22 nruAL }f inn a AN 



University of i\Iiehigan, dipclosc the fact tliat for 

 latitude 40 degrees and for .Tniie 10. twilight ter- 

 niiiiates at !) : 'M) P. M., while for parallel 4(5, it ter- 

 minates at 10: 29 P. M. A month later the favorable 

 balance is 55 minutes. Combining these surpluses 

 of twilight for all the days of the growing season, 

 the total advantage of parallel 4G over parallel 42 

 is 100 hours, 44 minutes, and of parallel 47 over 

 parallel 42 is 141 hours, IS minutes.^ The pro- 

 censes of growth in plants continue, it is pointed 

 out, during the period of twilight. 



This considerable north and south extension of 

 the State introduces other factors less favorable 

 to agriculture in the northern counties. While the 

 mean annual temperature of Michigan is placed 

 by Schneider at 44 degrees, that of the two southern 

 tiers of counties is approximately 48 degrees, and 

 that of Calumet and Sault Ste. Marie in the ex- 

 treme north but somewhat removed from the in- 

 fluence of the lakes is approximately 39 degrees. 

 The average maximum temperature of the interior 

 portions of the Lower Peninsula is put at 85 to 90 

 degrees, while that of the Upper Peninsula at 

 Marquette is 58.5 degrees (jMay-September, thirty- 

 three years' average). N'evertheless, the record for 

 the highest summer temperature is held by Mar- 

 quette on the south shore of Lake Superior, where, 

 July 15, 1901, the thermometer at the station of 

 the Weather Bureau registered 108 degrees. Winter 

 temperatures in the northern peninsula range about 



' Computations by C. C. Spooner and L. ]\I. Geisin.ir. 



