FOURTH ANNUAL YEAR BOOK — PART II. 143 



moderate in force in comparison with the tropical cyclones or hurricanes that 

 occasionally devastate portions of the Gulf and Atlantic coast .<!- The most 

 severe storms that visit this region are of the minor or local class of disturb- 

 ances, and their destructive effects are usually limited to narrow tracks and 

 small areas. The earth is watered and made fruitful by the expenditure of 

 tremendous energy in the operation of nature's rain making machinery, and 

 the most d2structive storms are incidental ills resulting from conditions which 

 promote the general good. Hailstorms, windsqualls, thunderstorms and 

 tornadoes are exceptional products of the benign elements of heat and 

 moisture which have made this valley a paradise of abundance. There are 

 regions oE wide extent, which enjoy well nigh perfect immunity from these 

 severe storms, but they are mostly deserts or arid sections which must be 

 irrigated to yield even a scanty support to their inhabitants. 



In Iowa the heaviest damage to crops has been caused by hail, and light- 

 ning is the element that causes greatest destruction of human life, farm 

 animals and buildings. Wind squalls have wrought considerable destruction 

 to farm buildings, windmills and frail structures in exposed localities. 

 Tornadoes have caused more general alarm among people at home and 

 abroad, but in reality they have been relatively infrequent, and have caused 

 less real damage than has resulted from ordinary thunderstorms. The area 

 devastated by tornadoes in this state is quite insignificant in comparison with 

 the whole state; in fact, it may be stated that not exceeding one half of one 

 per cent of the entire surface of the state has been swept over by tornadoes 

 within the past half century. There have been scores of windstorms that 

 were miscalled tornadoes in sensational reports, but the real, deadly tornado 

 is an infrequent visitor, and when one comes its path is very narrow. There 

 has been a vast deal of exaggeration in relation to that class of storms. 



Gen. A. W. Greeley, chief signal officer of the United States army, in his 

 book on American Weather, said that about three thousand persons in the 

 United States have been killed by tornadoes, and the loss of life has been 

 greatest in the following states, in the relative order named: Missouri, 

 Mississippi, Iowa, Illinois, Minnesota, Wisconsin and Ohio. In his annual 

 report for l&i:0. General Greeley gave the following estimate of the total area 

 visited annually by violent storms of all classes: In Alabama one square 

 mile of limited destruction to 8,866 square miles of area; Arkansas, 1 to 

 14,418; Georgia, 1 to 6,696; Illinois, 1 to 8 162; Indiana, 1 to 6,210; lov/a, 1 to 

 7,164; Kansas, 1 to 9,720; Missouri, 1 to 5,336; Ohio, 1 to 4,554; Wisconsin, 

 1 to 12,042 miles. 



The mean velocity of the wind over this state is about the average for the 

 United States eastward of the one hundredth meridian. The average hourly 

 movement is seven to eight miles. In recent years the force of the wind has 

 been measurably broken, or modified, by artificial timber belts, hedges, etc. 

 The prevailing winds in summer are southerly, and westerly at other seasons. 



IS THE CLIMATE PERMANENT? 



All records of weather observations in this state for the past fifty years 

 give an afl&rmative answer to the above inquiry, though there are some who 

 still regard it as an open question. The chief value of records covering 

 considerable periods is that they illustrate not only the seasonal variability 

 but also the permanent conditions of climate. There is as much weight of 

 testimony to sustain the theory that the climate is becoming wetter and 



