objects extends at right angles to the road, and from
the road to the horizon. Now, as we proceed along the road, we see these
objects changing their positions, respectively, in relation to a certain
fixed point in that portion of the firmament which forms the background
of the view. Let us suppose this fixed point--sufficiently fixed for our
purpose--to be the rising moon. We become aware, at once, that while the
tree nearest us so far alters its position in respect to the moon, as to
seem flying behind us, the tree in the extreme distance has scarcely
changed at all its relative position with the satellite. We then go on
to perceive that the farther the objects are from us, the less they
alter their positions; and the converse. Then we begin, unwittingly, to
estimate the distances of individual trees by the degrees in which they
evince the relative alteration. Finally, we come to understand how it
might be possible to ascertain the actual distance of any given tree in
the line, by using the amount of relative alteration as a basis in a
simple geometrical problem. Now this relative alteration is what we call
"parallax;" and by parallax we calculate the distances of the heavenly
bodies. Applying the principle to the trees in question, we should, of
course, be very much at a loss to comprehend the distance of _that_
tree, which, however far we proceeded along the road, should evince _no_
parallax at all. This, in the case described, is a thing impossible; but
impossible only because all distances on our Earth are trivial
indeed:--in comparison with the vast cosmical quantities, we may speak of
them as absolutely nothing.

Now, let us suppose the star Alpha Lyrae directly overhead; and let us
imagine that, instead of standing on the Earth, we stand at one end of a
straight road stretching through Space to a distance equalling the
diameter of the Earth's orbit--that is to say, to a distance of 190
_millions of miles_. Having observed, by means of the most delicate
micrometrical instruments, the exact position of the star, let us now
pass along this inconceivable road, until we reach its other extremity.
Now, once again, let us look at the star. It is _precisely_ where we
left it. Our instruments, however delicate, assure us that its relative
position is absolutely--is identically the same as at the commencement of
our unutterable journey. _No_ parallax--none whatever--has been found.

The fact is, that, in regard to the di