nsidering that
there is, we may fall into an error very much like that into which our
predecessors fell in thinking it entirely out of the range of
reasonable probability that the stars should be placed at such
distances as we now know them to be.

Accepting it as a fact that agencies do exist which travel from sun to
planet and from star to star with a speed which beggars all our
previous ideas, the first question that arises is that of their nature
and mode of action. This question is, up to the present time, one which
we do not see any way of completely answering. The first difficulty is
that we have no evidence of these agents except that afforded by their
action. We see that the sun goes through a regular course of
pulsations, each requiring eleven years for completion; and we see
that, simultaneously with these, the earth's magnetism goes through a
similar course of pulsations. The connection of the two, therefore,
seems absolutely proven. But when we ask by what agency it is possible
for the sun to affect the magnetism of the earth, and when we trace the
passage of some agent between the two bodies, we find nothing to
explain the action. To all appearance, the space between the earth and
the sun is a perfect void. That electricity cannot of itself pass
through a vacuum seems to be a well-established law of physics. It is
true that electromagnetic waves, which are supposed to be of the same
nature with those of light, and which are used in wireless telegraphy,
do pass through a vacuum and may pass from the sun to the earth. But
there is no way of explaining how such waves would either produce or
affect the magnetism of the earth.

The mysterious emanations from various substances, under certain
conditions, may have an intimate relation with yet another of the
mysteries of the universe. It is a fundamental law of the universe that
when a body emits light or heat, or anything capable of being
transformed into light or heat, it can do so only by the expenditure of
force, limited in supply. The sun and stars are continually sending out
a flood of heat. They are exhausting the internal supply of something
which must be limited in extent. Whence comes the supply? How is the
heat of the sun kept up? If it were a hot body cooling off, a very few
years would suffice for it to cool off so far that its surface would
become solid and very soon cold. In recent years, the theory
universally accepted has been that the supply o