the shortness of the time during which we are able to observe them. It
is like viewing the plume of smoke issuing from a steamer, hull down,
at sea: if one does not continue to watch it for a long time it
appears to be motionless, although in reality it may be traveling at
great speed across the line of sight. Even the planets seem fixed in
position if one watches them for a single night only, and the more
distant ones do not sensibly change their places, except after many
nights of observation. Neptune, for instance, moves but little more
than two degrees in the course of an entire year, and in a month its
change of place is only about one-third of the diameter of the full
moon.

Yet, fixed as they seem, the stars are actually moving with a speed in
comparison with which, in some cases, the planets might almost be said
to stand fast in their tracks. Jupiter's speed in his orbit is about
eight miles per second, Neptune's is less than three and one-half
miles, and the earth's is about eighteen and one-half miles; while
there are ``fixed stars'' which move two hundred or three hundred
miles per second. They do not all, however, move with so great a
velocity, for some appear to travel no faster than the planets. But in
all cases, notwithstanding their real speed, long-continued and
exceedingly careful observations are required to demonstrate that they
are moving at all. No more overwhelming impression of the frightful
depths of space in which the stars are buried can be obtained than by
reflecting upon the fact that a star whose actual motion across the
line of sight amounts to two hundred miles per second does not change
its apparent place in the sky, in the course of a thousand years,
sufficiently to be noticed by the casual observer of the heavens!

There is one vast difference between the motions of the stars and