160 STATE HORTICULTURAL SOCIETY. 



GO: 18=3.33; lit Manitowoc, for eleven years, as 07:11=6.09; at Grand 

 Haven, for one and a half years, as 34:10=2.1. A similar excess of westerly 

 winds is shown for all the months of the year, except April and May, and 

 especially the month of May. 



In consequence of this prevalence of westerly wind?, the east side of the lake 

 is warmed in winter and cooled in summer. While, therefore, the winter mean 

 at Chicago is 244°, that of New Buffalo, in the same latitude, is 28°. While 

 that of Milwaukee is 22°, that of Grand Haven is 20°. While the winter mean 

 of Fort Howard is 20°, and that of Appleton 19°, the winter mean of Traverse 

 City, farther north than either, is 23A°. In autumn also, the preponderance 

 of westerly winds raises the mean temperature one to two degrees along the 

 south half of the lake shore, and three to four degrees along the northern half 

 of the shore. This is illustrated by the chart which hangs before us, where 

 the red lines pass through localities having the same autumnal means. To 

 the west of the lake region, the lines conform approximately to the parallels 

 of latitude, but over and east of lake Michigan, they bend abruptly northward. 

 The autumnal isotherm of 46°, which passes through Fort Winnebago, bends 

 northward nearly to the extreme point of lake Michigan, a difference of lati- 

 tude of about 185 miles. The isotherm of 47°, which passes through Fort 

 Atkinson, bends northward to the Beaver islands, 192 miles. The isotherm of 

 48° is deflected northward an equal distance. The isotherm of 49° sweeps from 

 Evanston, near Chicago, to the mouth of the Manistee river, a difference of 

 latitude of 152 miles. The isotherm of 50° bends from Kensington, south of 

 Chicago, to Grand Rapids, a difference of latitude of 97 miles. The favorable 

 contrast diminishes in the southern portion of the eastern shore, since in 

 November the cold southwesterly winds either miss the lake entirely, or are 

 held at a lower temperature by mingling with wind which has not traversed 

 the lake. To put the subject in another light, an investigation of the monthly 

 means on the opposite side of the lake, during autumn, shows that the temper- 

 ature attained at Milwaukee, Oct. 15, is not reached at Grand Haven until Oct. 

 20. The Milwaukee temperature of Nov. 15 is only reached at Grand Haven 

 Nov. 23. The Chicago temperature of Sept. 15 is the same as the New Buffalo 

 temperature of Sept. 21. These comparisons show that the warm season is 

 lengthened, on the east side, about six to eight days, in the autumn. In 1865 

 the first killing frost in the Grand Traverse region was Dec. 2; in 1866, Nov. 

 15; in 1867, Nov. 18. 



By a singular and happy exception, in the prevailing direction of the wind, 

 we find that during the month of May, winds from the east of the meridian 

 preponderate. This is shown from the tables again; since at Manitowoc the 

 easterly winds in May are to the westerly as 37:26=1.42; at Milwaukee, as 

 62:24=2.58, and in April as 52:33=1.6; at Chicago, including north winds, 

 which are her lake winds, the ratio of lake and land winds is, in May, as 

 44 :40— 1.1. Now, in May, a lake wind is a chilling influence, except when the 

 thermometer is sinking below the growing temperature for vegetation. It is 

 then an influence which prevents frost. It follows, therefore, that during the 

 mild days of May, the eastern shore of the lake is exempt from the chilling 

 and retarding influence of westerly winds; while, during a cold period, when, 

 as a rule, the wind is westerly, the eastern shore receives the benefit of protec- 

 tion from frost. Thus on the 16th of May, J 868, a destructive frost occurred 

 throughout Illinois, Indiana and Ohio, but did no damage in the Grand Trav- 

 erse region. This unique arrangement seems to have been prompted by a 

 beneficent regard for the interests of early vegetation on our side of the lake. 



