mplete his work,
formed nine new constellations in those spaces in the celestial vault
which were previously un-named. They are known by the names
Camelopardus, Canes Venatici, Coma Bernices, Lacerta, Leo Minor, Lynx,
Monoceros, Sextans, and Vulpecula. He also executed a chart of the
Moon's surface, wrote a description of the lunar spots, and discovered
the Libration of the Moon in Longitude.

On May 30, 1661, Hevelius observed a transit of Mercury, a description
of which he published, and included with it Horrox's treatise on the
first-recorded transit of Venus. This work, after having passed through
several hands, became the property of Hevelius, who was capable of
appreciating its merits. The manuscript was sent to him by Huygens, and
in acknowledging it he writes: 'How greatly does my Mercury exult in the
joyous prospect that he may shortly fold within his arms Horrox's long
looked-for and beloved Venus! He renders you unfeigned thanks that by
your permission this much-desired union is about to be celebrated, and
that the writer is able, with your concurrence, to introduce them both
together to the public.'

Hevelius made numerous researches on comets, and suggested that the
form of their paths might be a parabola.

GIOVANNI DOMENICO CASSINI was born at Perinaldo, near Nice, in 1625. He
studied at Genoa and Bologna, and was afterwards appointed to the Chair
of Astronomy at the latter University. He was a man of high scientific
attainments, and made many important astronomical discoveries.

In 1671 he became Director of the Royal Observatory at Paris, and
devoted a long life to trying and difficult observations, which in his
later years deprived him of his eyesight.

In 1644 Cassini proved beyond doubt that Jupiter rotated on his axis,
and also assigned his period of rotation with considerable accuracy. He
published tables of the planet's satellites, and determined their
motions from observations of their eclipses. He ascertained the periods
of rotation of Venus and Mars; executed a chart of the lunar surface,
and observed an occultation of Jupiter by the Moon.

Cassini discovered the dual nature of Saturn's ring, having perceived
that instead of one there are two concentric rings separated by a dark
space. He also discovered four of the planet's satellites--viz. Japetus,
Rhea, Dione, and Tethys. He made a near approximation to the solar
parallax by means of researches on the parallax of Mars, and
investigated