en the normal
duration of life, neither the travelers who set out for the Sun, nor
their children, nor their grandchildren, would arrive there: only the
seventh generation would reach the goal, and only the fourteenth could
bring us back news of it.

Children often cry for the Moon. If one of these inquisitive little
beings could stretch out its arms to touch the Sun, and burn its fingers
there, it would not feel the burn for one hundred and sixty-seven years
(when it would no longer be an infant), for the nervous impulse of
sensation can only be transmitted from the ends of the fingers to the
brain at a velocity of 28 meters per second.

'Tis long. A cannon-ball would reach the Sun in ten years. Light, that
rapid arrow that flies through space at a velocity of 300,000 kilometers
(186,000 miles per second), takes only eight minutes seventeen seconds
to traverse this distance.

* * * * *

This brilliant Sun is not only sovereign of the Earth; he is also the
head of a vast planetary system.

The orbs that circle round the Sun are opaque bodies, spherical in
shape, receiving their light and heat from the central star, on which
they absolutely depend. The name of planets given to them signifies
"wandering" stars. If you observe the Heavens on a fine starry night,
and are sufficiently acquainted with the principal stars of the Zodiac
as described in a preceding chapter, you may be surprised on certain
evenings to see the figure of some zodiacal constellation slightly
modified by the temporary presence of a brilliant orb perhaps surpassing
in its luminosity the finest stars of the first magnitude.

If you watch this apparition for some weeks, and examine its position
carefully in regard to the adjacent stars, you will observe that it
changes its position more or less slowly in the Heavens. These wandering
orbs, or _planets_, do not shine with intrinsic light; they are
illuminated by the Sun.

The planets, in effect, are bodies as opaque as the Earth, traveling
round the God of Day at a speed proportional to their distance. They
number eight principal orbs, and may be divided into two quite distinct
groups by which we may recognize them: the first comprises four planets,
of relatively small dimensions in comparison with those of the second
group, which are so voluminous that the least important of them is
larger than the other four put together.

In order of distance from the Sun, we fi