rding to the depth of
water and weight of moorings, or the importance of the danger. Buoys are
moored with specially tested cables; the eye at the base of the buoy is of
wrought iron to prevent it becoming "reedy" and the cable is secured to
blocks (see ANCHOR) or mushroom anchors according to the nature of the
ground. London Trinity House buoys are [v.04 p.0808] built of steel, with
bulkheads to lessen the risk of their sinking by collision, and, with the
exception of bell buoys, do not contain water ballast. In 1878 gas buoys,
with fixed and occulting lights of 10-candle power, were introduced. In
1896 Mr T. Matthews, engineer-in-chief in the London Trinity Corporation,
developed the present design (fig. 12). It is of steel, the lower plates
being 5/8 in. and the upper 7/16 in. in thickness, thus adding to the
stability. The buoy holds 380 cub. ft. of gas, and exhibits an occulting
light for 2533 hours. This light is placed 10 ft. above the sea, and, with
an intensity of 50 candles, is visible 8 m. It occults every ten seconds,
and there is seven seconds' visibility, with three seconds' obscuration.
The occultations are actuated by a double valve arrangement. In the body of
the apparatus there is a gas chamber having sufficient capacity, in the
case of an occulting light, for maintaining the flame in action for seven
seconds, and by means of a by-pass a jet remains alight in the centre of
the burner. During the period of three seconds' darkness the gas chamber is
re-charged, and at the end of that period is again opened to the main
burner by a tripping arrangement of the valve, and remains in action seven
seconds. The gas chamber of the buoy, charged to five atmospheres, is
replenished from a steamer fitted with a pump and transport receivers
carrying indicating valves, the receivers being charged to ten atmospheres.
Practically no inconvenience has resulted from saline or other deposits,
the glazing (glass) of the lantern being thoroughly cleaned when
re-charging the buoy. Acetylene, generated from calcium carbide inside the
buoy, is also used. Electric light is exhibited from some buoys in the
United States. In England an automatic electric buoy has been suggested,
worked by the motion of the waves, which cause a stream of water to act on
a turbine connected with a dynamo generating electricity. Boat-shaped buoys
are also used (river Humber) for carrying a light and bell. The Courtenay
whistling buoy (fig. 13) is actua