ot exact enough to lead to any useful
results, and the existence of his 'planet stars' was at that time
derided, and believed to find a place only in his imagination.

The conclusions arrived at by some astronomers with regard to double
stars were afterwards confirmed by Herschel, when, by his observation of
a change in the relative positions of many of their components, he was
able to announce that they form independent systems in mutual
revolution, and are controlled by the law of gravitation.

The number of binary stars in active revolution is known to exceed 500;
but, besides these, there are doubtless numerous other compound stars
which, on account of their extreme remoteness and the close proximity of
their components, are irresolvable into pairs by any optical appliances
which we possess.

The revolution of two suns in one sphere presents to our observation a
scheme of creative design entirely different to the single-star system
with which we are familiar--one of a higher and more complex order in
the ascending scale of celestial architecture. For, if we assume that
around each revolving sun there circles a retinue of planetary worlds,
it is obvious that a much more complicated arrangement must exist among
the orbs which enter into the formation of such a system than is found
among those which gravitate round our Sun.

The common centre of gravity of a binary system is situated on a line
between both stars, and distant from each in inverse proportion to their
respective masses. When the stars are of equal mass their orbits are of
equal dimensions, but when the mass of one star exceeds that of the
other, the orbit of the larger star is proportionately diminished as
compared with the circumference traversed by the smaller star. When
their orbits are circular--a rare occurrence--both stars pursue each
other in the same path, and invariably occupy it at diametrically
opposite points; nor is it possible for one star to approach the other
by the minutest interval of space in any duration of time, so long as
the synchronous harmony of their revolution remains undisturbed.

[Illustration: FIG. 3.--A Binary Star System--70 Ophiuchi

(_Drawn by Mr. J. E. Gore._)]

When a pair of suns move in an ellipse, their orbits intersect and are
of equal dimensions when the stars are of equal mass, their common
centre of gravity being then at a point equidistant from each.
Consequently, neither star can approach or recede from