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STATE BOARD OF AGRICULTURE. 



sufficient to produce a relative luuiiidity of but 50 per cent when the 

 air temperature is increased to G0° F. 



Of the four factors which control climate only the last two need to 

 be mentioned here in their relation to humidity, because neither the 

 range of latitude or altitude found in Michigan is sufficient to ap- 

 preciably change the humidity. But the presence of the large water 

 surfaces of the Great Lakes is an important factor in influencing the 

 humidity, because such surfaces are constantly evaporating Avater into 

 the atmosphere. The following table Avill serve to show the effect of the 

 Great Lakes on relative humidity: 



TABLE VIII.— RELATIVE HUMIDITY AT LANSING, MICH., AND BISMARCK, N. D. AT 



7 P. M., BY jSIONTHS AND FOR THE YEAR. 



Part of the difference in relative humidity between the two stations 

 in the table is probably due to the fact that Bismarck, N. D., is some 

 distance from the normal storm path, while Lansing, Michigan is more 

 directly in the region most frequently traversed by "highs" and "lows." 

 An increase in cloudiness and rainfall, brought about by the passage 

 of low pressure areas, also causes an increase in relative humidity. 



OTHER PHENOMENA. 



There is yet to be considered the occurrence of other atmospheric 

 phenomena such as hail, frost, tornadoes, etc. These are more or less 

 destructive to farm crops and their discussion will properly fall in what 

 is to follow. But a word should be said as to their distribution and 

 frequency over the state before the subject of the relation between the 

 climate of Michigan and agriculture is taken up. 



Hail is attendant upon heavy thunderstorms. It is very local in char- 

 acter, covering only small areas in any particular storm. On the average 

 two hailstorms per year occur at Lansing, which may be considered a 

 typical station for Michigan, but the number is less near the lake shores. 



Frosts occur each fall and spring, the dates being largely influenced 

 by the first three factors, influencing climate, i. e., latitude, altitude, and 

 proximity of the lakes. The fourth factor should also be considered but 

 somewhat modified. Latitude of course is an important factor in deter- 

 mining how late in the spring and early in the fall killing frosts are 

 liable to occur. In the interior of the upper peninsula the weather re- 

 mains cold until early summer and the period of warm weather is short, 

 while in the extreme southern portion of the state it is much warmer. 

 A table is appended giving the dates of frost and the length of the grow- 

 ing season at many stations in the state. From this table the following 

 is extracted to illustrate the matter of the effect of latitude on dates of 

 frost : 



