138 IOWA DEPARTMENT OF AGRICULTURE. 



the larger part of Iowa is within the isothermal belt 15" to 20^ . These lines 

 run northwestward through Wisconsin, northern Michigan, Ontario, north- 

 ern New York, Vermont, New Hampshire and Maine. The midwinter 

 temperature corresponds to that of the vicinity of Montreal, while the sum- 

 mers are as warm as in Washington, D. C, and Richmond, Va; The 

 winters, however, are shorter than in the same latitude in the Atlantic 

 states. The transition from winter to summer is usually quite rapid, the 

 average increase in temperature in April being more than half a degree 

 daily. The daily mean of April is 17° higher than that of March, and May 

 averages 11° per day higher than April. The season of seeding and plant- 

 ing is 8 to 12 days earlier than in the 'eastern states. The autumns are 

 usually drier and warmer in Iowa than in the coastal regions on the same 

 parallels. The average duration of summer temperature, the daily means 

 ranging from 65° to 75°, is about four months. The average duration of 

 winter, or the period having a mean below 30°, is about three and a half 

 months. 



The highest temperature registered in Iowa by a standard thermometer 

 was 113°, at Sigourney in July, 1901. The lowest temperature recorded 

 was 43° below zero, at Cresco, in January, 18S8. These records indicate 

 the remarkable range of 156° from minimum to maximum temperature. 

 These extremes of heat and cold are rendered more endurable to man and 

 beast by the prevalent dryness of the air at the time of their occurrence. In 

 the humid air of insular regions such extremes would be intolerable. In 

 this connection it may be stated that both heat and cold are important fac- 

 tors in the production of the great crops for which this section is noted. The 

 myriad plowshares of the frost penetrate the earth to great depths, pulver- 

 izing the clods and preparing the soil to respond to the quickening influence 

 of the gentle rains of spring and the almost tropical heat of summer. This 

 is not an ideal climate for invalids, ^ who need equable temperature, but na 

 country is better adapted to develop hardy, stalwart and brainy people than 

 this valley, where the rigors of winter incite men to a strenuous life. Some 

 adverse conditions seem to be necessary to develop hardiness and vigor in 

 plants, animals and mankind. The best types of all races have been reared 

 about midway between the tropics and the Arctic zones. 



The following table shows the monthly and annual mean temperatures 

 for the state, for the thirteen-year period, 1890 to 1902, inclusive. This is 

 followed by a table showing the averages by districts and sections, and also 

 for the state at large, for all the years of record . A slight difference will be 

 noted in the state averages for the thirteen-year period, as compared with 

 the means shown in the latter table: 



