gradually,
however, the faster runners get ahead and the slower ones lag behind, so
the cluster becomes elongated. As the race continues, the cluster
becomes dispersed around the entire course, and perhaps the first boy
will even overtake the last. Such seems the destiny of the November
meteors in future ages. The cluster will in time come to be spread out
around the whole of this mighty track, and no longer will a superb
display have to be recorded every thirty-three years.

It was in connection with the shower of November meteors in 1866 that a
very interesting and beautiful discovery in mathematical astronomy was
made by Professor Adams. We have seen that the Leonids must move in an
elliptic path, and that they return every thirty-three years, but the
telescope cannot follow them during their wanderings. All that we know
by observation is the date of their occurrence, the point of the heavens
from which they radiate, and the great return every thirty-three years.
Putting these various facts together, it is possible to determine the
ellipse in which the meteors move--not exactly: the facts do not go so
far--they only tell us that the ellipse must be one of five possible
orbits. These five possible orbits are--firstly, the immense ellipse in
which we now know the meteorites do revolve, and for which they require
the whole thirty-three years to complete a revolution; secondly, a
nearly circular orbit, very little larger than the earth's path, which
the meteors would traverse in a few days more than a year; another
similar orbit, in which the time would be a few days short of the year;
and two other small elliptical orbits lying inside the earth's orbit. It
was clearly demonstrated by Professor Newton, of New Haven, U.S.A., that
the observed facts would be explained if the meteors moved in any one of
these paths, but that they could not be explained by any other
hypothesis. It remained to see which of these orbits was the true one.
Professor Newton himself made the suggestion of a possible method of
solving the problem. The test he proposed was one of some difficulty,
for it involved certain intricate calculations in the theory of
perturbations. Fortunately, however, Professor Adams undertook the
inquiry, and by his successful labours the path of the Leonids has been
completely ascertained.

[Illustration: Fig. 78.--The History of the Leonids.]

When the ancient records of the appearance of great Leonid showers were