Jevons' analysis, 2.— Other theories of cyclical relations: Moore, 4; Huntington, 5.— The solar cycle, 7.— Correlation between solar and economic cycles, 9.—Changes in solar cycles and economic series, 10. — Variation in latitude of sunspots and index of physical production, 11.— Correlation between solar cycles and non-agricultural series, 13. — The explanation of this relation, 23.— Theories: Pigou, 26.— Hexter, 28.— Vallot, 29.— Effect of ultraviolet rays, 31. — The electrical hypothesis, 33.— The volcanic dust theory, 35.— Correlation between temperature and business activity, 38.— Correlation between monthly figures of the "preferred solar constant, " business activity, and solar radiation, 42.— The last depression and the psychological theory, 45. — Monthly variations in speculation and solar activity for 1929, 46. — Sunspots in the central zone and speculation, 49. — Conclusion, 51.