at the parallel of 58° or 60°, 

 and that it returns again in an upper current over the belt 

 we have described towards the south. That whatever air 

 reaches the polar regions should descend there and flow 

 southward, and then rapidl}'' decline to the west, appears to 

 be an evident consequence of well established laws. The 

 rapid inclination of the air on account of the great increase 

 of rotation in the surface of the earth in this latitude would 



