h resistance, by
diminishing its actual velocity, would diminish its centrifugal force.
Accordingly, this is the solution proposed by Encke, and at present
generally received."

So that we have in Encke's Comet another proof of the existence of that
aetherial medium, which is not frictionless, but has the power to oppose
any body which moves through it, when that body moves in an opposite
direction to its own motions.

Another Short Period Comet worthy of notice is that of Biela, named
after M. Biela, its discoverer. This comet had a period of six and a half
years, and reappeared at several successive intervals until about the
year 1845, when it seems to have been broken or split up into two parts.
In December 1845 the comet divided into two parts, which travelled
parallel to each other for a long distance. During this separation, very
singular changes were observed to be taking place in both the original
comet and its offshoot.

Both had a nucleus, and both had tails, which were parallel to each
other. The comets continued to travel together until the 15th March
1846, when the new comet began to fade away, until, on the 24th March,
the old comet only was visible, while in April both had disappeared
entirely. A similar phenomenon was again observed at its next passage in
1852, but since then Biela's Comet has entirely disappeared. It is
suggested by astronomers, that the comet has become condensed, and
broken up, forming a shoal of meteors.

Support is lent to this theory by the fact that in November 1872, when
the earth was passing through space and had arrived at that part of its
orbit which intercepted the orbit of Biela's Comet, instead of the comet
being seen, the earth came into contact with a swarm of meteors, and
this is accepted as evidence that Biela's Comet was condensed far away
in the colder regions of interplanetary space into a more solid form of
matter, known as meteors. One of the more famous of the short period
class of comets is that known as Halley's Comet, which has a period of
about 76 years. This comet has been seen in its return journey to the
sun about 25 times. It was named after its discoverer, Edmund Halley. He
was led to identify this comet with that of 1531 and 1607, and thus to
conclude that it had a period of 75 or 76 years. He therefore predicted
its reappearance in 1759. As the year approached, its arrival was
eagerly looked for, to see if the prediction would be verified.

It was