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 of heat is kept up by the continual
contraction of the sun, by mutual gravitation of its parts as it
cools off. This theory has the advantage of enabling us to
calculate, with some approximation to exactness, at what rate the
sun must be contracting in order to keep up the supply of heat
which it radiates.
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