vens near
the constellation Lyra. The velocity with which the motion is performed
corresponds to the magnitude of the system; quicker than the swiftest
rifle-bullet that was ever fired, the sun, bearing with it the earth and
all the other planets, is now sweeping onwards. We on the earth
participate in that motion. Every half hour we are something like ten
thousand miles nearer to the constellation of Lyra than we should have
been if the solar system were not animated by this motion. As we are
proceeding at this stupendous rate towards Lyra, it might at first be
supposed that we ought soon to get there; but the distances of the stars
in that neighbourhood seem not less than those of the stars elsewhere,
and we may be certain that the sun and his system must travel at the
present rate for far more than a million years before we have crossed
the abyss between our present position and the frontiers of Lyra. It
must, however, be acknowledged that our estimate of the actual _speed_
with which our solar system is travelling is exceedingly uncertain, but
this does not in the least affect the fact that we are moving in the
direction first approximately indicated by Herschel (_see_ Chapter
XXIII.).

It remains to explain the method of reasoning which Herschel adopted, by
which he was able to make this great discovery. It may sound strange to
hear that the detection of the motion of the sun was not made by looking
at the sun; all the observations of the luminary itself with all the
telescopes in the world would never tell us of that motion, for the
simple reason that the earth, whence our observations must be made,
participates in it. A passenger in the cabin of a ship usually becomes
aware that the ship is moving by the roughness of the sea; but if the
sea be perfectly calm, then, though the tables and chairs in the cabin
are moving as rapidly as the ship, yet we do not see them moving,
because we are also travelling with the ship. If we could not go out of
the cabin, nor look through the windows, we would never know whether the
ship was moving or at rest; nor could we have any idea as to the
direction in which the ship was going, or as to the velocity with which
that motion was performed.

The sun, with his attendant host of planets and satellites, may be
likened to the ship. The planets may revolve around the sun just as the
passengers may move about in the cabin, but as the passengers, by
looking at objects on board, can ne