that the meteor cluster was at perihelion. The period being known, the
eccentricity of the orbit was obtainable, also the orbital velocity of
the meteors in perihelion; and, by comparing this with the earth's
velocity, the latitude of the radiant enabled the inclination to be
determined, while the longitude of the earth that night was the
longitude of the node. In such a way Schiaparelli was able to find
first the elements of the orbit of the August meteor shower
(Perseids), and to show its identity with the orbit of Tuttle's comet
1862.iii. Then, in January 1867, Le Verrier gave the elements of the
November meteor shower (Leonids); and Peters, of Altona, identified
these with Oppolzer's elements for Tempel's comet 1866--Schiaparelli
having independently attained both of these results. Subsequently
Weiss, of Vienna, identified the meteor shower of April 20th (Lyrids)
with comet 1861. Finally, that indefatigable worker on meteors,
A. S. Herschel, added to the number, and in 1878 gave a list of
seventy-six coincidences between cometary and meteoric orbits.

Cometary astronomy is now largely indebted to photography, not merely
for accurate delineations of shape, but actually for the discovery of
most of them. The art has also been applied to the observation of
comets at distances from their perihelia so great as to prevent their
visual observation. Thus has Wolf, of Heidelburg, found upon old
plates the position of comet 1905.v., as a star of the 15.5 magnitude,
783 days before the date of its discovery. From the point of view of
the importance of finding out the divergence of a cometary orbit from
a parabola, its period, and its aphelion distance, this increase of
range attains the very highest value.

The present Astronomer Royal, appreciating this possibility, has been
searching by photography for Halley's comet since November, 1907,