e of the most remarkable features of tails is their abnormal length,
which oftentimes reaches into millions of miles. The comet of 1843 had a
tail 112,000,000 miles long. Another feature about the tails of comets
is that they are always directed _away_ from the sun. Up to the present
I believe no satisfactory explanation has been given of this fact, but
with the conception of the rotating Aether as given in Art. 94, we shall
for the first time be able to give a satisfactory physical explanation
of that phenomenon. In addition to this, the formation of cometary tails
of all shapes receives a physical explanation, when taken into account
with the fact that the sun is an electro-magnet, possessing its
electro-magnetic field, and its lines of force, as described in Art. 88.

[Footnote 41: _Outlines of Astronomy._]

[Footnote 42: _Outlines of Astronomy._]

ART. 115. _Centrifugal Force and Comets' Tails._--In order to account
for the existence of the tails of comets, various repulsive forces have
been introduced from time to time into the solar system, so that the
phenomena of cometary tails might be satisfactorily accounted for.

It has been felt by every astronomer that some repulsive force, which
had its origin in the sun, was absolutely necessary to explain the
existence of the tails, and as no real force could be demonstrated to
exist, recourse had to be made to repulsive forces of a more or less
hypothetical nature. The necessity of this repulsive force is nowhere
more plainly indicated than by Sir J. Herschel in his _Lectures on
Scientific Subjects_, where, dealing with the phenomena of comets'
tails, he writes: "They have furnished us with a proof, amounting to
demonstration, of the existence of a repulsive force directed from the
sun, as well as that great and general attractive force which keeps
planets in their orbits."

In the same work, referring to the comet of 1680, he writes: "This comet
was perhaps the most magnificent ever seen. It appeared from November
1680 to March 1681. In its approach to the sun it was not very bright,
but began to throw out its tail when about as far from the sun as the
earth. It passed its perihelion on December 8th, and when nearest to the
sun was only about 1/10 part of the sun's diameter from the surface. No
wonder it gave evidence of violent excitement, coming from the cold
region outside planetary space. Already, when arrived even in our
temperate regions, it began to show