correct answer. Not only from every position of the
earth, but from every planet of the solar system, the same
constellations are visible, and the stars have the same aspect. The
whole immensity of the solar system shrinks to practically a point
when confronted with the distance of the stars.

Not, however, so entirely a speck as to resist the terrific
accuracy of the present century, and their microscopic relative
displacement with the season of the year has now at length been
detected, and the distance of many thereby measured.

3. That, if the earth revolved round the sun, Mercury and Venus ought to
show phases like the moon.

So they ought. Any globe must show phases if it live nearer the sun
than we do and if we go round it, for we shall see varying amounts
of its illuminated half. The only answer that Copernicus could give
to this was that they might be difficult to see without extra
powers of sight, but he ventured to predict that the phases would
be seen if ever our powers of vision should be enhanced.

4. That if the earth moved, or even revolved on its own axis, a stone or
other dropped body ought to be left far behind.

This difficulty is not a real one, like the two last, and it is
based on an ignorance of the laws of mechanics, which had not at
that time been formulated. We know now that a ball dropped from a
high tower, so far from lagging, drops a minute trifle _in front_
of the foot of a perpendicular, because the top of the tower is
moving a trace faster than the bottom, by reason of the diurnal
rotation. But, ignoring this, a stone dropped from the lamp of a
railway carriage drops in the centre of the floor, whether the
carriage be moving steadily or standing still; a slant direction of
fall could only be detected if the carriage were being accelerated
or if the brake were applied. A body dropped from a moving carriage
shares the motion of the carriage, and starts with that as its
initial velocity. A ball dropped from a moving balloon does not
simply drop, but starts off in whatever direction the car was
moving, its motion being immediately modified by gravity, precisely
in the same way as that of a thrown ball is modified. This is,
indeed, the whole philosophy of throwing--to drop a ball from a
moving carriage. The carriage is the hand, an