The diameter of these
satellites is really less than the distance from High Park, on the
west of Toronto, to Woodbine race course, on the east of the city. No
wonder these minute objects--seldom, if ever, nearer to us than about
forty millions of miles--are difficult to see at all. Newcomb and
Holden tell us that they are invisible save at the sixteen year
periods referred to, when it happens that the earth and Mars, in their
respective orbits, approach each other more nearly than at any other
time. But once discovered, the rule held good even in the case of the
satellites of Mars. Pratt has seen Deimos, the outermost moon, with an
eight and one-seventh inch telescope; Erek has seen it with a seven
and one-third inch achromatic; Trouvellot, the innermost one, with a
six and three-tenths glass, while Common believes that any one who can
make out Enceladus, one of Saturn's smallest moons, can see those of
Mars by hiding the planet at or near the elongations, and that even
our own moonlight does not prevent the observations being made.
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