used for the mirror is of a more tractable description than the
metallic substance which was employed by Herschel and by Lord Rosse.
A reflecting telescope of the present day would not be fitted with a
mirror composed of that alloy known as speculum metal, whose
composition I have already mentioned. It has been found more
advantageous to employ a glass mirror carefully figured and polished,
just as a metallic mirror would have been, and then to impart to the
polished glass surface a fine coating of silver laid down by a
chemical process. The silver-on-glass mirrors are so much lighter
and so much easier to construct that the more old-fashioned metallic
mirrors may be said to have fallen into almost total disuse. In one
respect however, the metallic mirror may still claim the advantage
that, with reasonable care, its surface will last bright and
untarnished for a much longer period than can the silver film on the
glass. However, the operation of re-silvering a glass has now become
such a simple one that the advantage this indicates is not relatively
so great as might at first be supposed.

[PLATE: STREET VIEW, HERSCHEL HOUSE, SLOUGH.]

Some years elapsed after Herschel's attention had been first directed
to astronomy, before he reaped the reward of his exertions in the
possession of a telescope which would adequately reveal some of the
glories of the heavens. It was in 1774, when the astronomer was
thirty-six years old, that he obtained his first glimpse of the stars
with an instrument of his own construction. Night after night, as
soon as his musical labours were ended, his telescopes were brought
out, sometimes into the small back garden of his house at Bath, and
sometimes into the street in front of his hall-door. It was
characteristic of him that he was always endeavouring to improve his