uld soar up and up never to return. In a future
chapter it will be necessary to refer again to this subject.

A few of the minor planets appear in powerful telescopes as discs with
appreciable dimensions, and they have even been measured with the
micrometer. In this way Professor Barnard, late of the Lick Observatory,
determined the following values for the diameters of the four first
discovered minor planets:--

Ceres 485 miles.
Pallas 304 miles.
Juno 118 miles.
Vesta 243 miles.

The value for Juno is, however, very uncertain, and by far the greater
number of the minor planets are very much smaller than the figures here
given would indicate. It is possible by a certain calculation to form an
estimate of the aggregate mass of all the minor planets, inasmuch as
observations disclose to us the extent of their united disturbing
influences on the motion of Mars. In this manner Le Verrier concluded
that the collected mass of the small planets must be about equal to
one-fourth of the mass of the earth. Harzer, repeating the enquiry in an
improved manner, deduced a collected mass one-sixth of that of the
earth. There can be no doubt that the total mass of all the minor
planets at present known is not more than a very small fraction of the
amount to which these calculations point. We therefore conclude that
there must be a vast number of minor planets which have not yet been
recognised in the observatory. These unknown planets must be extremely
minute.

The orbits of this group of bodies differ in remarkable characteristics
from those of the larger planets. Some of them are inclined at angles of
30 deg. to the plane of the earth's orbit, the inclinations of the great
planets being not more than a few degrees. Some of the orbits of the
minor planets are also greatly elongated ellipses, while, of course, the
orbits of the large planets do not much depart from the circular form.
The periods of revolution of these small objects round the sun range
from three years to nearly nine years.

A great increase in the number of minor planets has rewarded the zeal of
those astronomers who have devoted their labours to this subject. Their
success has entailed a vast amount of labour on the computers of the
"Berlin Year-Book." That useful work occupies in this respect a position
which has not been taken by our own "Nautical Almanac," nor by the
similar publications of other countries. A skilful band of c