hich come nearest to the sun are vastly surpassed in bulk and
weight by the giant bodies of our system--the stately group of Jupiter
and Saturn, Uranus and Neptune.

[Illustration: Fig. 33.--The Orbits of the Four Giant Planets.]

These giant planets enjoy the sun's guidance equally with their weaker
brethren. In the diagram on this page (Fig. 33) parts of the orbits of
the great outer planets are represented. The sun, as before, presides at
the centre, but the inner planets would on this scale be so close to the
sun that it is only possible to represent the orbit of Mars. After the
orbit of Mars comes a considerable interval, not, however, devoid of
planetary activity, and then follow the orbits of Jupiter and Saturn;
further still, we have Uranus, a great globe on the verge of unassisted
vision; and, lastly, the whole system is bounded by the grand orbit of
Neptune--a planet of which we shall have a marvellous story to narrate.

The various circles in Fig. 34 show the apparent sizes of the sun as
seen from the different planets. Taking the circle corresponding to the
earth to represent the amount of heat and light which the earth derives
from the sun then the other circles indicate the heat and the light
enjoyed by the corresponding planets. The next outer planet to the earth
is Mars, whose share of solar blessings is not so very inferior to that
of the earth; but we fail to see how bodies so remote as Jupiter or
Saturn can enjoy climates at all comparable with those of the planets
which are more favourably situated.

[Illustration: Fig. 34.--Comparative Apparent Size of the Sun as seen
from the Various Planets.]

Fig. 35 shows a picture of the whole family of planets surrounding the
sun--represented on the same scale, so as to exhibit their comparative
sizes. Measured by bulk, Jupiter is more than 1,200 times as great as
the earth, so that it would take at least 1,200 earths rolled into one
to form a globe equal to the globe of Jupiter. Measured by weight, the
disparity between the earth and Jupiter, though still enormous, is not
quite so great; but this is a matter to be discussed more fully in a
later chapter.

[Illustration: Fig. 35.--Comparative Sizes of the Planets.]

Even in this preliminary survey of the solar system we must not omit to
refer to the planets which attract our attention, not by their bulk, but
by their multitude. In the ample zone bounded on the inside by the orbit
of Mars and on the outs