1850.] 95 



This constant progression of vast nnasses of vapor, of copious showers, and 

 successive thunderstorms, along the mountainous but broken range of the Isthmus, 

 appears to be chiefly from the equator, northward. 



More than forty years ago, the celebrated Humboldt offered an explanation 

 of the causes which occasioned the insupportable heat and dryness of the Old 

 World, within the limits of the torrid zone, and the comparative coolness and 

 continued humidity of the same parallel on the New Continent. These views 

 are repeated in the same author's recent work on the " Aspects of Nature." I 

 may be permitted to give the substance of them here. 



In the sandy deserts of Africa, the vertically ascending column of warm air 

 prevents the vesicles of vapor from being dissolved. The more complete the 

 absence of vegetation and the more the sand is heated, the greater is the height 

 of the clouds, and the less can any fall of rain take place. Thus, in deserts, the 

 want of rain and the absence of vegetation, act and react upon each other. It 

 does not rain, because the naked, sandy surface, having no vegetable covering, 

 becomes more powerfully heated by the solar rays, and thus radiates more heat ; 

 and the absence of rain forbids the desert being converted into a steppe or grassy 

 plain, because without water no organic development is possible. 



On the contrary, in the New World, beneath the torrid zone, among other 

 causes that tend to create a cooler and moister climate, are enumerated the 

 impenetrable forests which occupy the alluvial plains which are situated immedi- 

 ately beneath the equator; protecting with their shade the soil beneath from the 

 direct influence of the sun beams, and exhaling in the interior of the country, at 

 a great distance from the mountains and from the ocean, vast quantities of moist- 

 ure, partly imbibed and partly elaborated. It is to the same causes that we are 

 to attribute the luxuriant vegetation, the magnificent forests, and that abundant 

 leafiness by which the New Continent is peculiarly characterized. 



Dr. Bridges presented a paper from Mr. James Deane, of Connecti- 

 cut, on the " Fossil Foot-prints of Connecticut River," intended for 

 publication in the Journal. Referred to Drs. Bridges, "Wilson, and 

 Leidy. 



Dr. J. K. Townsend read a paper describing a new species of 

 American Wolf, (Lupus gigas, Townsend, the giant wolf of N. America:) 

 which, being intended for publication in the Journal, was referred to 

 a committee, consisting of Drs. Hallowell, Wilson, and Morton. Dr. 

 T. stated that the skin and skull of the animal described in his paper, 

 were in the possession of the Academy, and would be mounted at an 

 early period. 



Mr. Cassin read a paper, entitled "Descriptions of new species of 

 Birds collected by Mr. John G. Bell, in California." Referred to a 

 committee, viz. ; Drs. Wilson, Townsend, and Leidy. 



