Engineering Wonders of the World
Volume I
Forfatter: Archibald Williams
År: 1945
Serie: Engineering Wonders of the World
Forlag: Thomas Nelson and Sons
Sted: London, Edinburgh, Dublin and New York
Sider: 456
UDK: 600 eng - gl.
Volume I with 520 Illustrations, Maps and Diagrams
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THE STORY OF THE LIGHTHOUSE.
The Story
of the
Bishop Rock
Lighthouses.
Scilly Islands, the Bishop
Rock was for centuries a
perilous ob-
stacle, scarce-.
ly discernible
above the
face of the
sea, and dreaded by mariners
of all nations. The rock is
of a conical form, somewhat
like that of a bishop’s mitre,
surrounded by deep water,
and exposed to the full swell
of the Atlantic, with a
“ fetch ” of four thousand
miles. Up to the year 1790
the rock-bound coast of the
Scilly Islands was lighted by
nothing better than an open
coal fire at the top of a tower
on the island of St. Agnes,
several miles within the dan-
gerous outer reef of water-
washed rocks. The fatal
disaster which befell Sir
Cloudesley Shovel in 1707
when returning from Toulon
with his fleet may have sug-
gested anew the necessity for
more efficient danger signals,
but, owing to the slow devel-
opment of lighthouse design,
nothing more was done until
1790, when the Corporation
of Trinity House installed in
St. Agnes a revolving oil
light, with “ catoptric ” or reflecting mirrors
—the first of its kind on the coast-line
of the United Kingdom. Even this light
was not an efficient warning for ships beyond
the outer reef, and in 1846 the Trinity
House authorities at last decided to erect on
the Bishop Rock a lighthouse with a fixed
light of 6,500 candle power, and a range of
about 17 miles. At low-water level the rock is
Fig; 17.—APPROXIMATE FORM OF BISHOP ROCK. (THE INSET
SHOWS ROCK WITH LIGHTHOUSE BUILT.)
.......................................................-................................. -....................................:...................... .................................. ■
only 153 feet long by 52 feet wide, and de-
scends almost sheer to a depth of from 120
feet to 150 feet. Fig. 17 is a sketch showing
approximately the form of the Bishop Rock,
itself a natural tower of very hard granite.
From this sketch it will be realized why, in
1845, it was thought that the width of the
rock was inadequate to provide a safe resting-
place for the base of a masonry tower exposed