n of the sea-water from acting upon the iron. This course of
granite is grooved to receive the flange of the lower plates of the
tower, from which lightning-conductors are to be continued to the sea.
The tower is of course itself a lightning-conductor of the best kind.
The diameter of the tower-shaft is eighteen feet six inches at its
base, diminishing to eleven feet under the cap; it is formed of nine
tiers of plates each ten feet in height, varying from one to three
quarters of an inch thick. The circumference is formed of eleven
plates at the base, and nine at the top: they are cast with a flange
all round the inner edges; and when put together these flanges form
the joints, which are fastened together with nut and screw-bolts, and
caulked with iron cement. The cap consists of ten radiating plates,
which form the floor of the light-room; they are screwed to the tower
upon twenty pierced brackets, and are finished by an iron railing.
The lower portion, namely, twenty-seven feet, is filled up with
masonry and concrete, weighing about three hundred tons, and so
connected with the rock itself as to form a solid core of resistance.
The remaining portion of the building is divided into store-rooms and
berths for the attendants in the lighthouse.

The light-room consists of cast-iron plates five feet high, on which
are fixed metal sash-bars filled with plate-glass; these, terminating
with a point, are covered with a copper roof, whence rises a short
lightning-rod, trebly gilt at the point. The light is of the revolving
kind, consisting of fifteen Argand lamps and reflectors, five in each
side of an equilateral triangle, and so placed as to constitute a
continuous light, but with periodical flashes. The Admiralty notice
which announced the light for exhibition on the 1st November, 1842,
states that the centre of the light is ninety-six feet above the level
of the sea, and in clear weather the light can be seen from a distance
of twenty-one miles.

To preserve as low a temperature as the circumstances and climate will
permit, the iron shell was lined with a non-conducting material, as
slate or wood, leaving an annular interstice, through which a constant
ventilation is effected, so as to carry off the excessive heat.

To preserve the two lower tiers from rusting, they are coated with
coal-tar. The tower itself is painted white. The only brasing which
has been thought necessary is a few cross tiers at each horizontal
joint,