Page 509 - 89 history of astronomy_opt

planets rotate in about ten hours (Uranus
and Neptune being still indeterminate).
The general surface of Mars is a deep
yellow; but there are dark grey or greenish
patches. Sir John Herschel was the first to
attribute the ruddy colour of Mars to its
soil rather than to its atmosphere.
The observations of that keen-sighted ob-
server Dawes led to the first good map of
509