ppear as if they radiated outwards from
this point. In observations of these bodies the attention of astronomers
is directed to registering the path and speed of each meteor, and to
ascertaining the position of the radiant. It is from data such as these
that computations concerning the swarms and their orbits are made.

[Illustration: FIG. 20.--Passage of the Earth through the thickest
portion of a Meteor Swarm. The Earth and the Meteors are here
represented as approaching each other from opposite directions.]

For the present state of knowledge concerning meteors, astronomy is
largely indebted to the researches of Mr. W.F. Denning, of Bristol, and
of the late Professor A.S. Herschel.

During the course of each year the earth encounters a goodly number of
meteor-swarms. Three of these, giving rise to fine displays, are very
well known--the "Perseids," or August Meteors, and the "Leonids" and
"Bielids," which appear in November.

Of the above three the _Leonid_ display is by far the most important,
and the high degree of attention paid to it has laid the foundation of
meteoric astronomy in much the same way that the study of the
fascinating corona has given such an impetus to our knowledge of the
sun. The history of this shower of meteors may be traced back as far as
A.D. 902, which was known as the "Year of the Stars." It is related that
in that year, on the night of October 12th--the shower now comes about a
month later--whilst the Moorish King, Ibrahim Ben Ahmed, lay dying
before Cosenza, in Calabria, "a multitude of falling stars scattered
themselves across the sky like rain," and the beholders shuddered at
what they considered a dread celestial portent. We have, however, little
knowledge of the subsequent history of the Leonids until 1698, since
which time the maximum shower has appeared with considerable regularity
at intervals of about thirty-three years. But it was not until 1799 that
they sprang into especial notice. On the 11th November in that year a
splendid display was witnessed at Cumana, in South America, by the
celebrated travellers, Humboldt and Bonpland. Finer still, and
surpassing all displays of the kind ever seen, was that of November 12,
1833, when the meteors fell thick as snowflakes, 240,000 being estimated
to have appeared during seven hours. Some of them were even so bright as
to be seen in full daylight. The radiant from which the meteors seem to
diverge was ascertained to be situated in the