Vickipedia

LIGHTING OF BEACONS AND BUOYS AT SEA. The plan hitherto generally in use for illuminating a rock or reef where no light-house could be built is by means of an ‘ apparent light,’ as in the case of a reef at Stornoway (see LIGHTHOUSE). Of late, trial has extensively and successfully been made of electricity for this purpose. At various times since the discovery of the electric light by Sir H. Davy in 1813, suggestions have been made pointing out the advantages which might be derived from its use upon light-houses. It has long been plain, indeed, that for a purpose of this kind it had properties which placed it far in advance of all other lights-such as its near approach to sunlight in brightness, its great power of penetrating fogs, and its total independence of atmospheric air, which enables it to be produced in a vacuum or under water. Unfortunately its production is attended with great trouble; it also requires rare skill to keep it in perfect order, and even where this is at hand, we cannot yet place absolute reliance upon its steadiness. It has nevertheless been in use at Dungeness, in the south of England, since 1863; and has been introduced with success at Souter Point, Tynemouth (1871), at South Foreland (1878), and at the Lizard light-house (1878). It is used also at three French light-houses, at Odessa, and at Port Said at the entrance of the Suez Canal. At Souter Point the rearward rays of the light are reflected downwards, and used as a light in i different direction on a lower level. Whether or not the electric light is to be ultimately adopted for properly constructed lighthouses, there can be little doubt that for the illumination of beacons, where no light-keeper is on the spot, electricity would be a most desirable agent to produce the light. As far as can be at present seen, the ordinary Electric Light (q. v.) may be dismissed as unsuitable for beacons. It will at least require to be greatly simplified before it can be used for such a purpose. In the article INDUCTION OF ELECTRIC CURRENTS will be found a description of the method of producing sparks by means of an induction coil. These sparks can be made to follow each other so quickly as to appear like a flash surrounded by a luminous haze. Taking advantage of this power of electricity, Mr. Thomas Stevenson proposed in 1866 to apply it to the illumination of beacons, and in that year a series of interesting experiments were made at New-haven pier, with the aid of instruments constructed by Mr. Hart of Edinburgh. Although up till this time no further steps have been taken to make practical application of this suggestion, the proposal merits attention for its ingenious application of a scientific fact which had not as yet been successfully put to such a use. In the experiments referred to, the electric current passed through a wire 800 feet long. Suppose a beacon to be situated at some distance from the shore, as shown upon the annexed diagram (fig. 1).

A galvanic battery, consisting of, say, six Bunsen cells, is placed at B in a house upon the shore. From this, the electrical current is conveyed along a submarine cable to the beacon, and returns by earth-plates at E, E, in the usual manner, to complete the circuit; its course being indicated on the diagram by arrows. The induction coil is placed upon the beacon at C. and properly connected with the conducting wire of the cable, so as to make the current generated by the battery traverse its primary coil. A wire from each end of its secondary coil is then conveyed to the focus of the optical apparatus, the ends of the two wires being here brought within half-an-inch of each other, and furnished with indestructible points of platinum. The induced or secondary current, in crossing this narrow space, produces the succession of sparks which constitute the light, but as explained under the head INDUCTION OF ELECTRIC CURRENTS, it only does so at the moment the current is interrupted or broken. It is consequently necessary to have some means of completing and breaking the galvanic circuit in rapid alternations, so as to produce the flashes in quick succession. The break for this purpose is placed at I, near the battery.

In the experiments now described, a great deal was found to depend upon the peculiar way the current was broken. None of the breaks in use giving a successful result, Mr. Halt devised a new one of an ingenious construction, which produced a more constant and powerful light. Fig. 2 shows this instrument.

The difference between it and other mercury or spring breaks lies in the fact, that with them the current is off and on for nearly equal spaces of time; but this one is so contrived that the wire at a is three times longer in the mercury, J, than it is out of it; consequently, the current is three times longer on than it is off, and so-allows the soft iron core of the induction coil to be more fully magnetized. The result of this is a secondary current of comparatively high intensity, and of course the production of more brilliant sparks between its two terminals. We may explain, that the moment the wire at a touches the mercury, the current passes and the moment it is removed the current stops-the direction it takes being indicated in the figure by the arrows. The wire at ” alternately dips and rises by the action of an ordinary electromagnet, EE, turning the crank e; the second bottle of mercury is not used to break contact, but only to continue the current, for which a spring would answer as well.

By the use of more than one induction coil, the light could be materially increased, so that there seemed a likelihood of being able to produce it powerful enough to be seen at the distance of a few miles. Another method of lighting buoys as well as beacons without the aid of electricity has lately been shown to be practicable. Coal or other inflammable gas can be so compressed that a buoy may be made to receive at once and store up as much condensed gas as will suffice to keep a steady flame burning for a month or more. Gas for this purpose can be economically manufactured from some of the waste products of shale-oil works. Mr. Stevenson has also suggested the employment of electricity to ring bells, so as to give warning to sailors in foggy weather.