you reach the nearest star, and then another
twenty years before you reach another. At these awful distances from one
another the stars are scattered in space, and were they not brilliantly
self-luminous and glowing like our sun, they would be hopelessly
invisible.

I have spoken of 61 Cygni as a flying star, but there is another which
goes still quicker, a faint star, 1830 in Groombridge's Catalogue. Its
distance is far greater than that of 61 Cygni, and yet it is seen to
move almost as quickly. Its actual speed is about 200 miles a
second--greater than the whole visible firmament of fifty million stars
can control; and unless the universe is immensely larger than anything
we can see with the most powerful telescopes, or unless there are crowds
of invisible non-luminous stars mixed up with the others, it can only be
a temporary visitor to this frame of things; it is rushing from an
infinite distance to an infinite distance; it is passing through our
visible universe for the first and only time--it will never return. But
so gigantic is the extent of visible space, that even with its amazing
speed of 200 miles every second, this star will take two or three
million years to get out of sight of our present telescopes, and several
thousand years before it gets perceptibly fainter than it is now.

Have we any reason for supposing that the stars we see are all there
are? In other words, have we any reason for supposing all celestial
objects to be sufficiently luminous to be visible? We have every ground
for believing the contrary. Every body in the solar system is dull and
dark except the sun, though probably Jupiter is still red-hot. Why may
not some of the stars be dark too? The genius of Bessel surmised this,
and consistently upheld the doctrine that the astronomy of the future
would have to concern itself with dark and invisible bodies; he preached
"an astronomy of the invisible." Moreover he predicted the presence of
two such dark bodies--one a companion of Sirius, the other of Procyon.
He noticed certain irregularities in the motions of these stars which he
asserted must be caused by their revolving round other bodies in a
period of half a century. He announced in 1844 that both Sirius and
Procyon were double stars, but that their companions, though large, were
dark, and therefore invisible.

No one accepted this view, till Peters, in America, found in 1851 that
the hypothesis accurately explained the anomalous motion