84 WRITINGS OF JOSEPH HENRY. [1855- 



tend to produce a wind in a westerly direction along the 

 parallel of 60°, which would conflict with the currents from 

 the south, and thus produce a low barometer — a tendency 

 to rain — and form a natural boundary between what may 

 be denominated the polar winds and the belt of westerly 

 winds, due, as we have supposed, to the returning trades. 

 The region of the middle belt must be one of great irregu- 

 larity, occasionally encroached upon by the polar winds of 

 the north on one side and the inter-tropical winds of the 

 south on the other, tending to restore the equilibrium in 

 some cases in the mode suggested by Prof. Dove, and again 

 in that proposed by Mr, Espy. We are however inclined to 

 believe that all these are perturbations in the general circu- 

 lation. 



That the great western mountain system of North and 

 Central America produces an important effect on these cur- 

 rents cannot be doubted, when it is recollected that one-third 

 of the whole atmosphere is below its higher portions. It 

 prevents the northeast trade wind from passing to the coast 

 of the Pacific in about the latitude of 30°, and probably de- 

 flects northeastward a part of the lower portion of the upper 

 return wind, giving more force and quantity to the southwest 

 summer currents than they would otherwise have. This is 

 the view adopted by Mr. Robert Russell, of Scotland, one of 

 the most industrious and promising of the younger meteorol- 

 ogists of Europe, who visited this country about three years 

 ago for investigating its climate and agriculture. It would 

 appear from what has been stated before, that a northwest 

 current most generally prevails in the higher regions, and 

 that the southwest current is a more superficial one. Accord- 

 ing to Mr. Russell, all the disturbances of the atmosphere in 

 this country are produced by the unstable equilibrium oc- 

 casioned by the superposition of the northwest wind on that 

 of the southwest; and this, we think, in connection with the 

 evolution of heat, according to the principles of Mr. Espy, 

 will account for all the violent commotions of our atmos- 

 phere, whether they appear in the form of winter storms, 

 thunder gusts, or tornadoes. 



