Rudolf Wolf

Johann Rudolf Wolf (7 July 1816 – 6 December 1893) was a Swiss astronomer and mathematician best known for his research on sunspots. Wolf was born in Fällanden, near Zurich. He studied at the universities of Zurich, Vienna, and Berlin. Encke was one of his teachers. Wolf became professor of astronomy at the University of Bern in 1844 and director of the Bern Observatory in 1847. In 1855 he accepted a chair of astronomy at both the University of Zurich and the Federal Institute of Technology in Zurich.

Wolf was greatly impressed by the discovery of the sunspot cycle by Heinrich Schwabe and he not only carried out his own observations, but he collected all the available data on sunspot activity back as far as 1610 and calculated a period for the cycle of 11.1 years. In 1848 he devised a way of quantifying sunspot activity. The Wolf number, as it is now called, remains in use. In 1852 Wolf was one of four people who discovered the link between the cycle and geomagnetic activity on Earth. Notices of Wolf's discovery appeared in:
 * The three other astronomers who observed a relation between the solar cycle and magnetic declination on Earth were:
 * Johann von Lamont (1805–1879) of Scotland and Germany:
 * Edward Sabine (1788–1883) of Ireland: From p. 103: " … I have had the satisfaction of finding that the observations [of magnetic declination] of these years [i.e., 1846–1848] confirm … the existence of a periodical variation, which … corresponds precisely both in period and epoch, with the variation in the frequency and magnitude of the solar spots, recently announced by M. Schwabe … "
 * Jean-Alfred Gautier (1793–1881) of Switzerland:  On pp. 189–190, after discussing Schwabe's discovery of the solar cycle, Gautier presents Lamont's findings on the relation between the solar cycle and the periodic variations in the magnetic declination.  Gautier mentions that the Austrian astronomer Augustin Reslhuber (1808–1875) confirmed Lamont's findings.  (Reslhuber's confirmation appeared in:  )
 * Edward Sabine (1788–1883) of Ireland: From p. 103: " … I have had the satisfaction of finding that the observations [of magnetic declination] of these years [i.e., 1846–1848] confirm … the existence of a periodical variation, which … corresponds precisely both in period and epoch, with the variation in the frequency and magnitude of the solar spots, recently announced by M. Schwabe … "
 * Jean-Alfred Gautier (1793–1881) of Switzerland:  On pp. 189–190, after discussing Schwabe's discovery of the solar cycle, Gautier presents Lamont's findings on the relation between the solar cycle and the periodic variations in the magnetic declination.  Gautier mentions that the Austrian astronomer Augustin Reslhuber (1808–1875) confirmed Lamont's findings.  (Reslhuber's confirmation appeared in:  )

Around 1850, to study the laws of probability, Wolf performed a Buffon's needle experiment, dropping a needle on a plate 5000 times to verify the value of π, a precursor to the Monte Carlo method.