lso
C. J. Monro's useful indications in _Nature_, vol. vii., p. 241.]

[Footnote 959: _Dynamik des Himmels_, p. 40.]

[Footnote 960: Gould's _Astr. Jour._, vol. iii., p. 138.]

[Footnote 961: _Wash. Obs._ for 1875, vol. xxii., App. ii.]

[Footnote 962: _Comptes Rendus_, t. cxiii., p. 669; _Annuaire_, Paris,
1892.]

[Footnote 963: Newcomb, _Pop. Astr._ (4th ed.), p. 101.]

[Footnote 964: Sir W. Thomson, _Report Brit. Ass._, 1876, p. 12.]

CHAPTER VIII

_PLANETS AND SATELLITES_--(_continued_)

"The analogy between Mars and the earth is perhaps by far the greatest
in the whole solar system." So Herschel wrote in 1783,[965] and so we
may safely say to-day, after six score further years of scrutiny. The
circumstance lends a particular interest to inquiries into the physical
habitudes of our exterior planetary neighbour.

Fontana first caught glimpses, at Naples in 1636 and 1638,[966] of dusky
stains on the ruddy disc of Mars. They were next seen by Hooke and
Cassini in 1666, and this time with sufficient distinctness to serve as
indexes to the planet's rotation, determined by the latter as taking
place in a period of twenty-four hours forty minutes.[967] Increased
confidence was given to this result through Maraldi's precise
verification of it in 1719.[968] Among the spots observed by him, he
distinguished two as stable in position, though variable in size. They
were of a peculiar character, showing as bright patches round the poles,
and had already been noticed during sixty years back. A current
conjecture of their snowy nature obtained validity when Herschel
connected their fluctuations in extent with the progress of the Martian
seasons. The inference of frozen precipitations could scarcely be
resisted when once it was clearly perceived that the shining polar zones
did actually by turns diminish and grow with the alternations of summer
and winter in the corresponding hemisphere.

This, it may be said, was the opening of our acquaintance with the state
of things prevailing on the surface of Mars. It was accompanied by a
steady assertion, on Herschel's part, of permanence in the dark
markings, notwithstanding partial obscurations by clouds and vapours
floating in a "considerable but moderate atmosphere." Hence the presumed
inhabitants of the planet were inferred to "probably enjoy a situation
in many respects similar to ours."[969]

Schroeter, on the othe