Generating Cycles of Products and Prices 31 



Figure 9 

 Secular trends in the index numbers of the production of coal and pig iron in the 

 United States. 



Coal: y = 114.1 + 7.777j + .4131j;-' _ .ooojolx' — .000,8141x', origin at 

 1897; 

 Pig Iron: y = 119.4 + 9.199j + .4110x2— .002,501x3 _ .ooo,7239j<, origin at 

 1897. 



probable are in the neighborhood of eight and eleven or 

 twelve years in length, but in the present paper we shall 

 confine the discussion to the eight-year cycle. When 



