of density | The Law of Gravitation
of the resisting medium which | (Art. 45).
surrounds the sun? |
|
2. Is it at rest or in motion? | In motion.
|
3. If the latter, in what | Rotates round the sun.
direction does it move? |
|
4. Circularly round the sun | Both, as it circulates round
or traversing space? | the sun while that body
| traverses space.
|
5. If circularly, in what | The plane of the ecliptic.
plane? |

ART. 95. _Physical Explanation of the Vibration in the Electro-Magnetic
Theory of Light._--In Art. 78 we learned that light was an
electro-magnetic disturbance in the Aether which was propagated through
the Aether, with a finite velocity; and from this we gathered that light
waves were nothing more or less than electro-magnetic waves, which were
radiated from the sun, out into the Aether on every side.

We were unable, however, at that time to give a definite physical
conception of the aetherial vibrations, or of the relation of the
various types of vibration to each other. Since, however, the
development of the Aether from the electric and magnetic standpoint,
which has led us up to the fact that the Aether possesses a circulating
motion round the sun (Art. 91), the solution of the problem appears
probable. I am of the opinion that the physical conception of the
various vibrations to each other is now within the region of
possibility, and in this article I wish to endeavour to give what seems
to me to be a correct and philosophical explanation of this part of the
electro-magnetic theory of light, the physical conception of which up to
the present has not been generally understood.

The explanation may, or may not, be fully complete, but even if it be
not perfectly correct, I am convinced that it will ultimately lead to a
satisfactory physical explanation of this part of Maxwell's Theory of
Light. In forming a conception as to the physical character of the
vibrations in the electro-magnetic theory, we have to remember that
there are three distinct vibrations, or motions, concerned in this
theory.

[Illustration: Fig: 22.]

1st. There is the direction of propagation.

2nd. There is the direction of the el