THE CLIMATE OF THE LAKE REGION. 217 



Grand Haven March 15 is equal to that of Milwaukee 

 March 21; that of Grand Haven April 15 is equal to that 

 of Milwaukee April 24; that of Grand Haven May 15 is 

 equal to that of Milwaukee May 28. These are not sin- 

 gle instances, but comparisons of results of many years 

 of accurate instrumental observation. They show that in 

 May Grand Haven is thirteen days in advance of Milwau- 

 kee. Add the thirteen days of growing weather gained 

 in spring to the five days gained in October, and we per- 

 ceive that the growing season is eighteen days longer at 

 Grand Haven than at Milwaukee. Every practical culti- 

 vator knows that eighteen days often make all the differ- 

 ence between a crop well ripened and perfect and a crop 

 immature and savorless, if not ruined by an untimely 

 freeze. 



This contrast is the same in kind as exists along the 

 whole length of the two shores; but we find it qualified 

 by two influences. First, the northern portion of the 

 western shore receives a warming influence from northerly 

 winds approaching over Green Bay ; but, at the same 

 time, the greater expanse of water passed over by westerly 

 and southwesterly winds approaching the Grand Traverse 

 region imparts to that region a greater relative influence 

 than is felt by the Grand Haven region. Secondly, the 

 southern portion of the Michigan shore of the lake is 

 exposed to the unmitigated sweep of southwest winds, 

 which, in the northwestern states, are often the coldest 

 of all; but, on the contrary, this region receives north- 

 westerly, and even north, winds which have swept over a 

 vast expanse of lake surface. 



I have thus far referred only to annual and seasonal 

 means. The longer the period embraced in the compu- 



