, of course, quite invisible to the unaided eye), which
later on was seen to have moved, and was thus shown to be vastly nearer
the earth than any true star. He at first supposed, as Herschel had
done when he first saw Uranus, that the unfamiliar body was a comet; but
later observation proved it a tiny planet, occupying a position in space
between Mars and Jupiter. It was christened Ceres, after the tutelary
goddess of Sicily.

Though unpremeditated, this discovery was not unexpected, for
astronomers had long surmised the existence of a planet in the wide
gap between Mars and Jupiter. Indeed, they were even preparing to make
concerted search for it, despite the protests of philosophers, who
argued that the planets could not possibly exceed the magic number
seven, when Piazzi forestalled their efforts. But a surprise came
with the sequel; for the very next year Dr. Olbers, the wonderful
physician-astronomer of Bremen, while following up the course of Ceres,
happened on another tiny moving star, similarly located, which soon
revealed itself as planetary. Thus two planets were found where only one
was expected.

The existence of the supernumerary was a puzzle, but Olbers solved it
for the moment by suggesting that Ceres and Pallas, as he called his
captive, might be fragments of a quondam planet, shattered by internal
explosion or by the impact of a comet. Other similar fragments, he
ventured to predict, would be found when searched for. William Herschel
sanctioned this theory, and suggested the name asteroids for the tiny
planets. The explosion theory was supported by the discovery of another
asteroid, by Harding, of Lilienthal, in 1804, and it seemed clinched
when Olbers himself found a fourth in 1807. The new-comers were named
Juno and Vesta respectively.

There the case rested till 1845, when a Prussian amateur astronomer
named Hencke found another asteroid, after long searching, and opened a
new epoch of discovery. From then on the finding of asteroids became a
commonplace. Latterly, with the aid of photography, the list has been
extended to above four hundred, and as yet there seems no dearth in the
supply, though doubtless all the larger members have been revealed. Even
these are but a few hundreds of miles in diameter, while the smaller
ones are too tiny for measurement. The combined bulk of these minor
planets is believed to be but a fraction of that of the earth.

Olbers's explosion theory, long accepted by a