e distant horizon, we can hardly notice that the steamer is
moving. It is true that by looking again in a few minutes we can detect
a change in its place; but the motion of the steamer seems slow. Yet if
we were near the steamer we would find that it was rushing along at the
rate of many miles an hour. It is the distance which causes the
illusion. So it is with the stars: they seem to move slowly because they
are very distant, but were we near them, we could see that in the
majority of cases their motions are a thousand times as fast as the
quickest steamer that ever ploughed the ocean.

It thus appears that the permanence of the sidereal heavens, and the
fixity of the constellations in their relative positions, are only
ephemeral. When we rise to the contemplation of such vast periods of
time as the researches of geology disclose, the durability of the
constellations vanishes! In the lapse of those stupendous ages stars and
constellations gradually dissolve from view, to be replaced by others of
no greater permanence.

It not unfrequently happens that a parallax research proves abortive.
The labour has been finished, the observations are reduced and
discussed, and yet no value of the parallax can be obtained. The
distance of the star is so vast that our base-line, although it is
nearly two hundred millions of miles long, is too short to bear any
appreciable ratio to the distance of the star. Even from such failures,
however, information may often be drawn.

Let me illustrate this by an account derived from my own experience at
Dunsink. We have already mentioned that on the 24th November, 1876, a
well-known astronomer--Dr. Schmidt, of Athens--noticed a new bright star
of the third magnitude in the constellation Cygnus. On the 20th of
November Nova Cygni was invisible. Whether it first burst forth on the
21st, 22nd, or 23rd no one can tell; but on the 24th it was discovered.
Its brilliancy even then seemed to be waning; so, presumably, it was
brightest at some moment between the 20th and 24th of November. The
outbreak must thus have been comparatively sudden, and we know of no
cause which would account for such a phenomenon more simply than a
gigantic collision. The decline in the brilliancy was much more tardy
than its growth, and more than a fortnight passed before the star
relapsed into insignificance--two or three days (or less) for the rise,
two or three weeks for the fall. Yet even two or three weeks was a short