Before Milankovic, French mathematician Joseph Adhemar (1797–1862) published his book Revolutions of the Sea in 1842. In it, he suggested ice ages occur in 22,000-year cycles that matched the precession of the equinoxes. Scottish geologist James Croll (1821–1890) later elaborated on this theory. However, scientists did not know enough about the history of ice ages to compare this theory with actual data, and so the hypothesis languished for another century.