that matter, as the later years of the eighteenth century
itself. Several of the prominent astronomers of
the later seventeenth century lived on into the opening
years of the following century, however, and the
younger generation soon developed a coterie of
astronomers, among whom Euler, Lagrange, Laplace,
and Herschel, as we shall see, were to accomplish great
things in this field before the century closed.

One of the great seventeenth-century astronomers,
who died just before the close of the century, was
Johannes Hevelius (1611-1687), of Dantzig, who advanced
astronomy by his accurate description of the
face and the spots of the moon. But he is remembered
also for having retarded progress by his influence
in refusing to use telescopic sights in his observations,
preferring until his death the plain sights long
before discarded by most other astronomers. The
advantages of these telescope sights have been discussed
under the article treating of Robert Hooke, but
no such advantages were ever recognized by Hevelius.
So great was Hevelius's reputation as an astronomer
that his refusal to recognize the advantage of the telescope
sights caused many astronomers to hesitate before
accepting them as superior to the plain; and even
the famous Halley, of whom we shall speak further in
a moment, was sufficiently in doubt over the matter
to pay the aged astronomer a visit to test his skill in
using the old-style sights. Side by side, Hevelius and
Halley made their observations, Hevelius with his old