Second and third order lights are employed to mark Hie secondary
capes, islands, rocks, reefs and sand-bars embraced between the
more prominent headlands, while lights of inferior order desi^rnate
the entrances to harbors and channels, and vary in intensity accord-
ing to the distance at which they should be seen. These are general
principles, but geographical reasons prevent them from being applied
rigorously.
LONG8HIP8 AND WOLF ROCK.
In 1795 a light-house on Longships Rock and beacons on the
Wolf and Rundlestone were erected in order to mark the danjrers
of the coast near Land's End, England. In 1841 a U<;ht-ship was



58 ANCIENT AND MODERN LIGHT-HOUSES.
moored in forty fathoms of water off the Sevenstones Rocks, midwaj*
between the Land's End and Scilly. These were all works of con-
siderable difficulty.
The Longships' light-house is a granite structure, but as the light
is only seventy-nine feet above high water of spring tides, the lantern,
owing to the terrific seas, was so much under water during stormy
weather, that it was difficult to determine the character of the light.
As it was not considered safe to raise the tower to a sufficient
height to render the lantern safe from the heaviest seas, it was deter-
mined to replace it by a granite column one hundred and ten feet
above the water. The work was commenced in 1869 and was com-
pleted, with the exception of setting the lens, in 1873.
There is an arrangement for marking the dangers of the Rund?c-
stone Rocks to the southward and the Brissons Rocks to the north-
ward, by sections of red light. As these rocks are well out from
land they were great dangers to navigators.
