nd a
Synopsis of the Scientific Writings of Sir WILLIAM HERSCHEL_," prepared
by Dr. HASTINGS and myself, and published by the Smithsonian
Institution.

An accurate sketch of the state of astronomy in England and on the
Continent, in the years 1780-1820, need not be given. It will be enough
if we remember that of the chief observatories of Europe, public and
private, no one was actively devoted to such labors as were undertaken
by HERSCHEL at the very beginning of his career.

His observations on variable stars, indeed, were in the same line as
those of PIGOTT; FLAUGERGUES and DARQUIER, in France, had perhaps
preceded him in minute scrutiny of the sun's surface, etc.; but, even in
that department of observation, he at once put an immense distance
between himself and others by the rapid and extraordinary advances in
the size and in the excellence of his telescopes. Before his time the
principal aids to observation were the Gregorian and Newtonian
telescopes of SHORT, and the small achromatics of DOLLOND.[31]

We have seen, in what goes before, how his patient zeal had succeeded in
improving upon these. There was no delay, and no rest. Steadily the art
of making reflectors was urged forward, until he had finally in his
hands the forty-foot telescope.

It must be admitted that this was the limit to which the manufacture of
powerful telescopes could be pushed in his generation. The optical and
mechanical difficulties which prevented a farther advance required time
for their solution; and, indeed, some of these difficulties are scarcely
solved at this day. It may fairly be said that no reflector larger than
three feet in aperture has yet realized our expectations.

_The Improvement of Telescopes and Optical Apparatus._

It will be of interest to give in this place some connected account of
the large forty-foot reflector, of four feet aperture, made by HERSCHEL.
Its history extends from 1785 to 1811. Its manufacture was considered by
his cotemporaries as his greatest triumph. As a machine, it was
extremely ingenious in all its parts, as may be seen from the elaborate
description and plates of it published in the _Philosophical
Transactions_ for 1795. One of its mirrors certainly had good
definition, for, by means of it, the two small satellites of _Saturn_
(_Mimas_ and _Enceladus_) were discovered, and these discoveries alone
would make it famous. Perhaps more was expected of it by the public in
general tha