the contrast of colours better than when the telescope
exhibits merely two stellar points.

Such are a few of these double and multiple stars. Their numbers are
being annually augmented; indeed, one observer--Mr. Burnham, formerly on
the staff of the Lick Observatory, and now an observer in the Yerkes
Observatory--has added by his own researches more than 1,000 new doubles
to the list of those previously known.

The interest in this class of objects must necessarily be increased when
we reflect that, small as the stars appear to be in our telescopes, they
are in reality suns of great size and splendour, in many cases rivalling
our own sun, or, perhaps, even surpassing him. Whether these suns have
planets attending upon them we cannot tell; the light reflected from the
planet would be utterly inadequate to the penetration of the vast extent
of space which separates us from the stars. If there be planets
surrounding these objects, then, instead of a single sun, such planets
will be illuminated by two, or, perhaps, even more suns. What wondrous
effects of light and shade must be the result! Sometimes both suns will
be above the horizon together, sometimes only one sun, and sometimes
both will be absent. Especially remarkable would be the condition of a
planet whose suns were of the coloured type. To-day we have a red sun
illuminating the heavens, to-morrow it would be a blue sun, and,
perhaps, the day after both the red sun and the blue sun will be in the
firmament together. What endless variety of scenery such a thought
suggests! There are, however, grave dynamical reasons for doubting
whether the conditions under which such a planet would exist could be
made compatible with life in any degree resembling the life with which
we are familiar. The problem of the movement of a planet under the
influence of two suns is one of the most difficult that has ever been
proposed to mathematicians, and it is, indeed, impossible in the present
state of analysis to solve with accuracy all the questions which it
implies. It seems not at all unlikely that the disturbances of the
planet's orbit would be so great that it would be exposed to
vicissitudes of light and of temperature far transcending those
experienced by a planet moving, like the earth, under the supreme
control of a single sun.

CHAPTER XXI.

THE DISTANCES OF THE STARS.

Sounding-line for Space--The Labours of Bessel--Meaning of Annual
Parallax--Minute