which they severally belong, as may be seen by the assist-
ance of the telescope.

The Sun is the center round which those six worlds or
planets revolve at different distances therefrom, and in circles
concentric to each other. Each world keeps constantly in
nearly the same tract round the Sun, and continues at the
same time turning round itself, in nearly an upright position,
as a top turns round itself when it is spinning on the ground,
and leans a little sideways.

It is this leaning of the earth (23½ degrees) that occasions
summer and winter, and the different length of days and
nights. If the earth turned round itself in a position per-
pendicular to the plane or level of the circle it moves in
round the Sun, as a top turns round when it stands erect
on the ground, the days and nights would be always of
the same length, twelve hours day and twelve hours night,
and the season would be uniformly the same throughout
the year.

Every time that a planet (our earth for example) turns
round itself, it makes what we call day and night; and
every time it goes entirely round the Sun, it makes what
we call a year, consequently our world turns three hundred
and sixty-five times round itself, in going once round the
Sun. ^*

The names that the ancients gave to those six worlds,
and which are still called by the same names, are Mercury,
Venus, this world that we call ours, Mars, Jupiter, and
Saturn. ¹ They appear larger to the eye than the stars, being
many million miles nearer to our earth than any of the stars

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