450 THE MOUNTAIN. 



a fall of one degree for every three hundred feet (Espy) 

 of ascent into the air, and, under certain circumstances, very 

 much less than that, as, according to Drake,* it is two 

 hundred feet in steep ascents, and four hundred on gentle 

 acclivity as on the Rocky Mountain plains, this cause 

 alone would give diminished temperature on the same line 

 of latitude, as many of the peaks of the range are from 

 three thousand to six thousand feet above the ocean. These 

 high knobs or ranges of elevations, extending as we have 

 seen into the higher currents of air, and catching the 

 counter-trade as it pours down from the heights from which 

 it is deflected from over the tropics, must of necessity be 

 subject to vicissitudes from sudden changes, also extremes of 

 depression from local causes. These are the causes of the 

 great coolness of the mountain and its winds, also the short- 

 ness of its seasons, there being sometimes, in latitude 40, 

 at an elevation of 2000 feet, frost in all months of the 

 year. 



At Cresson, on the Alleghany Mountain, latitude 40 

 30' I" north, longitude west 1 30' 6", and 2000 feet above 

 the sea, there was frost in every month of the year 1859. 

 This is rather a rare occurrence on the central Pennsylvania 

 range. An absence of frost for two or three months is the 

 most general character of summer. f Thus the Indian corn, 

 whose range is to the sixty-fifth degree of mean temperature 

 for the three months of summer, approaches its limit of cul- 

 tivation here, only one or two varieties being at all sure 

 crops, as already noticed. 



RAIN. 



Among hydrometeors, rain forms the most important cli- 

 matic element, hence an inquiry into the different quantities 



* " So peculiar is the vertical distribution of heat, that an eleva- 

 tion of 4000 feet, in some parts of the Rocky Mountain plateau, does 

 not reduce the temperature even one degree." BLODGET. 



f The mean duration of winter at New York, according to Dekay, 

 "is five months, while in the interior northern counties there is frost 

 nearly every month." 



