Four years after the death of Herschel, an apothecary in the little German town of Dessau procured a small telescope, with which he began to observe the Sun. The name of this apothecary was _Samuel Heinrich Schwabe_ (1789-1875). In 1826 he commenced to observe the spots on the Sun’s disc, counting them from day to day, more for self-amusement than from any hope of discovery; for previous astronomers had agreed that no law regulated the number of the sun-spots. Every clear day Schwabe pointed his telescope at the Sun and took his record of the spots; this he continued for forty-three years, until within a few years of his death on April 11, 1875. As early as 1843 Schwabe hinted that a possible period of ten years regulated the distribution of the spots on the Sun, but no attention was given to his idea. In 1851, however, the result of his twenty-six years of observation was published in Humboldt’s ‘Cosmos,’ and Schwabe was able to show that the spots increased and decreased in a period of about ten years. Astronomers at once recognised the importance of Schwabe’s work, and in 1857 he was rewarded by the Gold Medal of the Royal Astronomical Society of London. _Rudolf Wolf_ (1813-1892) of the Zürich Observatory now undertook to search through the records of sun-spot observation, from the days of Galileo and Scheiner, to find traces of the solar cycle discovered by Schwabe. He was successful, and was enabled to correct Schwabe’s estimate of the length of the period, fixing it as on the average 11·11 years. Additional interest, however, was given to Schwabe’s and Wolf’s investigations by the remarkable discoveries which followed. In September 1851 _John Lamont_ (1805-1879), a Scottish astronomer,—born at Braemar in Aberdeenshire, but employed as director of the Munich Observatory,—after searching through the magnetic records collected at Göttingen and Munich, discovered that the magnetic variations indicated a period of 10⅓ years. Soon after this Sir _Edward Sabine_ (1788-1883), the English physicist, from a discussion of an entirely different set of observations, independently demonstrated the same thing, proving conclusively that once in about ten years magnetic disturbances reached their height of violence; and Sabine was not slow to notice the correspondence between the magnetic period and the sun-spot period. In the same year (1852) Wolf and _Alfred Gautier_ (1793-1881) independently made the same discovery, which had thus been made by four separate investigators.