212 



WRITINGS OF JOSEPH HENRY. [1855- 



METEOKOLOGY IN ITS CONNECTION WITH AGRICULTURE. 



PART IV. — ATMOSPHERIC VAPOR AND CURRENTS. 



(Agricultural Report of Commissioner of Patents, for 1858, pp. 429-493.) 



In the preceding articles on Meteorology, it has been shown 

 that the great motive power which gives rise to the various 

 currents of the aerial covering of our globe is the unequal 

 distribution of the heat of the sun ; the elevated temperature 

 of the equatorial regions heating the air causes it to ascend 

 and flow over toward the pole, while the cold of the frigid 

 zone produces a condensation of the air, which gives rise to 

 downward currents in that region, and a spreading out there 

 in all directions towards the equator. 



The simplicity of this movement is first interfered with by 

 the motion of the earth upon its axis, which gives to all the 

 currents flowing toward the equator a curvature to the west, 

 and to all those flowing from the equator a curvature to the 

 east. Another perturbing influence is the unequal heating 

 of the several parts of the different zones of the earth, con- 

 sisting as they do of alternations of land and water. But the 

 great perturbing cause is the varying quantity of moisture 

 which exists in the atmosphere, and which by its increase 

 and diminution gives rise to the varying conditions of the 

 weather, and produces the fitful and almost infinite variety 

 of meteorological changes which occur at different times and 

 in diff'erent places. 



The present essay will be principally devoted to an expo- 

 sition of the phenomena of the vapor of the atmosphere, in- 

 cluding that of the various aqueous meteors, such as rain, 

 hail, hurricanes, tornadoes, &c. The meteorology of North 

 America, as well as its geology, is exhibited on a large scale, 

 and affords one of the best fields on the surface of the globe 

 for studying the general movements of the atmosphere. The 

 subject has received much attention on this side of the At- 

 lantic, and a number of laborers have devoted themselves to 

 it with ardor and success ; but we regret that the discussions 



