Surrey, established the remarkable fact that, while the rotation
period in the highest latitudes, 50 degrees, where spots are seen, is
twenty-seven-and-a-half days, near the equator the period is only
twenty-five days. His splendid volume of observations of the sun led
to much new information about the average distribution of spots at
different epochs.

Schwabe, of Dessau, began in 1826 to study the solar surface, and,
after many years of work, arrived at a law of frequency which has been
more fruitful of results than any discovery in solar physics.[5] In
1843 he announced a decennial period of maxima and minima of sun-spot
displays. In 1851 it was generally accepted, and, although a period of
eleven years has been found to be more exact, all later observations,
besides the earlier ones which have been hunted up for the purpose, go
to establish a true periodicity in the number of sun-spots. But quite
lately Schuster[6] has given reasons for admitting a number of
co-existent periods, of which the eleven-year period was predominant
in the nineteenth century.

In 1851 Lament, a Scotchman at Munich, found a decennial period in the
daily range of magnetic declination. In 1852 Sir Edward Sabine
announced a similar period in the number of "magnetic storms"
affecting all of the three magnetic elements--declination, dip, and
intensity. Australian and Canadian observations both showed the
decennial period in all three elements. Wolf, of Zurich, and Gauthier,
of Geneva, each independently arrived at the same conclusion.

It took many years before this coincidence was accepted as certainly
more than an accident by the old-fashioned astronomers, who want rigid
proof for every new theory. But the last doubts have long vanished,