CHAPTER XVII

THE MOST POWERFUL ELECTRIC LIGHTHOUSES OF THE WORLD

In a previous chapter I have mentioned that, although oil is the most popular form of illuminant in lighthouse engineering, electricity is maintained to be preferable, but labours under one heavy disadvantage which militates against its more general adoption. It is expensive to install and to maintain. Under these circumstances the system has been restricted to lights of the most important character, preferably landfalls or beacons indicating the entrance to a harbour. Thus, we have the Lizard at the entrance to the English Channel; St. Catherine’s on the Isle of Wight; the Rothersand at the entrance to the Weser; the Heligoland flaring over the island of that name; the Isle of May at the entrance to the Firth of Forth; Cape Héve near Havre; and the Navesink light on the highlands of the New Jersey coast, to guide the mariner into New York harbour.

The first attempt to apply electricity to lighthouse illumination was made in the year 1859, by the Trinity Brethren, on the strong recommendations of Professor Faraday, who was then scientific adviser to the British lighthouse authorities. The South Foreland light was selected for the experiments, and the magneto-electric machine invented by Professor Holmes, who subsequently perfected the siren, was used.

The installation was built with extreme care, as the imperative necessity of reliability, owing to the peculiar nature of the application, was recognized very fully. The large wheels made eighty-five revolutions per minute, and at this speed produced a very steady light. On a clear night, owing to the elevation of the cliff the light was visible for over twenty-seven miles, and could be descried readily from the upper galleries of the lighthouses on the opposite French shore. In order to determine the relative value of electric lighting in comparison with the other methods of illumination then in vogue, another light emitted by an oil-lamp, with reflectors characteristic of the period, was burned simultaneously from a point below the top light, so that passing mariners were able to compare the two systems of illumination under identical conditions.

The French lighthouse authorities were not dilatory in adopting the new idea, and electricity was installed in the Cape Héve lighthouse in 1863. The light was brilliant for those times, being approximately of 60,000 candle-power. The French investigators then embarked upon an elaborate series of experiments, and in 1881 an electric light of about 1,270,000 candle-power was established at the Planier lighthouse, near Marseilles. The investigations culminated in the great achievement of M. Bourdelles, who, while engineer-in-chief of the Service des Phares, designed a new electric installation for the Cape Héve light, of 25,000,000 candle-power.

Meantime British engineers had not been idle. In 1871 Messrs. Stevenson, the engineers-in-chief to the Commissioners of Northern Lighthouses, advocated strongly the establishment of an electric light upon the Scottish coast; but it was not until 1883 that the Board of Trade sanctioned the sum necessary to complete such an enterprise, and suggested that the innovation should be made at the Isle of May lighthouse, as being the most important on the East Scottish coast.

This is one of the historic light-stations of Scotland. Lying in the Firth of Forth, five miles off the Fifeshire shore, the islet obstructs a busy marine thoroughfare. For 276 years a light has gleamed from its summit, the change from the coal fire to Argand lamps with reflectors having been made by Thomas Smith, the first engineer to the Commissioners of Northern Lighthouses, when this body assumed its control in 1816. Twenty years later it was converted to the dioptric system, with a first-order fixed light apparatus having a four-wick burner. This arrangement was in service for half a century, when it was converted to electricity in conjunction with a dioptric condensing apparatus.

The electric installation was designed throughout by Messrs. Stevenson, and it possesses many ingenious and novel features to this day, while it was the pioneer of modern electric lighting systems as applied to lighthouse engineering. Although marked improvements have been effected in electrical engineering and science since its completion, it still ranks as one of, if not the, most powerful electric lighthouses in the world. The beacon is a prominent edifice on the summit of the island. The building is somewhat pretentious, rather resembling a battlemented castle than a warning for the mariner, the optical apparatus being housed in a square turret rising above the main part of the building. When electric illumination was adopted, the existing accommodation for three keepers was found insufficient, while a generating-station was necessary. Instead of extending the old building to accommodate the additional facilities, a second station was built at a low-lying point near the sea-level. This contains the engine and generating house, together with quarters for three more keepers and their families. This decision was made because at this point, 810 feet away and 175 feet below the lighthouse, there is a small fresh-water loch whence water is available for the boilers and condensers, while a marked saving in the cost of handling fuel as well as of the haulage of the building materials and machinery was feasible. The current is led from the power-house to the lighthouse by means of overhead copper conductors.

Some difficulty was experienced in securing electrical apparatus suited to the searching exigencies of lighthouse engineering, and the designers made one stipulation, which at first appeared to baffle fulfilment. This was the placing of the positive carbon below, instead of above, so as to enable the strongest light to be thrown upwards, to be dealt with by the upper part of the dioptric apparatus, whereby it could be used more effectively. One firm struggled with this problem for many months, and then was compelled to admit defeat, as time for further experimenting was unavailable, since the lighthouse was almost completed. Accordingly, the designing engineers had to revise their plans, and had to acquire alternate-current De Meriten machines, which, although more expensive and less powerful than those originally intended, yet were, and are still, wonderfully steady in working, while they had previously proved highly efficient for lighthouse service. Two generators of this description were secured, and they constituted the largest that had been made up to this period, each plant weighing about 4½ tons. Each machine has sixty permanent magnets, disposed in five sets of twelve each, while each magnet is made up of eight steel plates. The armature makes 600 revolutions per minute, and develops an average current of 220 ampères.

The installation is so designed that one-, two-, three-, or four-fifths, or the whole, of the current can be sent from each unit to the distributor for transmission to the lantern, or the two machines may be coupled and the full current from both utilized. The current is conveyed to the lantern through copper rods 1 inch in diameter, and this was the first occasion on which such conductors were utilized for lighthouse work. There are three lamps of a modified Serrin-Berjot type, one being in service, and the other two held in reserve. By means of a by-pass, or shunt, a large percentage of the current is sent direct to the lower carbon, only a sufficient amount to regulate the carbons being sent through the lamp. The carbons used are about 1½ inches in diameter, though two-inch carbons can be employed when both machines are running, and the rate of consumption is 1¼ inches, or, including waste, 2 inches, per hour. The power of the arc thus obtained with the current fed from one generator is between 12,000 and 16,000 candles. In the event of the electric installation breaking down, a three-wick paraffin oil lamp is kept in reserve, ready for instant service, and it can be brought into use within three minutes.

The dioptric apparatus, designed by Messrs. Stevenson, and manufactured by Messrs. Chance Brothers and Co. of Birmingham, is of a novel character, inasmuch as the condensing principle has been carried to a pronounced degree. The light characteristic is four brilliant flashes in quick succession every thirty seconds. The lenticular apparatus also includes the ingenious idea advocated by Mr. Thomas Stevenson, an earlier engineer-in-chief to the Northern Commissioners and perhaps the greatest authority on lighthouse optical engineering, whereby the light may be dipped during a fog. Thus, in clear weather the strongest part of the ray may be directed to the horizon, while in thick weather it can be brought to bear upon a point, say, four or five miles away. The flashes are produced by a revolving cage of straight vertical prisms, which enclose the fixed-light apparatus. This cage makes one complete revolution every minute, the rotary movement being secured through a train of wheels and a weight, which has a fall of 60 feet in a tube extending vertically through the centre of the tower, the mechanism being wound up once an hour by manual effort.

The beam of light obtained by the aid of electricity is of intense brilliancy and penetration. Its equivalent in candle-power is somewhat difficult to determine, because the methods of calculation are somewhat arbitrary and misleading. By their own method of calculation, the engineers responsible for the installation rate it at 3,000,000 candle-power with one generator in use, and 6,000,000 candle-power when both are going. This is from 300 to 600 times as intense as the oil light which was superseded. By another method of calculation the beam is of 26,000,000 candle-power, while another principle of rating brings it to upwards of 50,000,000 candle-power. In clear weather the light has a range of twenty-two miles, being indistinguishable at a greater distance, owing to the curvature of the earth; but the flashes of light illuminating the clouds overhead may be picked up forty or fifty miles away. The total cost of electrifying the Isle of May light was £15,835, or $79,175; while the annual cost of maintenance is over £1,000, or $5,000.

The most famous English electric lighthouse is that of St. Catherine’s, in the Isle of Wight. This point, like the Isle of May, has been a beacon for centuries. Its creation for this work even antedates its northern contemporary, because in the fourteenth century a chantry was built by a benevolent knight on the highest point of St. Catherine’s Downs, who furthermore provided an endowment for a priest “who should chant Masses and maintain a burning light at night for the safety of mariners.” But this protection fell into desuetude.

The station, however, was revived upon the old site in 1785, but it had to be abandoned, because it was found to be built at too high an elevation. It was so often enveloped in fog as to be useless, or at least unreliable, to the seafarer. A new tower, accordingly, was erected at a lower level, and brought into service in 1840, the warning rays being thrown from a height of 134 feet above the water. Oil was used with a burner of six rings, the light being officially known as a “fixed oil light of the first class,” while the beam was diffused over an arc of 240 degrees. In the middle eighties the Brethren of Trinity House decided to bring it up to date, and selected electricity as the illuminant, at the same time changing the light from the fixed to the revolving class, with a five-second flash once every thirty seconds.

The installation is not widely dissimilar from that used at the Isle of May. It comprises two De Meriten dynamos in duplicate, while the lamps are of the modified Serrin-Berjot type, using carbons, not of circular section, but with fluted sides. This shape was introduced by Sir James Douglass, who contended that the former type did not produce the requisite candle-like steadiness of the flame so essential to lighthouse illumination. The dioptric apparatus was of the sixteen panel type, so that the rays were thrown out in sixteen brilliantly white horizontal spokes. To one approaching the lighthouse at night-time, the effect in the sky was somewhat curious. It recalled a huge and illuminated cart wheel or Catherine wheel, lying flat on its side, throwing its rays to all points of the compass in a steadily moving circle. This practice had been borrowed from the French, who went so far as to introduce a twenty-four panel system, and, as in France, the St. Catherine’s light, when first brought into service, was not a complete success. The French considered that, by distributing the light through as many panels as possible, the question of bringing the flashes into action at short intervals would be facilitated, ignoring the fact that by so doing the intensity of each ray was impoverished. In other words, with the twenty-four panel light each panel only received and threw out one-twenty-fourth part of the volume of light emitted by the arc. Similarly, in the St. Catherine’s light only one-sixteenth part of the light produced was thrown through each panel. A few years ago the optical system was replaced by an apparatus having fewer panels. The light thrown from the Isle of Wight pharos, with its beam exceeding 5,000,000 candle-power, represents a marked advance upon the oil light which it displaced, and certainly it ranks as the most brilliant light in the English Channel.

A few years ago another magnificent light was brought into service in the North Sea by the installation of electricity in the lighthouse of Heligoland. With characteristic Teuton thoroughness, the Germans discussed the question of the illuminant for this beacon in all its bearings, and resolved to introduce the most powerful light possible. This decision was influenced by the dangerous character of the waters washing the island, as it is flanked on all sides by highly perilous ridges and sandbanks, which must become accentuated owing to the heavy sea-erosion that prevails.

The German authorities investigated the various electrical installations that had been laid down for lighthouse work, with a view to discovering the most suitable system, the advantages and defects of existing electric lights, and how the drawbacks might be overcome most successfully. Meantime the famous Siemens firm discovered a means of grinding glass mirrors into parabolic form, and this discovery was accepted as the solution to the problem.

In this type of mirror the back is silvered. The metallic polished surface is protected completely from mechanical injury and from all possibility of tarnishing. The inventors claim that mirrors so prepared are able to compete successfully with lenses and totally reflecting prisms--in fact, it was maintained that the silvered glass parabolic mirror possessed the advantages of greater reflecting power and enhanced accuracy, with less divergence of the beam of light.

Owing to the perfection of the lenses and prisms system of lighthouse optics, the introduction of arc lights in conjunction with parabolic mirrors was received with considerable hesitation. In order to dispel these doubts, the above-mentioned firm forthwith embarked upon an elaborate series of comparative tests at Nuremberg to ascertain the relative value of the two systems, and as a result of these experiments they concluded that quite as good an effect is obtainable with the arc and parabolic mirror as with the best examples of any other method.

Accordingly, the authorities decided to install the system in the Heligoland lighthouse. They stipulated that the intensity of the beam of light should be at least 30,000,000 candle-power, with a maximum current of 100 ampères. The duration of the flash was to be one-tenth of a second, followed by eclipses of five seconds’ duration.

The electrical engineering firm entrusted with the contract fulfilled these conditions by mounting three searchlights spaced 120 degrees apart upon a rotating platform. That is to say, each light is projected outwards from a point equal to a third of the circumference of a circle. The mirror diameter was settled at 75 centimetres (29½ inches) and the focal length at 250 millimetres (10 inches), the current being taken at 34 ampères when the table made four revolutions per minute.

Subsequently a fourth searchlight was introduced into the apparatus, for the purpose of practical experiments and observations concerning the duration of the light-flash. This fourth unit was mounted above the three searchlights, but in the axis itself. It is so disposed that its flash comes midway between any of the two below, and it is arranged to rotate three times as quickly as the main group of lights. Accordingly, the duration of the flash thrown from the fourth searchlight is only one-third of the flash thrown by the others--that is, one-thirtieth of a second. This lamp is provided with all the necessary mechanism for keeping it in steady rotation at the increased speed, and for drawing current from its feed-cable.

Before the installation was placed in the lighthouse at Heligoland, it was submitted to searching tests at the Nuremberg works of the builders. These trials proved that with a current of only 26 ampères the average intensity was as high as 34,000,000 candle-power, with a maximum of nearly 40,000,000 candle-power; while with 34 ampères the average intensity rose to approximately 40,000,000, with a maximum of nearly 43,000,000 candle-power. Accordingly, the terms of the contract were fulfilled completely.

The searchlights throw their rays from a massive conical tower, the focal plane of which is 272 feet above sea-level. In average weather the rays are visible at a distance of twenty-three nautical miles, and under the most advantageous weather conditions visibility is limited only by the curvature of the earth, although on a clear night the light is seen from Büsun, which is about thirty-five miles away. The Heligoland electric light ranks as a remarkable development in the application of electricity to lighthouse illumination, but it never has been duplicated. The cost of maintenance--about £1,400, or $8,000, per annum--is an insuperable handicap.

On the other hand, the Hornum electric light, which is the most modern of its type in Germany, is more economical, although by no means so powerful. The tower is of cast-steel, and carries two electric lights; while about half a mile distant is a second tower, which throws a third electric light. In the main tower, on the ground floor, is installed the electric generating plant (in duplicate), together with all accessories, such as switchboards, etc. The floor above is devoted to housing 100 accumulators, which are charged during the day. This task can be completed by one generating set in about six hours. A single charge is sufficient to keep the three lights going for ten or eleven hours, and the lights are controlled by a simple throw-over switch. By this arrangement the cost of the maintenance of the light is reduced very appreciably, as only one keeper is on duty at a time, the station being equipped with two men, who have proved adequate for the purpose.

Above the accumulator-room is the storeroom and a general workshop, followed by a bedroom and above that the service-room. As only one keeper is on duty at a time, he is provided with ample devices whereby he can summon his comrade in times of emergency; the generating machinery is also controllable from this floor. From the service-room the lower light-room is entered. This is a secondary or back light in the range, the front light being in the tower half a mile away. Each of these two light-rooms is fitted with two 150 candle-power incandescent electric lights, but only one is burned in each set at a time: the second is a reserve. Should the light in action fail from any cause, although the keeper is warned of the occurrence, he does not have to stir a finger to bring the reserve light into service. The short-circuit produced by the accident to the light automatically revolves the table upon which the lamps are mounted, swings the reserve light into focus, and then sets it going.

Above the secondary light in the main tower is the principal beacon, comprising a brilliant rapidly-flashing light, the characteristic of which is groups of two flashes alternating with four flashes, the cycle being completed once in thirty seconds. The optical apparatus has been devised especially for the “differential arc-light,” as it is called, with a reflecting lens having a focal distance of 250 millimetres (10 inches), the lens itself being 1,180 millimetres (approximately 47 inches) in diameter. In front of the lens is placed a disperser, having a diameter of 1,200 millimetres (48 inches) whereby the ray of light is dispersed through an arc of 10½ degrees. Before the disperser is the means for producing the characteristic flash. This comprises a blind, or shutter, which is opened and closed by mechanism adjusted to requirements; while the rotating mechanism, instead of being weight-driven, is actuated by an electric motor.

The “differential arc,” which is utilized in this installation, is considered by German engineers to be the best system that has yet been devised for the exacting purposes of lighthouse engineering, and the description has arisen from the disposition of the carbons. While the positive carbon is held horizontally, the negative carbon is placed at an angle of 70 degrees thereto, and only the crater of the positive carbon is considered for the lighting effect, this being placed in the focus of the apparatus. The positive carbon is 3/5 inch, and the negative carbon 2/5 inch, in diameter, although both have a common length of 19 inches, which is sufficient for nine hours’ service. The beam emitted is of some 5,000,000 candle-power. This is one of the cheapest electric stations at present in operation, the annual running charges averaging less than £300, or $1,500.