LOCAL CLIMATOLOGY. 103 



greatly increased in the eastern part of our continent and in the 

 AtUintic ocean, by the fact already pointed out, that they are the 

 great wind-gap of the northern hemisphere. And although the 

 general causes of these phenomena may exist and be active in the 

 southern hemisphere, I doubt whether, without the peculiar con- 

 formation of the mountains in our hemisphere, to give them in- 

 tcnsit3% their influence would be particularly noticeal)le. 



Besides these local causes influencing climates, there are one or 

 two more phenomena suggested by the meteorological observa- 

 tions in my possession, that I will put on record here as worthy 

 of observation. 



1. The first is this : It has happened thus far, that when the 

 winter comes on gradually and continues cold through January 

 and the first half of February, without much of what is called the 

 "January thaw," we have an early spring, and the snow passes 

 ofi" and the frost comes out of the ground earlier than when the 

 winter is what is commonly called an " oj^e/t" one. The observa- 

 tions in my possession suggest this rule, and perhaps it is what 

 we should expect on general principles. 



2. Ao-ain : when there is a laro-e accumulation of snow and ice 

 during the winter in the region northwest of us, and especially to 

 the northwest of the great lakes, the spring, though it may be an 

 early one, is sure to be attended with an unusual number of cold 

 rains, chills, and even frosts. The reason for this is obvious. 



It forms no part of my plan to discuss the distribution of rain ; 

 but there is one remark that is so connected with my su])ject, that 

 I will beg a fcAV words more, for the purpose of saying it. As a 

 general rule : 



1. The amount of water that falls annually, decreases from the 

 equator to the poles. 



2. It decreases from the sea coast as we pass inward towards 

 the centre of the continent. 



3. It is, in the northern hemisphere, greater on the south and 

 west sides of mountains than on the north and east sides. 



Now, OAvinof to these laws combined, it is doubtful if we should 

 have rain enough for successful agriculture in the Avestern and 

 central States of the United States, were it not for our great lakes. 

 On the coast most of the rain comes from the ocean ; but in the 

 neighborhood of the lakes, as Geneva, for example, so far as I 

 can judge, quite one-half of the water that we have in the year, 

 is by evaporation from the lakes, most of which, being west of 



