FOURTH ANNUAL YEAR BOOK — PART II. 137 



by ano.her; and this oscillation from dry to wet, or vice veisa, may occur 

 qaickly, or it may run throujjh two, three or four years. In the biennial 

 period of 1901-1902 there was a very rapid swing of the pendulum from 

 excessive heat and drought to the opposite extreme of cold and wet weather. 

 And in respect to quality and commercial value the soil output of 1901 was 

 much better than that of 1902. Generally, it may be said, the predominant 

 influence in this valley in midsummer is much stronger toward prolonga- 

 tion of wet weather periods than the dry weather type. A considerable 

 portion of the summer rainfall comes in form of local showers, which irri- 

 gate narrow belts and short distances; and it not infrequently happens that 

 a portion of a single county may be well watered, while other parts are 

 greatly in need of moisture. 



Though subject to very considerable fluctuations in the amount of rain- 

 fall in the crop season, there is a measure of compensation in the deep, rich 

 and porous soil of this state, which has produced fairly good crops in the 

 driest or wettest seasons. In the worst season ever experienced in this por- 

 tion of the great valley there has been no near approach to a famine. The 

 most severe drought within the past fifty years occurred in 1894, and yet this 

 state produced in that year 256,OCO,000 bushels of cereals, and sufficient 

 other soil products to swell the total value to over $121,000,000. The su- 

 perior quality of Iowa soil was noted by the late Prof. T. S. Parvin, who in a 

 contribution to the American Journal of Science, Vol. XIII, said:/ "In 

 1854 occurred the great drought in this and the western states generally; but 

 owing to the porous nature of our soil the crops with us turned out much 

 better than in the states east of the Mississippi. In 1856 the season was also 

 very dry, the total quantity of rain in the summer months being only 6.78 

 inches, or 10.20 below the summer mean. The crops were, notwithstand- 

 ing, more than an average yield, both of corn and small grain; and the 

 three or four dry seasons we have had abundantly prove that the soil and 

 climate of Iowa are unsurpassed on the continent for farming purposes." 



TEMPERATURE. 



On the climatological map published by the United States Weather 

 Bureau , Iowa is situated in the isothermal belt wherein the mean annual 

 temperature ranges from 45"^ to 50®. The lines inclosing this belt run 

 nearly parallel from the Missouri valley to the Atlantic coast, and embrace 

 a large part of the territory between 41° and 44° north latitude. The mean 

 annual temperature of this state is 47.5°. By sections the mean tempera- 

 tures are as follows: Northern section, 45 7°; central section, 47.3°; south- 

 ern section, 50°. The highest yearly mean at any station is 51.7° , as shown 

 by records of the Weatner Bureau station at Keokuk; the lowest is 43.2°, 

 according to records of voluntary stations at Osage and Cresco. F'rom the 

 south line of the state to the Minnesota boundary the temperature gradient is 

 quite uniform, making due allowance for differences in altitude of stations 



In this part of the Mississippi valley the summers are warmer and the 

 winters colder than on the same parallels near the Atlantic coast. In July 

 the 75° isotherm passes through the southern half of Iowa, dips southeast- 

 ward below Cincinnati, passing between Baltimore and Philade'phia. The 

 mean maximum of the state for July is 85°, and the midsummer tempera- 

 ture is about as high as that of Virginia and North Carolina. In January 



