388 STATE POMOLOGICAL SOCIETY. 



AN UKSETTLED POINT. 



More recently, however, a doubt is suggested, among persons of high stand- 

 ing in the scientific wiDrld, as to the extent of the ethcacy of forests in deter- 

 mining the amount of the rainfall of a country. 



It is beyond doubt true, that the rainfall of a country may be more or less 

 influenced by other conditions than that of forest growths; such, for instance, 

 as that of the relative positions of mountain ranges, or indeed any other cir- 

 cumstance operating to disturb the horizontal movements of currents of air- 

 Hence, even when admitting the doubtfulness of the theory heretofbre pre- 

 sented, it has yet been urged that if no worse results shall follow the destruc- 

 tion of the forests of a country, it will probably prove true that, from the 

 increasing tendency to the rapid heating and cooling of the exposed surface, 

 with the consequent local creation of atmospheric vortexes, such localities 

 Avhen of considerable extent will be liable to become subject to sudden and 

 deluging showers, and anon to periods of drouth, — the rain clouds passing 

 over them without precipitation. 



From the circumstance that nearly all the phenomena attending the genera- 

 tion of rain occur in an invisible medium, — the atmosphere, — and many of them, 

 moreover, at an elevation above the earth usually quite beyond the reach of 

 direct observation ; our assumptions as to the real causes operating to produce 

 a fall of rain have been based in a considerable degree upon theory. True, it 

 has long been known that air possesses a certain capacity to hold vapor in sus- 

 pension, and that such capacity is increased with the increase of temperature, and 

 diminished by cooling. This quality of the atmosphere having long since as- 

 sumed the dignity of fact, the conclusion became well nigh inevitable that such 

 must be at the foundation of any theory respecting the cause or causes of rain- 

 fall. Still the particular modus operandi by which the result is wrought out 

 has, to a great extent, eluded direct observation. 



At one time meteorologists generally seem to have attributed the precipita- 

 tion mainly to the mixing of currents of air of different temperatures ; under 

 such conditions that the resultant temperature should be such as to compel 

 precipitation of a portion of its moisture, ilore recently, however, the above 

 cause is believed to be less generally operative than had been formerly supposed ; 

 while the result is supposed to be more generally attributable to the elevation 

 and consequent cooling of bodies of air till they are reduced below the point 

 of saturation ; such elevation resulting from being forced up the slopes of 

 mountains, — from being forced upward by other bodies of air getting beneath 

 them, — or from rarefaction by the heat of the sun, and consequent rising. 



METEOROLOGISTS 



have long known that the Caribbean Sea and the Gulf of Mexico, with their 

 torrid climate and almost tepid waters, not only supply the great "Ocean 

 River," the Gulf Stream, with the warmth which its waters transmit across the 

 Atlantic, and which so wonderfully ameliorates the climate of northwestern 

 Europe ; doubtless, at the same time, becoming one of the chief causes of the 

 tornadoes that so terribly devastate the AVest Indies, and the southeastern 

 United States; but that they also supply a passage way for that great a3rial 

 river, the northerly branch of the deflected trade wind, which sweeps over their 

 waters, along the northern coast of South America; whence, still further de- 

 flected by the Central American, Mexican, and Rocky Mountains, it is con- 

 verted into an immense eddying vortex, covering the United States and the 



