The Eaton Democrat. (Eaton, Ohio) 1875-1903, 1877-10-18
Predictions In Regard to the Moons
of Mars.

Richard A. Proctor, in communica-
tion to the London Times, says: {" think
science must claim the prediction of the
discovery of Martian moons as well as
the discovery itself; the prediction was
made by men of science, though not in
what is now regarded as the true
scientific spirit. When Galileo an
nounced the discovery of the Jovian
satellites, Kepler, after consulting him,
said, l please myself with the thought
that you will discover two moons attend
ing on Mars and many attending on
Saturn Such at least is my recollec-
tions of Kepler's words. In works on
astronomy, published in the seventeenth
century, the idea was generally advanced
that Mars must have two satellites, and
if 1 remember rightly, the younger
Cassini, in his clemens d'Astronomie
"a work which Voltaire must, and
Arbuthnot may have seen), urged from
considerations of analogy that Mars
should have two moons, and explained
how these might have escaped observa-
ton by being very close to their primary.
The view was certainly urged either by
J. Cassini or his cousin Maraldi. The
elder Cassini had disposed of an argu-
ment from analogy advanced by Huy-
ghens, who, when he had discovered
Titan, said there could be no other
moons. Cassini discovered. four more
Saturnian moons. Yet these arguments
from analogy long remained in favor.
What Bacon said of astrological predic-
tions was (and is) true of them Men
mark when they hit. and never mark
when they miss The arguments from
analogy were regarded by many as
equivalent to scientific demonstrations.
Even Newton, after showing that Jupi-
ter is denser than Saturn, aud the earth
than Jupiter, goes to say (on the strength
of analogy only, I'VE are not to doubt
that the matter of Mercury is more dense
than the matter of the earth,' which
chancesto be true, though the analogy is
unsound. Both Uranus and Neptune
are denser than Saturn, whereas, accord
ing to Newton's argument, they should
be rarer. There are good reasons for
believing that Swift's idea about the
Laputan discovery of Martian satellites
was elaborated by Arbuthnot. As
Professor De Morgan points out in his
" Budget of Paradoxes," we can not
credit man who could not understand
leap year (Swift had always supposed,
he tells Stella, that one year in three
was leap year) with the correct invention
of Martian satellites according to Kep-
ler's third law. Your readers take it for
granted that the discovery OF the moons
of Mars is altogether new. Even now
that these bodies are known, there are
not ten telescopes in the world that can
show them. They will be lost to view
after October, even in the Washington
refractOr, the largest yet mounted.
They may be visible again during few
weeks in autumn, 1879; but after that
no telescope will show them until 1892.
There was bare possibility that in 1S45
they might have been detected had
diligent search been made; but up to
that date men had not opened their
telescope eyes sufficiently to see these
tiny orbs. l have mentioned the
peculiarities of the inner satellites in
moving from west to east across the
Martian sky. The outer also has it
peculiarities. For instance, parodoxical
though it may seem, this moon, which
circuits Mars in thirty and one-quarter
hours, and in that time circuits also the
stellar heavens, takes about twice that
time in passing from the eastern to the
western horizon. In other words, the
lunar day is about four times as long as
the lunar month.
" In paper which appeared in
weekly contemporary shortly before the
details of the discovery arrived, l esti-
mated the diameter of the outer satellite
as most probably not exceeding ten
miles. Professor Newcomb of the Wash
ington Observatory, in a communication
to the New York Tribune, says that the
diameter can not be much over ten
miles. and NAV be less."