We may well suppose such a power
extending its influence through and beyond the earth-crust, reaching out
towards the moon, and retro-acting with that body in preserving their
mutual relations.

Does not this mighty influence reach out toward the sun also, and act
conjointly with that great central orb in producing results, which to
us, have ever been great mysteries.[4]

_The Grand Magnetic Circuit._

In the retro-acting influence in operation between these great bodies,
may be found _A Grand Magnetic Circuit_. In this grand magnetic circuit
is found the _key_ to the whole subject of the correlation and identity
of all the forces.

And now, as preparatory to using this _key_ that we may enter in and
consider the intimate nature of the physical forces, we would be
impressed with the clear and full idea of this mighty _current_, which
bears upon its tide, _as one_, all manner of forces with which we have
to do.

It remains for us to tell what this great current _is_, and what it
_does_. To the child, to the savage, and to the civilized man alike, it
comes first and pre-eminently as light.

FOOTNOTES:

[2] Appendix, p. 98.

[3] Appendix, p. 99.

[4] Appendix, p. 99.

[A] The earth's core constitutes nearly 98/100 of its entire mass.

CHAPTER IV.

SUNLIGHT.

_Its Source and Nature._

Sunlight is one of the products of that grand retro-action which is
incessantly in operation between sun and earth, and is, in its intimate
and essential nature, a vito-magnetic _fluid_[B] (or so-called
magnetic). Subtle, and apparently intangible, manifesting itself rather
as a presence than a real substance, it fills all the space between the
sun and earth--which space may, with sufficient accuracy, be termed the
solar cone or cone-space.

_Its Limits._

Beyond the boundaries of the solar cone, _no light is_.

[Illustration: Pl. I. SOLAR CONE.]

_The Sun not Incandescent._

The apparent brightness of the sun is owing to the aggregation of the
93,000,000 of miles of this fluid which is present between the sun and
earth, or to our presence in the great current of activity of the
vito-magnetic force. It is therefore not due to a condition of
incandescence _at_ or _near_ that body. It is cool and habitable, and
emits no light. The brightness of the interv