The first lighthouse erected there was begun in 1847 under the
direction of N. Douglass. The tower consisted of a cast and wrought
iron openwork structure having the columns deeply sunk into the
rock. On the 5th of February 1850, when the tower was ready for
the erection of the lantern and illuminating apparatus, a heavy
storm swept away the whole of the structure. This tower was designed
for an elevation of 94 ft. to the focal plane. In 1851 the
erection of a granite tower, from the designs of James Walker, was
begun; the light was first exhibited in 1858. The tower (fig. 11)
had an elevation to the focal plane of 110 ft., the lower 14 courses
being arranged in steps, or offsets, to break up the force of the waves.
This structure also proved insufficient to withstand the very heavy
seas to which it was exposed. Soon after its completion the 5-cwt.
fog bell, fixed to the lantern gallery 100 ft. above high-water mark,
was washed away, together with the flagstaff and ladder. The
tower vibrated considerably during storms, and it was found that
some of the external blocks of granite had been split by the excessive
stress to which they had been exposed. In 1874 the tower was
strengthened by bolting continuous iron ties to the internal surfaces
of the walls. In 1881, when further signs of damage appeared, it
was determined to remove the upper storey or service room of the
lighthouse, and to case the structure from its base upwards with
granite blocks securely dovetailed to each other and to the existing
work. At the same time it was considered advisable to increase the
elevation of the light, and place the mean focal plane of the new
apparatus at an elevation of 146 ft. above high-water mark. The
work was begun in 1883, and the new apparatus was first illuminated
on the 25th of October 1887. During the operation of heightening
the tower it was necessary to install a temporary light, consisting
of a cylindrical lightship lantern with catoptric apparatus; this was
raised from time to time in advance of the structure as the work
proceeded. The additional masonry built into the tower amounts
approximately to 3220 tons. Profiting by the experience gained
after the construction of the new Eddystone tower, Sir J. N. Douglass
decided to build the lower portion of the improved Bishop Rock
tower in the form of a cylinder, but with considerably increased
elevation (figs. 12 and 13). The cylindrical base is 40 ft. in diameter,
and rises to 25 ft. above high-water mark. The lantern is cylindrical
and helically framed, 14 ft. in diameter, the glazing being 15 ft. in
height. The optical apparatus consists of two superposed tiers of
lenses of 1330 mm. focal distance, the lenses subtending a horizontal
angle of 36° and a vertical angle of 80°. The apparatus consists of
5 groups of lenses each group producing a double flashing light of one
minute period, the whole apparatus revolving once in five minutes.
The maximum aggregate candle-power of the flash is 622,000 candles.
A gun-cotton explosive fog signal is attached to the lantern. The cost
of the various lighthouses on the Bishop Rock has been as follows:
| 1. Cast iron lighthouse | £12,500 | 0 | 0 |
| 2. Granite lighthouse | 34,559 | 18 | 9 |
| 3. Improved granite lighthouse | 64,889 | 0 | 0 |
The Smalls Lighthouse.—A lighthouse has existed on the Smalls rock, 1812 m. off Milford Haven, since 1776, when an oak pile structure was erected by Henry Whiteside. The existing structure, after the model of the second lighthouse on the Bishop Rock, was erected in 1856–1861 by the Trinity House and is 114 ft. in height from the foundation to the lantern floor. A new optical apparatus was installed in 1907.
Minot’s Ledge Lighthouse.—The tower, which is 89 ft. in height, is built of granite upon a reef off Boston Harbor, Mass., and occupied five years in construction, being completed in 1860 at a cost of £62,500. The rock just bares at low water. The stones are dovetailed vertically but not on their horizontal beds in the case of the lower 40 ft. or solid portion of the tower, bonding bolts being substituted for the horizontal dovetailed joints used in the case of the Wolf and other English towers. The shape of the tower is a conical frustum.
Wolf Rock Lighthouse.—This much exposed rock lies midway between the Scilly Isles and the Lizard Point, and is submerged to the depth of about 6 ft. at high water. The tower was erected in 1862–1869 (fig. 14). It is 116 ft. 6 in. high, 41 ft. 8 in. diameter at the base, decreasing to 17 ft. at the top. The walls are 7 ft. 912 in. thick, decreasing to 2 ft. 3 in. The shaft is a concave elliptic frustum, and contains 3296 tons. The lower part of the tower has projecting scarcements in order to break up the sea.
Dhu Heartach Rock Lighthouse.—The Dhu Heartach Rock, 35 ft. above high water, is 14 m. from the island of Mull, which is the nearest shore. The maximum diameter of the tower (fig. 15), which is of parabolic outline, is 36 ft., decreasing to 16 ft.; the shaft is solid for 32 ft. above the rock; the masonry weighs 3115 tons, of which 1810 are contained in the solid part. This tower occupied six years in erection, and was completed in 1872.
Great Basses Lighthouse, Ceylon.—The Great Basses lighthouse lies 6 m. from the nearest land. The cylindrical base is 32 ft. in diameter, above which is a tower 67 ft. 5 in. high and 23 ft. in diameter. The walls vary in thickness from 5 ft. to 2 ft. The tower, including the base, contains about 2768 tons. The work was finished in three years, 1870–1873.
Spectacle Reef Lighthouse, Lake Huron.—This is a structure similar to that on Minot’s ledge, standing on a limestone reef at the northern end of the lake. The tower (fig. 16) was constructed with a view to withstanding the effects of ice massing in solid fields thousands of acres in extent and travelling at considerable velocity. The tower is in shape the frustum of a cone, 32 ft. in diameter at the base and 93 ft. in height to the coping of the gallery. The focal plane is at a level of 97 ft. above the base. The lower 34 ft. of the tower is solid. The work was completed in 1874, having occupied four years. The cost amounted to approximately £78,000.
Chicken Rock Lighthouse.—The Chicken Rock lies 1 m. off the Calf of Man. The curve of the tower, which is 123 ft. 4 in. high, is hyperbolic, the diameter varying from 42 ft. to 16 ft. The tower is submerged 5 ft. at high-water springs. The solid part is 32 ft. 6 in. in height, weighing 2050 tons, the whole weight of the tower being 3557 tons. The walls decrease from 9 ft. 3 in. to 2 ft. 3 in. in thickness. The work was begun in 1869 and completed in 1874.
Ar’men Lighthouse.—The masonry tower, erected by the French Lighthouse Service, on the Ar’men Rock off the western extremity of the Île de Sein, Finistère, occupied fifteen years in construction (1867–1881). The rock is of small area, barely uncovered at low water, and it was therefore found impossible to construct a tower having a base diameter greater than 24 ft. The focal plane of the light is 94 ft. above high water (fig. 17).
St George’s Reef Lighthouse, California.—This structure consists of a square pyramidal stone tower rising from the easterly end of an oval masonry pier, built on a rock to a height of 60 ft. above the water. The focal plane is at an elevation of 146 ft. above high water. The site is an exceedingly dangerous one, and the work, which was completed in 1891, cost approximately £144,000.
Rattray Head Lighthouse.—This lighthouse was constructed between the years 1892 and 1895 by the Northern Lighthouse Commissioners upon the Ron Rock, lying about one-fifth of a mile off Rattray Head, Aberdeenshire. The focal plane is 91 ft. above high water, the building being approximately 113 ft. in height. In the tower there is a fog-horn worked by compressed air.
Fastnet Lighthouse.—In the year 1895 it was reported to the Irish Lights Commissioners that the then existing lighthouse on the Fastnet Rock off the south-west coast of Ireland, which was completed in 1854 and consisted of a circular cast iron tower 86 ft. in height on the summit of the rock, was considerably undermined. It was subsequently determined to proceed with the erection of a granite structure of increased height and founded upon a sound ledge of rock on one side of the higher, but now considerably undermined.
