#16a.     Discovery of the Sunspot Cycle

Excerpts from Solar Observations During 1843 by Heinrich Schwabe, (Astronomische Nachrichten, vol. 20., no. 495, 1843)

From my earlier observations, which I have reported every year in this journal, it appears that there is a certain periodicity in the appearance of sunspots and this theory seems more and more probable from the results of this year. ...I should like now to add a complete report of all my observations of sunspots up to the present, in which I have indicated the number of days of observation and the days when there were no spots to be seen, as well as the number of groups.