RAIN. 457 



add to the annual supply of rain upon that valley, and it 

 therefore exceeds that which falls upon the Alleghanies. 



Those mountains, too, are elevated but about 1500 feet 

 above the table-lands at their base, and do not exert great 

 influence on the counter-trade. If they were 6000 or 8000 

 feet high, a different state of things would exist. 



Again, Mr. Blodget found the quantity of rain which fell 

 in Iowa, and to the south and west of the lake region, to be 

 greater than fell over the lake region itself. 



This, he thinks, is doubtless in part owing to the same cause. 

 The counter-trade, in a stormy state, attracts the surface at- 

 mosphere from the lake region, with its evaporated moisture, 

 before it arrives over it, and, therefore, more rain falls south- 

 west of the lake region than upon it. This power of at- 

 tracting the surface-wind of the ocean in under it, produces 

 the heavy gales which affect our coast, and which are rarely 

 felt west of the Alleghanies to any considerable degree ; and 

 a storm coming from the W.S.W., extending a thousand 

 miles or more from S.S.E. to N.N.W., may have the wind 

 set in violently at southeast on the southern coast first, and 

 at later periods, successively at points farther north, and 

 thus induce the belief that the storm traveled from south to 

 north. 



Of the influence of the Alleghanies, as atmospheric modi- 

 fiers, Dr. Drake records : 



"The mountains bounding the Mississippi Valley on either side 

 deserve great consideration. To the east, or rather southeast, the 

 Appalachian's stretch, in many parallel or coalescing ridges, from 

 Alabama to the region north of the Gulf of St. Lawrence, rising 

 from 2000 to 5000 feet above the sea. They no doubt contribute to 

 some extent to give direction to certain winds. When an easterly wind 

 prevails, they deprive it by condensation (?) of a portion of the moisture 

 with which the warm Atlantic Ocean had imbued it, and reduced its 

 temperature, and hence, on the banks of the Ohio, and in other cen- 

 tral portions of the valley, a southeast wind never raises the tempera- 

 ture as high as a southwest." 



Aside from the general laws of atmospheric phenomena 

 on the Appalachian Mountains of Pennsylvania, there are 



39 



