e reflectors originally employed were casts in plaster of Paris,
from a mould formed to the parabolic curve, and lined with facets of
mirror-glass. The power of these reflectors, however, was
comparatively small, from the reflecting surface being composed of
numerous pieces, in each of which only one point coincided with the
curve of the parabola.

The Trinity House having been at great pains to improve the reflecting
apparatus on the coast of England, with the advice and assistance of
eminent scientific men, adopted parabolic reflectors made of silvered
copper; and these, from their superior effects, have ultimately been
introduced into all the lighthouses of the united kingdom. In the
northern lighthouses, the reflectors consist of copper coated with
silver, in the proportion of six ounces of silver to one pound
avoirdupois of copper, which are rolled together, and then, with much
labour and great nicety, by a process of hammering and polishing,
formed to the parabolic curve of a mould made with mathematical
precision. The focal distance of the curve is four inches. The diagram
for the Bell-Rock reflectors was drawn by Professor Leslie, and the
mould was made by Mr. Adie the optician. The powers of this elegant
production of the mechanical art are said to be quite astonishing; and
by comparing its highly-polished and regularly-curved surface with the
previous glass reflector, the superiority of the former seems to be
immense: indeed, its influence extends to the horizon formed by the
height of the lighthouse-tower and the earth's curvature. The
reflectors in general use measure over the tips twenty-one inches as
applicable to stationary, and twenty-live inches for revolving lights.

The Catoptric or reflecting system was first adopted under the
direction of Borda, at the Corduan Lighthouse, probably about the year
1780. The system was soon introduced into England; and one of the
first acts of the Northern Lights' Board, so early as 1786, was to
substitute reflectors in place of coast-lights, which till then had
been the only beacons on the Scotch coast.

In the improved lights the best spermaceti oil and the Argand lamp
have been introduced. The keepers are professionally adepts in the
management of lamps; and should a drop of oil be spilt, the floor is
covered with painted floorcloth to receive it. The Argand lamp-burners
are tipped with silver, to prevent the waste and imperfection to which
copper is subject, fro