ver tell whither the ship is going,
so we, by merely looking at the sun, or at the other planets or members
of the solar system, can never tell if our system as a whole is in
motion.

The conditions of a perfectly uniform movement along a perfectly calm
sea are not often fulfilled on the waters with which we are acquainted,
but the course of the sun and his system is untroubled by any
disturbance, so that the majestic progress is conducted with absolute
uniformity. We do not feel the motion; and as all the planets are
travelling with us, we can get no information from them as to the common
motion by which the whole system is animated.

The passengers are, however, at once apprised of the ship's motion when
they go on deck, and when they look at the sea surrounding them. Let us
suppose that their voyage is nearly accomplished, that the distant land
appears in sight, and, as evening approaches, the harbour is discerned
into which the ship is to enter. Let us suppose that the harbour has, as
is often the case, a narrow entrance, and that its mouth is indicated by
a lighthouse on each side. When the harbour is still a long way off,
near the horizon, the two lights are seen close together, and now that
the evening has closed in, and the night has become quite dark, these
two lights are all that remain visible. While the ship is still some
miles from its destination the two lights seem close together, but as
the distance decreases the two lights seem to open out; gradually the
ship gets nearer, while the lights are still opening, till finally, when
the ship enters the harbour, instead of the two lights being directly in
front, as at the commencement, one of the lights is passed by on the
right hand, while the other is similarly found on the left. If, then, we
are to discover the motion of the solar system, we must, like the
passenger, look at objects unconnected with our system, and learn our
own motion by their apparent movements. But are there any objects in the
heavens unconnected with our system? If all the stars were like the
earth, merely the appendages of our sun, then we never could discover
whether we were at rest or whether we were in motion: our system might
be in a condition of absolute rest, or it might be hurrying on with an
inconceivably great velocity, for anything we could tell to the
contrary. But the stars do not belong to the system of our sun; they
are, rather, suns themselves, and do not recognise the s