ntellect; but when it came to be recognised that this globe was but one
of a whole group of similar objects, some smaller, no doubt, but others
very much larger, and when it was further ascertained that these bodies
were subordinated to the supreme control of the sun, we have a chain of
discoveries that wrought a fundamental transformation in human
knowledge.

We thus see that the sun presides over a numerous family. The members of
that family are dependent upon the sun, and their dimensions are
suitably proportioned to their subordinate position. Even Jupiter, the
largest member of that family, does not contain one-thousandth part of
the material which forms the vast bulk of the sun. Yet the bulk of
Jupiter alone would exceed that of the rest of the planets were they all
rolled together.

Around the central luminary in Fig. 31 we have drawn four circles in
dotted lines which sufficiently illustrate the orbits in which the
different bodies move. The innermost of these four paths represents the
orbit of the planet Mercury. The planet moves around the sun in this
path, and regains the place from which it started in eighty-eight days.

The next orbit, proceeding outwards from the sun, is that of the planet
Venus, which we have already referred to as the well-known Evening Star.
Venus completes the circuit of its path in 225 days. One step further
from the sun and we come to the orbit of another planet. This body is
almost the same size as Venus, and is therefore much larger than
Mercury. The planet now under consideration accomplishes each revolution
in 365 days. This period sounds familiar to our ears. It is the length
of the year; and the planet is the earth on which we stand. There is an
impressive way in which to realise the length of the road along which
the earth has to travel in each annual journey. The circumference of a
circle is about three and one-seventh times the diameter of the same
figure; so that taking the distance from the earth to the centre of the
sun as 92,900,000 miles, the diameter of the circle which the earth
describes around the sun will be 185,800,000 miles, and consequently
the circumference of the mighty circle in which the earth moves round
the sun is fully 583,000,000 miles. The earth has to travel this
distance every year. It is merely a sum in division to find how far we
have to move each second in order to accomplish this long journey in a
twelvemonth. It will appear that the earth must