CLIMATIC INFLUENCES OF BODIES OF WATER 145 



160. Reason for difference between east and west shores. A 



reason for the difference between the east and west shores is 

 not difficult to find. It will be recalled that in connection 

 with the study of the wind movements of the earth we found 

 that the United States is in a' belt of prevailing westerly 

 winds. We have winds from all points of the compass, but 

 our winds much more frequently blow from a point west of 

 a north-and-south line than from a point east of such a line. 

 They are usually southwest, west, or northwest. It follows 

 from this that on most days of the year the air over the coun- 

 try to the east of the lake has come across the lake. On the 

 west side the influence of the lake is very slight excepting on 

 a few days when the wind is from some easterly direction or 

 when the west wind is so light that a lake breeze develops. 

 The effect of the lake is particularly important in case of a 

 cold wave, for our coldest winds are from the northwest. This 

 is well illustrated by the cold wave for which temperatures 

 are given. 



161. Some general conclusions. We are safe in concluding, 

 from the facts which we have learned, that Lake Michigan 

 has a great influence on the temperature of the surrounding 

 country. The influence of the lake tends to reduce the ex- 

 tremes of temperature. Places near the lake have on the 

 average cooler summers and warmer winters than they would 

 otherwise have. This effect is great enough to be of some 

 importance on the west shore of the lake but of much greater 

 importance on the east shore. 



We are justified in expecting that similar conditions will 

 be found in the vicinity of any large body of water in a tem- 

 perate latitude. In tropical countries, where there is no cold 

 season, conditions are somewhat different, but the same prin- 

 ciples apply. The conditions around Lake Michigan corre- 

 spond exactly with the well-known fact that the western 

 coast of each continent is warmer than the eastern coast in 

 the same latitude. 



