138 



ELEMENTS OF GENERAL SCIENCE 



In order to secure a clear idea of the conditions it is necessary 

 to know the mean temperatures at the places compared. 



The accompanying table gives the mean monthly tempera- 

 tures, as ascertained by the United States Weather Bureau, 

 for three cities which are located on the shores of Lake 

 Michigan and in the adjacent country. These averages have 

 been made up from a study of temperature observations ex- 

 tending over many years. Examination of the data will show 

 that the mean monthly temperatures are definitely lower dur- 

 ing the summer months at the lake cities than at inland 

 points in approximately the same latitude. It appears, there- 

 fore, that there is foundation for the belief that the shores 

 of the lakes offer more pleasant summer temperatures than 

 may be found at other places. The same conclusions would 

 be reached if other lake cities were compared with places 

 remote from the lakes. 



MEAN MONTHLY TEMPERATURES 



155. The lake breeze. Those who live near the shores of 

 any of the Great Lakes are accustomed to attribute much of 

 their freedom from great heat to the lake breeze (fig. 73). 

 This breeze frequently blows on hot days and gives relief 

 from heat. Often the morning is quite warm, and the heat 

 increases rapidly, as the sun gets higher in the heavens, until 

 about ten o'clock, when a cool breeze begins to blow from the 

 lake and the temperature becomes pleasant again. The breeze 

 may continue until about four o'clock in the afternoon or 

 later. Of course, the effect of the breeze is most pronounced 

 near the lake, and it does not extend many miles inland. The 

 same phenomena are observed on ocean shores. 



