COSMOS, VOL. II - World eBook Library

DISCOVERIES IN THE CELESTIAL SPACES. 707
possess only very obscure and discrepant data on this subject.
It is probable that he recognised the solar spots in April
1611, for he showed them publicly at Rome in Cardinal Bandini's
garden on the Quirinal, in the months of April and May
of that year. Hariot, to whom Baron Zach ascribes the discovery
of the sun's spots, (16th of January, 1610), certainly saw
three of them on the 8th of December, 1610, and noted them
down in a register
of observations but he was ;
ignorant that
they were solar spots ; thus, too, Flamstead, on the 23rd of
December, 1690, and Tobias Mayer, on the 25th of Septem-
ber, 1756, did not recognise Uranus as a planet when it
passed across the field of their telescope. Hariot first observed
the solar spots on the 1st of December, 1611, five months,
therefore, after Fabricius had published his discovery.
Galileo
had made the observation that the
"
solar spots, many of
which are larger than the Mediterranean, or even than Africa
and Asia," form a definite zone on the sun's disk. He occasionally
noticed the same spots return, and he was convinced
that they belonged to the sun itself. Their differences of
dimension in the centre of the sun, and, when they disappeared
on the sun's edge, especially attracted his attention,
but still I find nothing in his second remarkable letter of the
14th of August, 1612, to Marcus Welser, that would indicate
his having observed an inequality in the ash-coloured margin
on both sides of the black nucleus when approaching the sun's
edge (Alexander Wilson's accurate observation in 1773). The
Canon Tarde, in 1620, and Malapertus in 1633, ascribed all
obscurations of the sun to small cosmical bodies revolving
around it and intercepting its light, and named the Bourbon
and Austrian stars* (Borbonia et Austriaca Sidera). Fabricius
recognised, like Galileo, that the spots belonged to the
sun itself;f he also noticed that the spots he had seen vanish
all re-appear; and the observation of these phenomena taught
him the rotation of the sun, which had already been conjectured
by Kepler before the discovery of the solar spots. The
most accurate determinations of the period of rotation were,
however, made in 1630, by the diligent Scheiner. Since the
strongest light ever produced by man, Drummond's incan-
* Delambe, Hist, de VAstronomie moderne, t. i. p. 690.
f The same opinion is expressed in Galileo's Letters to Prince Cesi
(May 25, 1612); Venturi, P.i. p. 172.
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