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History of Astronomy by George Forbes
page 118 of 164 (71%)
The discovery of these two satellites is, perhaps, the most
interesting telescopic visual discovery made with the large telescopes
of the last half century; photography having been the means of
discovering all the other new satellites except Jupiter's fifth (in
order of discovery).

[Illustration: JUPITER. From a drawing by E. M. Antoniadi, showing
transit of a satellite's shadow, the belts, and the "great red spot"
(_Monthly Notices_, R. A. S., vol. lix., pl. x.).]

_Jupiter._--Galileo's discovery of Jupiter's satellites was followed
by the discovery of his belts. Zucchi and Torricelli seem to have seen
them. Fontana, in 1633, reported three belts. In 1648 Grimaldi saw but
two, and noticed that they lay parallel to the ecliptic. Dusky spots
were also noticed as transient. Hooke[5] measured the motion of one in
1664. In 1665 Cassini, with a fine telescope, 35-feet focal length,
observed many spots moving from east to west, whence he concluded that
Jupiter rotates on an axis like the earth. He watched an unusually
permanent spot during twenty-nine rotations, and fixed the period at
9h. 56m. Later he inferred that spots near the equator rotate quicker
than those in higher latitudes (the same as Carrington found for the
sun); and W. Herschel confirmed this in 1778-9.

Jupiter's rapid rotation ought, according to Newton's theory, to be
accompanied by a great flattening at the poles. Cassini had noted an
oval form in 1691. This was confirmed by La Hire, Romer, and
Picard. Pound measured the ellipticity = 1/(13.25).

W. Herschel supposed the spots to be masses of cloud in the
atmosphere--an opinion still accepted. Many of them were very
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