LIGHTING or BEACONS A.ND BUOYS AT SEA. TI1C plan hitherto generally in U£C 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 LIGHT-HOUSE). 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 II. Davy in 1813, sugges tions have been inade 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, ancl 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 s. of England, since 1862; and has beet, introduced with success at Scatter point, Tynemouth (1871), at South Foreland (1873), 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 a different direction on a lower level. Whether or not the electric light is to be ultimately adopted for properly constructed light-houses, there can be little doubt that for the illumination of beacons, where no light-keeper is on the spot, elec tricity 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 siinplified before it can be used for such a purpose. In the article INDUCTION OF ELECTRIC CURRENTS will lie found a description of the method of producing sparks bymeans 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 y-ear a series of interest ing experiments were made at Newhaven pier, with the aid of instruments constructed by Mr. Hart of Edinburgh. Although up to 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 ft. long. Suppose a beacon to be situated at some distance from the shore, as shown upon the annexed diagram. 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 con veyed 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 diag,ram by atTows. 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 . ofricatnheeoaichticaeinadppolfwaittsussetchoenetina(cys coil is then conveyed to the focus AUL.
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\ s's'‘.,,,,,,-"\Q:, • ;. n=",..4i ::. -40:iyi' Aar -4---- s's.. --.1,., ' .'" ' 'kl\ The induced or secondary current, in crossing this narrow space, pro duces the succession of sparks which constitute the light, but, as explained under the head INDUC