Lightships and Lighthouses

by Frederick Arthur Ambrose Talbot

This novel warning was constructed for installation at the mouth of a Swedish river owing to the extreme velocity of the current. Such a boat may be left unvisited for a year if desired.

A different system, which has been adopted widely throughout the East and in Australian waters, is the Wigham petroleum beacon. This system possesses many notable features, the most important being that well-refined petroleum oil is employed. In many parts of the world carbide of calcium is not readily obtainable, and, moreover, is somewhat expensive, whereas, on the other hand, oil is comparatively cheap and available in unlimited quantities. The principle of working is somewhat novel. The wick is not burned in the manner generally followed in regard to lamps—viz., at the end, which within a short time becomes carbonized and brings a marked diminution of the illuminating power—but it is moved so that the same part is not exposed continuously to the action of the heat arising from combustion. It is caused to travel horizontally over a small roller, in a specially-constructed burner, combustion taking place, therefore, on its flat side. It is moved slowly and continuously over this roller, so that it cannot burn through, and in this manner the flame, being constantly emitted from a fresh surface, is of uniform intensity.

THE WIGHAM THIRTY-ONE DAY UNATTENDED PETROLEUM LIGHT.

The type at left shows the lamp carried upon a cast-iron pillar; while on the right it is mounted upon a lattice tower.

The lamp comprises three main parts. There is the lantern, with the lens and the projecting panes of plate-glass, in the focus of which the burner is fixed. Then there is the burning-oil reservoir, which feeds the wick as it moves towards the burner. This reservoir is circular in shape, somewhat shallow, and serves as a deck on which the lantern is built up. The third part is the float cylinder, made of copper, which is attached to the underside of the oil reservoir. This cylinder is filled with oil, which is kept quite distinct from the burning oil, and thereon floats a weighted copper drum, to which one end of the wick is secured by means of a hook. At the lower end of this cylinder is a micrometer valve, which when opened permits the oil to drip away at a certain speed. This causes the float to fall with the oil in the cylinder, and to drag the wick over the burner roller and down the float cylinder after it, so that a fresh surface of the wick is presented continuously for combustion. The lamps themselves may be divided into two broad classes—the single-wick and the three-wick respectively. The latter obviously emits the more brilliant light, and is the type which is coming into more extensive use at the present time. In the latest type a duplex burner is employed, and this has been found to give a very powerful light with a comparatively low oil consumption.

The light is generally carried at the top of a lattice-work steel tower. A support of this character can be taken to pieces, packed within small compass, and transported without difficulty, while erection is simplified and facilitated. Seeing that a large number of these beacons have been erected on headlands along the wildest stretches of the African continent and the loneliest coasts of Australia, where the methods of transport are restricted to coolies or mules, this method of packing is distinctly advantageous. The lamp is secured to the top of the tower, with the float cylinder of the lamp depending from the centre. In this arrangement, as a rule, a small tank is provided into which a drain-pipe empties the oil dropping from the drip-valve. In this way the oil may be drawn off, filtered, and used again in the float cylinder. In some instances the lamp is mounted upon a cast-iron column, in which case the float cylinder and the oil-drip tank are placed within the tube, access thereto being obtained through a door.

The length of service on one charge varies according to the situation of the light. If in a very exposed and inaccessible place, it may be required to burn for two or three months without attention. Taken on the average, however, a monthly charge has been found to offer the greatest advantages. But in some places the longer interval is unavoidable. For instance, the Wigham light which is mounted upon the extremity of the Manora breakwater at Karachi cannot be approached for three months at a time during the monsoon. Under these circumstances a one-hundred-day service is imperative.

The lenses are of the dioptric order, consisting of six elements built up into a strong gun-metal framework. The internal diameter naturally varies with the size and number of the wicks, and ranges from 10 inches for a 1¹/₈ inch single wick, to 15 inches in the case of a 1⁵/₈ inch three-wick lamp. In the larger sizes a curved plate-glass pane is fitted outside the lens as a protection from the action of the weather. These storm-panes are set in copper doors, so that the glasses may be easily cleaned and polished when the lamp is being retrimmed.