er village or building, we know,
lies such and such a number of miles away.

The measurements which have already been given of the diameters of the
various bodies of the solar system appear very great to us, who find
that a walk of a few miles at a time taxes our strength; but they are a
mere nothing when we consider the distances from the sun at which the
various planets revolve in their orbits.

The following table gives these distances in round numbers. As here
stated they are what are called "mean" distances; for, as the orbits are
oval, the planets vary in their distances from the sun, and we are
therefore obliged to strike a kind of average for each case:--

Mercury about 36,000,000 miles.
Venus " 67,200,000 "
Earth " 92,900,000 "
Mars " 141,500,000 "
Jupiter " 483,300,000 "
Saturn " 886,000,000 "
Uranus " 1,781,900,000 "
Neptune " 2,791,600,000 "

From the above it will be seen at a glance that we have entered upon a
still greater scale of distance than in dealing with the diameters of
the various bodies of the system. In that case the distances were
limited to thousands of miles; in this, however, we have to deal with
millions. A million being ten hundred thousand, it will be noticed that
even the diameter of the huge sun is well under a million miles.

How indeed are we to get a grasp of such distances, when those to which
we are ordinarily accustomed--the few miles' walk, the little stretch of
sea or land which we gaze upon around us--are so utterly minute in
comparison? The fact is, that though men may think that they can picture
in their minds such immense distances, they actually can not. In matters
like these we unconsciously employ a kind of convention, and we estimate
a thing as being two or three or more times the size of another. More
than this we are unable to do. For instance, our ordinary experience of
a mile enables us to judge, in a way, of a stretch of several miles,
such as one can take in with a glance; but in our estimation of a
thousand miles, or even of one hundred, we are driven back upon a mental
trick, so to speak.

In our attempts to realise such immense distances as those in the solar
system we are obliged to have recourse to analogies; to comparisons with
other and simpler facts, though this is at the best a mere self-cheating
device. The analogy which seems most suited to our purpose here, and one
which has often bee