The Mechanism of Cycles 109 



the yield per acre of the crops and of the production of 

 pig-iron; in columns 3 and 6, the values of the linear 

 secular trends are given; and in columns 4 and 7, the 

 deviations of the cyclical movement from the secular 

 trend are recorded. These last deviations are the ma- 

 terial for calculating the connection between the cycles 

 of the yield per acre of the crops and the cycles of the 

 production of pig-iron. 



If the deviations of the cycles from their respective 

 secular trends are correlated, the coefficient of correla- 

 tion reaches the value, r = .625, but we must not be 

 content to assume that even this relatively high co- 

 efficient represents the full degree of the relation be- 

 tween the cyclical movement of the crops and the 

 cyclical movement of the activity of industry as that 

 activity is typified in the production of pig-iron. It is 

 quite likely that the good or bad crops may produce 

 their maximum effect at a considerable interval after 

 the period in which the crops are actually harvested. 

 Time is required for the changing productivity of 

 crops to work out its maximum effect, and this causes 

 a lag in the adjustment of the cycles of the activity of 

 industry to the cycles of the yield of the crops. We 

 must therefore measure the amount of the lag. 



If instead of correlating the cycles of the yield of the 

 crops and of the production of pig-iron for correspond- 

 ing years, we correlate them for lags of various intervals, 

 we shall find it possible to determine the lag that will 

 give the maximum coefficient of correlation, and this 

 particular value of the lag we may then regard as the 



