LOCAL CLIMATOLOGY. 75 



These bodies of water cool the air in summer, and warm it in 

 winter. 



Let us suppose, first, that the air is below 32 deg. While the 

 lake is open, the air will be warmed by contact with the water 

 and by radiation from it. It has been ascertained by experiment 

 that one cubic foot of water, in cooling one degree Fahrenheit, 

 gives out heat enough to raise 3080 feet of air one degree, or 300 

 feet about ten degrees. 



But again : When the water becomes cold enough to freeze, 

 and freezing commences, the solidification gives out what is called 

 the " li(tal of liquefaction f and this, in the formation of one cubic 

 foot of ice, is sufficient to raise 691.922 feet of air one degree, or 

 34.596 feet of air twenty degrees, or 13.854 feet fifty degrees. 



Doubtless the tendency of the air, thus heated, is to rise 

 directly upw^ard. But rather than ascend directly through the 

 mass of colder air immediately over it, it is driven by the winds ; 

 and even when there are no winds of any considerable force, it 

 will creep along up the banks of the river or lake, and the sides 

 of the adjoining eminences, softening and modifying their climate 

 by its approach to them. 



On this point I have no statistics within my reach, except such 

 as have been derived from my own observation. January 8th, 

 1855, the thermometer indicated 7 deg. above at 7 a. m. in my 

 Observatory. At a private residence only a few miles west, back 

 of the lake, it stood at zero ; and at Phelps, eight miles northwest, 

 it was reported at 7 deg. below ; and I have observed similar 

 discrepancies in other cases. Even to the east of us, and between 

 the two lakes, Seneca and Cayuga, the temperature is always 

 found to be several degrees colder when the thermometer reaches 

 a figure below zero. 



Of course, wdien a lake becomes entirely frozen over, or frozen 

 out a long distance from the shore, it ceases to influence the tem- 

 perature in the w^ay I have described : in the one case, because 

 there is no longer any open surface of water ; and in the other, 

 because it is so far oif, and is separated from the land by a level 

 surface along which the warm air will not pass as it w^ould if it 

 w^ere ascending. 



The heat thus given out by the cooling of the water and the 

 formation of ice in the autumn and early winter, would of course 

 be returned in the spring when the ice thaws and the water is 

 gathering its warmth for summer. Hence, while this cause will 



