A NINETY MILLION CANDLE POWER ELECTRIC BEACON
A truly gigantic electric light beacon, shown in the accompanying illustrations, is just now being made the subject of a series of tests at the United States Lighthouse Depot, at Tompkinsville, Staten Island, N.Y. It was manufactured by Henri Lepaute, of Paris, and was first exhibited at the Chicago World’s Fair and subsequently at Atlanta and Nashville. It consists of two great lenses, each 9 feet in diameter, between which, in their focus, is placed a 9,000 candle power arc light. The valves and the light are carried by a vertical shaft which terminates at its lower end in a hollow drum, which latter floats in a bath of mercury. The great weight of the lantern, estimated at several tons, is thus carried by the mercury, and friction is reduced to such a point that the whole mass may easily be rotated by the pressure of one’s finger.
Each lens consists of a set of lenses and prismatic segments, which are built up concentrically within a stout framework of brass, into which the segments are carefully cemented. The center of the lens consists of a solid disk. Surrounding this are eight concentric prisms, whose edges are in contact, and surrounding these are fourteen larger prisms, making 190 separate segments in the whole lens. The angles of the prisms are such that the rays of light are refracted so as to leave the lens in parallel non-divergent rays, and it is estimated that the 9-foot beam of light thus projected is of 90,000,000 candle power. The lantern is rotated by means of the clockwork which will be noticed at the right hand side of the framework. As there are two beams of light and the period of rotation is 10 seconds, every part of the horizon receives a flash once in 5 seconds, the duration of the flash being about one-twelfth of a second.
The illumninant is an arc lamp of 9,000 candle power, which is so constructed that the arc will always remain in the exact focus of the lenses, the latter being so placed that their foci coincide. The maintenance of the arc in a fixed position is secured by connecting the carbon holders so that they both travel simultaneously and at the same speed, as the carbon points are burnt away. The carbons are fed together by the clockwork enclosed in the base of the lamp. The mechanism is controlled by an electromagnet arranged in shunt around the arc. As the carbons are burnt away the resistance of the arc increases and the magnet releases the clockwork escapement, permitting it to bring the carbons together. The feed is slow and frequent, maintaining the arc at a practically uniform length.
The carbons vary in size from ⅝ to 2 inches diameter, and the 55-volt current will vary from 25 to 100 amperes, according to the carbons used. The current will be furnished by an alternating generator made by the General Electric Company, driven by a 25 horse power Ideal engine, steam being supplied by a 25 horse power Fitzgibbon’s boiler. When the lens is installed at a station the steam and electric plant will be furnished in duplicate, so that, should one set be disabled, the other can be brought at once into use.
As a precaution against the extinction of the light through the failure of the lamp, the whole lamp with its mechanism is provided in duplicate, the two lamps being carried at each side of a turntable, which is a permanent fixture within the bivalve lens. The turntable is placed to the left of the common focus of the lenses in such a position that on rotating it either of the lamps may be brought at will into the focus. The lamps are carried on a sliding rest on the turntable, and by means of an endless screw operated by a handwheel on the outside of the lenses they may be drawn out for inspection or repairs.
The theoretical luminous range of this giant lens in clear weather is 146.9 nautical miles ; and if the light were placed on a sufficiently lofty eminence to compensate for the curvature of the earth, it would be possible, under favorable circumstances, to see it at this distance. The geographical range, as it is called, depends on the height of the focal plane above the sea level. If the light were to be installed at Barnegat, where the height of the focal plane is 165 feet, the light would be visible from a vessel’s deck at a height of say 15 feet above the water at a distance of 19 nautical miles in clear weather, and, on account of its great power, at the same distance in hazy weather.
In a dense fog, however, even such a great light as this would be practically extinguished. In this latitude the light may be expected to be seen to the limit of the geographical range for 330 nights out of the year.
The present tests are being carried out by Lieut. Col. D. P. Heap, Corps of Engineers, U. S. A., engineer of the Third Lighthouse District, to whom we are indebted for particulars and photographs used in the preparation of the present article.