Generating Cycles of Products and Prices 29 



prices. The leading crops upon which the computation 

 was based supplied 70 per cent of the total value of 

 American crops in 1919 and are therefore sufficiently 

 representative of the yield and prices of fanii products. 

 Next to the farms, according to the above figures, the 

 mines furnish the most important source of materials for 

 manufactures. The farms and the mines together 

 supplied, in 1900,' 94.6 per cent of the value of the raw 

 materials used in American factories. Does the pro- 

 duction of minerals move in cycles? 



The most important minerals for the use of manufac- 

 tures and transportation are coal and iron, and in our 

 further inquiry these two minerals will be regarded as 

 being representative of the products of the mines just 

 as the six crops — corn, wheat, oats, hay, cotton, and 

 potatoes — were treated as being representative of the 

 products of the farm. 



In preparing the statistics of the production of coal 

 and pig iron with a \dew to ascertaining whether there is 

 any periodicity in their production, the procedure was 

 smiilar to that which was followed in the case of the 

 yield of the crops. The raw figures ^ of production were 

 first reduced to index numbers in which the mean pro- 

 duction for 1890-99 was placed as equal to 100. The 

 graphs of the index numbers of production are given in 

 Figure 9. Because of the enonnous and irregular in- 

 crease in the production of both coal and iron in the in- 

 terval under investigation, 1881-1913, the description 

 of the secular trends by means of single equations 

 requires the use of a slightly more complex curve than 



* The figures were taken from the Slalislical Abstract of the United 

 States, 1915, pp. 689, 690. 



