But occasionally some large impulse may serve to start a swing and if this impulse is somewhat regularly repeated, it may serve to keep up the rhythmic motion.

True, the lack of coincidence in the impact of various influences which occur accidentally, such as political changes, wars, and the rapid opening of new routes of transportation, would serve to hasten or to retard, perhaps for a time quite to alter, what would otherwise be the rhythm of the cycle.

That there is nevertheless, a noticeable degree of regularity in the recurrence of crises may be due to the presence of one dominating factor.
Alternation of good and poor harvests has always seemed to be favorable to business prosperity.

In America since about 1865, farm products have constituted the larger part of our exports, so that a succession of large harvests has usually acted to stimulate exports (one of the features of a period of prosperity), to give us a larger credit balance in international trade, and to reduce the rate of exchange.

Large harvests of the staple agricultural crops in America have been known to be closely related to the amount of rainfall in the three most important growing months.