The
distance and size of the sun or of any of the planets can be
proved; the length of their days and years, and even the weight of
the matter of which they are composed. Such things will probably
appear to you impossible, if you have read nothing of them;
especially when you hear that the sun is ninety-five millions of
miles off, and that the planet Neptune, which is the farthest known
planet from the sun, is at such a distance that the light of the
sun takes about five hours to reach it; that is, the sun is
actually five hours above the horizon before the people there see
it rise. Its distance is 2850 millions of miles, and the sun as
seen by them is not larger than Venus appears to us when an evening
star. And although this planet is so distant that it can only be
seen with large telescopes, they can not only compute its distance
and size, but also the mass of matter of which it is composed. But
you will find all this thrown into the shade by the way in which it
was discovered. As I may be telling you what you know already, I
will merely state, that from observed perturbations in the course
of the planet Uranus, it was supposed that another planet was in
existence beyond it; and two competitors set to work to calculate
its size, situation, etc.
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