THE CLIMATE OF THE LAKE REGION. 211 



every shore, while at night the direction of the breeze is 

 frequently reversed. These are our interior land and 

 sea-breezes. To complete the analogy, our great inland 

 seas exhibit the fluctuations of a diminutive but genuine 

 lunar tide. 



It is impossible that such enormous masses of water 

 should be materially elevated above the mean temperature 

 of the year by three months of summer weather, or de- 

 pressed materially below it by three months of winter. 

 The land surfaces in the same latitudes attain far greater 

 extremes of cold and heat than the lakes. Two reasons 

 exist for this: first, watery surfaces absorb and radiate 

 more slowly; and secondly, the continued stirring of the 

 waters by the winds mixes the surface temperature through 

 a depth of several hundred feet, while on the land the 

 entire effect is confined to a superficial zone of about 

 seventy to ninety feet. The normal mean annual tem- 

 perature of the land in the neighborhood of Milwaukee 

 is 44, and this should be about the mean temperature of 

 the water of Lake Michigan. In summer the Milwaukee 

 mean rises to 67, while in winter it sinks to 22. The 

 water of the lake, meanwhile, rises in summer only to 

 46, and sinks in winter only to 40. Winds from the 

 lake, therefore, partaking largely of the temperature of 

 the water, must exert a material influence in equalizing 

 the land temperatures of summer and winter. Still more, 

 in cases of exti-eme weather, when the land temperature 

 rises to 95 or sinks to 30 below zero, must the amelio- 

 rating influence of such a vast body of water, holding 

 itself steadily at a somewhat uniform tempei'ature, be 

 most conspicuously and most beneficently experienced. 



Observations have shown that even the annual means 



