lose. The stars, no doubt, would not exhibit the slightest change in
brilliancy. Each star shines by its own light and is not indebted to the
sun. The constellations would thus twinkle on as before, but a
wonderful change would come over the planets. Were the sun to be
obscured, the planets would also disappear from view. The midnight sky
would thus experience the effacement of the planets one by one, while
the stars would remain unaltered. It may seem difficult to realise how
the brilliancy of Venus or the lustre of Jupiter have their origin
solely in the beams which fall upon these bodies from the distant sun.
The evidence is, however, conclusive on the question; and it will be
placed before the reader more fully when we come to discuss the several
planets in detail.

Suppose that we are looking at Jupiter high in mid-heavens on a winter's
night, it might be contended that, as the earth lies between Jupiter and
the sun, it must be impossible for the rays of the sun to fall upon the
planet. This is, perhaps, not an unnatural view for an inhabitant of
this earth to adopt until he has become acquainted with the relative
sizes of the various bodies concerned, and with the distances by which
those bodies are separated. But the question would appear in a widely
different form to an inhabitant of the planet Jupiter. If such a being
were asked whether he suffered much inconvenience by the intrusion of
the earth between himself and the sun, his answer would be something of
this kind:--"No doubt such an event as the passage of the earth between
me and the sun is possible, and has occurred on rare occasions separated
by long intervals; but so far from the transit being the cause of any
inconvenience, the whole earth, of which you think so much, is really so
minute, that when it did come in front of the sun it was merely seen as
a small telescopic point, and the amount of sunlight which it
intercepted was quite inappreciable."

The fact that the planets shine by the sun's light points at once to the
similarity between them and our earth. We are thus led to regard our sun
as a central fervid globe associated with a number of much smaller
bodies, each of which, being dark itself, is indebted to the sun both
for light and for heat.

That was, indeed, a grand step in astronomy which demonstrated the
nature of the solar system. The discovery that our earth must be a
globe isolated in space was in itself a mighty exertion of human
i