ued and complete
measures of parallax yet made are those carried on by Gill, at the Cape
of Good Hope, on these two and some other bright stars. The results,
published in 1901, show that neither of these bodies has any parallax
that can be measured by the most refined instrumental means known to
astronomy. In other words, the distance of these stars is immeasurably
great. The actual amount of light emitted by each is certainly
thousands and probably tens of thousands of times that of the sun.

Notwithstanding the difficulties that surround the subject, we can at
least say something of the distance of a considerable number of the
stars. Two methods are available for our estimate--measures of parallax
and determination of proper motions.

The problem of stellar parallax, simple though it is in its conception,
is the most delicate and difficult of all which the practical
astronomer has to encounter. An idea of it may be gained by supposing a
minute object on a mountain-top, we know not how many miles away, to be
visible through a telescope. The observer is allowed to change the
position of his instrument by two inches, but no more. He is required
to determine the change in the direction of the object produced by this
minute displacement with accuracy enough to determine the distance of
the mountain. This is quite analogous to the determination of the
change in the direction in which we see a star as the earth, moving
through its vast circuit, passes from one extremity of its orbit to the
other. Representing this motion on such a scale that the distance of
our planet from the sun shall be one inch, we find that the nearest
star, on the same scale, will be more than four miles away, and
scarcely one out of a million will be at a less distance than ten
miles. It is only by the most wonderful perfection both in the
heliometer, the instrument principally used for these measures, and in
methods of observation, that any displacement at all can be seen even
among the nearest stars. The parallaxes of perhaps a hundred stars have
been determined, with greater or less precision, and a few hundred more
may be near enough for measurement. All the others are immeasurably
distant; and it is only by statistical methods based on their proper
motions and their probable near approach to equality in distribution
that any idea can be gained of their distances.

To form a conception of the stellar system, we must have a unit of
measure not o