78 



Generating Economic Cycles 



Is the rainfall itself subject to law? In the lower part 

 of Figure 21 an eight-year cycle is fitted to the annual 

 rainfall data, and we find that the maxima occur at 

 1866, 1874, 1882, 1890, 1898, 1906— which makes the 

 Prescott rainfall, during this interval, synchronous 



Figure 21. Cycles in the rainfall and in the growth of pines near Prescott, Arizona. 

 Equation to the rainfall cycle, y = 16.9 + 3.2 sin (3.|£.°f + 127° 12'), origin at 1867. 



with the crop cycles in the United States, in the United 

 Kingdom, and in France. Gratifying as this result is, 

 I should not attach importance to it — because of the 

 meteorological record being made up of observations at 

 two different stations in a country in which the rainfall 

 is notoriously variable from station to station — but 

 for its relation to what is about to be described. 



Flagstaff, in Arizona, is about 67 miles north of 

 Prescott. From the magnificent pine forests about 

 Flagstaff Professor Douglass was able to obtain cuttings 

 from trees which supplied him with a continuous history 



