During the past fifty years engineering science as applied to lighthouses has made remarkable advances. This has been due largely to the indefatigable perseverance and ceaseless labour of the chemist in regard to illumination. This wonder-worker has given us acetylene, has evolved means whereby oil-gas may be compressed to a pressure of several atmospheres with safety, and has discovered other gases obtainable by inexpensive and simple means. The engineer has not hesitated to profit from these developments, and has devised highly ingenious apparatuses whereby these illuminating mediums may be stored and used, so as to dispense with the human element almost entirely; in fact, in these instances the latter factor has been reduced to such a degree that it is only called upon to perform certain perfunctory operations, such as the recharging of the storage vessels at long intervals—three, six, or twelve months, according to circumstances.

This combination has provided the lighthouse engineer with a new, powerful, and efficient means of overcoming abnormal difficulties. Many a rock, reef, or stretch of uninhabited coastline has demanded indication, but has defied such protection from motives of cost, inaccessibility, or searching problems concerning the accommodation and relief of the keepers. As I have shown in the course of this volume, the erection of a first-class lighthouse is a costly undertaking, and the shipping interests, which in the case of Great Britain and a few other countries are called upon to pay the bill, naturally demur, unless the rock or other obstacle is situate in the centre of the marine thoroughfare, or the approach to a pitiless coast is extremely hazardous, when the erection of the tower becomes absolutely imperative. If one were to add up the costs of all the great lights scattered throughout the seven seas, it would be found that several millions sterling had been sunk in this humane effort, and yet, relatively speaking, but a small area of danger in the aggregate is safeguarded.

Then the human factor demands consideration. A colony of four or six men scarcely could be found willing to suffer isolation from the world at large and to be deprived of intercourse with their fellow-beings in the interests of shipping, say, through the Straits of Magellan, around Cape Horn, among the icy fastnesses of the Northern Labrador coast, or in Hudson Bay. Life in the lighthouses which guard the busy steamship lanes is monotonous and nerve-shattering enough, but to maroon men in such remote places as those mentioned above would be to promote a wholesale rush of inmates for the lunatic asylums.

This is where the chemist and the engineer in collaboration have triumphed. By their joint efforts it is now possible to supply the most inhospitable shore with a belt of lights equal in every respect to those mounting sentinel over the more densely populated reaches of coast in the civilized parts of the globe. The unattended lighthouse is a modern development born of necessity, which has proved highly serviceable, effective, and reliable. The passenger, as he lolls against the taffrail of the steamer ploughing her way carefully through the lane 375 miles long separating the mainland of South America from Tierra del Fuego, and watches the faithful star twinkling upon the top of a frowning cliff and urging the mariner to keep clear, may cherish a feeling of pity for the man who has to keep that beam shining. But his commiseration is misplaced. No human hands touch that beacon, perhaps, for six months or more at a time. It is a triumph of automatic operation. The same applies to the wicked shores of New Zealand, the uninviting northern stretches of the Gulf of Bothnia, the iron-bound coasts of Norway and Sweden, and many another unattractive mainland and island. All the great maritime nations possess several of these silent, faithful lights, which, although upon their introduction they were regarded with a certain amount of suspicion, owing to the urgent necessity of a light never failing in its duty for the guidance of the seafarer, yet have been proved by the convincing lesson of experience to be as reliable in every respect as the light which is tended by human hands.

So far as Great Britain is concerned, the unattended light has been brought to a high stage of efficiency and utility by the efforts of Messrs. David and Charles Stevenson, while in other parts of the world the apparatus and methods perfected by Mr. Gustaf DalÉn of Stockholm are used extensively.

The most interesting example of the Stevenson unattended lighthouse is provided in the English Channel, indicating the entrance to the strait which leads to the Guernsey capital of St. Peter Port. This was one of the first of its character to be erected, but the type is now being adopted widely owing to the success of this initial undertaking. The Channel Islands have achieved an unsavoury reputation in marine annals, as they form a graveyard of the Channel; they have claimed their victims, during recent years at any rate, mostly from the ranks of the heavy cross-Channel traffic.

The Russell Channel, leading to St. Peter Port from the north, is exceedingly dangerous, the sea being littered with granite rocks both submerged and exposed, of which the Grande Braye, Barsier, and Platte FougÈre, form the outer rampart. Readers of Victor Hugo may gather some realistic idea of the perilous nature of these waters by perusing “The Toilers of the Sea,” in which these rocks figure very prominently, particularly the Platte FougÈre. The menace of this corner of the channel is accentuated by the velocity of the tidal currents which swing and swirl round the reefs, together with the extreme range of the tides, which averages about 30 feet. Formerly, in thick weather, vessels found it almost impossible to pick up the Russell, and often a captain, by the rip and crash of metal being torn, to his dismay learned that he had swung too far to the westward.

The companies engaged in this traffic repeatedly petitioned the authorities to mark the entrance to the strait by some adequate means. A light was not required so keenly as a sound-signal, because in clear weather navigation was tolerably safe. The proposal was discussed time after time, but no solution appeared to be forthcoming. To erect a lighthouse on the outer fringe of the barrier would have entailed prodigious expenditure, which the island authorities could ill afford, even if such a scheme were practicable.

The question was taken up boldly by General Campbell during his occupation of the post of Governor-General of the Island of Guernsey, and he pressed forward the scheme vigorously in a resolute determination to bring about a diminution in the number of maritime disasters at this point. He approached Messrs. David and Charles Stevenson, who had considerable experience of similar conditions around the Scottish coasts, and they, after an elaborate survey of the site, recommended the erection of a light and fog-signal station upon the Platte FougÈre, which should be controlled from the land a mile distant. They agreed that the erection of a tower similar to those generally planted on sea-rocks would be a formidable undertaking and enormously expensive, owing to the conditions prevailing, but the station they suggested was quite practicable, and would serve the purposes equally well.

Instead of a massive, gracefully-curving tower, measuring some 40 feet in diameter at the base, these engineers suggested a building of irregular octagonal shape, measuring 14½ and 17 feet across the faces, 80 feet in height, and carried out in ferro-concrete. They advocated its erection upon the Platte FougÈre, because there the fog-signal would be brought into the most serviceable position for shipping. A narrow or thin building was advised, to offer the minimum of surface to the waves, which break very heavily on these ridges. The wisdom of this design has been revealed very convincingly since the tower has been in service. The seas fall on either side, divide and rush round the building, so that it does not experience the full brunt of their heavy, smashing blows. As the engineers pointed out, “It is better to avoid heavy sea pressures, where feasible, in preference to courting them.”

Still, the Platte FougÈre was not an ideal rock from the engineers’ point of view, although it is a solid knot of granite. Its head is visible only at low-water spring-tides, while it is difficult to approach, even in the smoothest weather, owing to the tides and currents. Much of the foundation work had to be carried out under water. The season was unavoidably limited, as the days when both the wind and the sea are calm in this part of the channel are very few and far between.

The tower is solid for a height of 46 feet above the rock, and the base is formed of Portland cement placed in iron moulds, with iron bars driven into the solid rock to anchor the concrete firmly. On the side to which the building is exposed to the heaviest seas, massive beams of rolled steel are driven into the rock, so as to impart additional strength to the part of the tower where the greatest strains are likely to be set up.

On the entrance level is a compartment containing an electric motor and air-compressor, while on the floor immediately above is a duplicate installation. The siren projects through the top of the tower, the trumpet being so turned as to throw the sounds in a horizontal direction over the water. On the top of the tower is a small automatic acetylene gas plant and light, such as the engineers have employed so successfully in their unattended Scottish light-stations, two air-receivers, and a water-tank. A new type of burner is used, and a clockwork mechanism is incorporated to extinguish the light at dawn and to ignite it at dusk, with a special arrangement to allow for the short summer nights and the long periods of darkness during the winter.

As mentioned above, the station is controlled electrically from a point on shore. In deciding the latter, it was necessary to discover the most favourable landing-place for the submarine cable in relation to its route, and Doyle Fort was selected as meeting all requirements in this direction. Here a two-floor dwelling has been erected for the keepers, together with an adjoining engine-house, which measures 32 feet in length by 20 feet wide. The tower being a mile distant, the designers had to meet the possibility of the machinery therein breaking down. Accordingly, at the shore station there is an auxiliary fog-siren and air-compressing plant, which is brought into use when the sea apparatus is deranged.

The machinery includes two oil-engines which drive three-phase alternators, and an air-compressor for working the land siren when required. One of the greatest difficulties arose in connection with the submarine cable which connects the land-station with the sea-tower. Owing to the broken, rocky nature of the sea-bed, the viciousness of the currents, and the heavy seas, the cable had to be of exceptional strength; indeed, it had to be made specially for the purpose. It is a double-sheathed, steel-armoured cable of the heaviest “rock” type, being 11 inches in circumference, and weighing 45 tons per nautical mile. As the current used is three-phase, there are three conductors, which weigh 1,100 pounds per mile, protected by a thick layer of gutta-percha averaging 450 pounds per mile. In the centre of the core are two other wires for switching and telephone purposes respectively. The laying of the cable was a peculiar and exacting task in itself; 6,504 feet had to be paid out. But by waiting for a very calm day and slack water this task was achieved without mishap. In the tower there is a simple switch operated by an electro-magnet, whereby the motor-driven air-compressors are thrown in and out of action. The two compressors are used alternately, so as to keep them in thorough working order; and as they have to be left sometimes for months without being examined, special attention has been devoted to their lubrication.

A visit to this lighthouse is a somewhat curious experience. Climbing the ladder and entering the building, one finds it apparently abandoned. Not a sound beyond the murmuring of the waves playing about the rocks below disturbs a silence which is uncannily tense. Suddenly there is an almost imperceptible click. The keeper at the light-station has moved his switch, and simultaneously that in the tower has closed. The electric motors instantly commence to revolve, with a low grunt at first, but rising quickly to a loud humming as they settle down to their stride, driving the air-compressors. Then comes the ear-splitting, deep-toned roar from the siren overhead, attended by the whirr of machinery in motion. The humming of the motors and the compressors dies down, and in a few seconds absolute stillness prevails once more. The sensation is decidedly eerie. It seems impossible that a silence so intense as to be felt should be interrupted by a click—the result of a slight movement by an unseen hand a mile away—which gives forth such a nerve-shattering din as to convey the idea that Bedlam had been let loose. At the land-station the experience is similarly weird. The keeper moves his switch which brings the tower machinery into action. Presently there is the sharp tinkle of an electric bell. This notifies the keeper that the blast on the tower has been given, but conclusive evidence of this fact does not arrive until five seconds later, when the baying of the siren comes rolling over the water.

A complete check is kept upon the isolated station out at sea. If the electric bell does not ring out at the appointed period, to notify the keeper that the siren has emitted its warning note, he knows that something is amiss. The land-station is brought into service without delay, the intimation to the mariner to stand clear being thrown from Doyle Fort once every ninety seconds. The men on shore take it in turns to mount watch for fog both day and night, and their vigil is checked. There is an electric alarm, which maintains silence only so long as the man on duty fulfils his appointed task and records this fact upon his mechanical register at scheduled intervals. Should he fail to perform this function, there is a frenzied clanging by the alarm-bell, which summons the second keeper to duty.

Apparently, the weakest point in the installation is the submarine cable, but the engineers entertain no apprehensions on this score. It is too stoutly made and too heavily armoured to rupture very readily. Experience has proved its efficiency and reliability, while a long life is anticipated for it. The Platte FougÈre unattended lighthouse has opened up new possibilities for protecting wild coasts. It has proved conclusively that there is no difficulty in maintaining such a station and controlling it from a distance so long as automatic apparatus which has proved its worth is employed. This practical application should serve to solve many peculiar problems. No longer can the bogie of expense be put forward as an argument against safeguarding a notoriously evil length of shoreline or isolated rock, even if the latter is exposed to the heaviest seas known. The Guernsey installation was completed for £8,500, or $42,500, and is as serviceable as the ordinary type of tower, which in this instance would have cost at least £60,000, or $300,000, to build and equip. From the maintenance point of view it is equally convincing and economical, inasmuch as only two keepers are required in the place of the four who otherwise would have been necessary.

The system which has been devised by Mr. Gustaf DalÉn of Stockholm, and which is exploited by the Gas Accumulator Company of the Swedish capital, operates with dissolved acetylene. The first light in Scandinavian waters to be brought into action upon the “Aga” principle, as it is called, was installed in the Gasfeten tower, an exceedingly isolated beacon which offered every means of testing it thoroughly. The idea follows the broad lines of that adopted in connection with lightships, and, the Gasfeten experiments proving completely successful, it has been adopted extensively since, not only by the Swedish authorities for the lighting of lonely waters in the Baltic Sea and Gulf of Bothnia, but by various other Powers. The Straits of Magellan are protected in this way, and when one recalls the sparse population which dwells upon the banks of this short-cut between the Atlantic and Pacific Oceans, and bears in mind the fact that the lights have to be left to their own automatic action for some months on end, then one may realize the perfection and reliability of the invention. The failure of a light in such treacherous waters would be notified speedily to the authorities responsible for the illumination of this sea-lane, but no such complaints appear to have been received from passing vessels. These lonely lights for the most part are of a very simple character, a result due to local conditions. As a rule they are planted on lofty eminences—not at too high an elevation, as thereby they might be rendered useless by headland fogs—at a height varying between 150 and 250 feet. The base of the tower forms a space for the accommodation of the gas-accumulators, wherein the illuminating medium is stored under pressure, surmounted by the lantern which carries the requisite optical apparatus, and the flasher whereby the characteristic visual warning is given.

Although adoption of the flasher enabled the consumption of gas to be reduced very appreciably, there was one noticeable drawback: the light had to burn both night and day, unless clockwork mechanism were introduced to extinguish the light at sunrise and to ignite it at twilight. Some authorities, however, do not place trust in clockwork mechanism. Certainly it is liable to fail at a critical moment, and in the case of an isolated light, several hundred miles from the nearest base, this would be a serious calamity, intimation of the fact not being available until several weeks after the disability had been observed.

In order to overcome the fallibility of clockwork, and to insure a still further marked decrease in the consumption of gas, Mr. Gustaf DalÉn devoted his energies to the perfection of a device which should achieve the self-same end, but be operated by Nature herself. His efforts were crowned with complete success by the invention of the “light-valve,” but which has become more widely known as the “sun-valve.”

This device is based upon a well-known principle. If two objects, fashioned from the same metal, and identical in every respect except that one is made light-absorbing and the other light-reflecting, are exposed to daylight, while the former will expand, the latter will remain unaffected. This result is due to the fact that the one which absorbs light transforms it into energy. The acting part of the “sun-valve” therefore is a light-absorber. It consists of a central rod, the surface of which is coated with lampblack, so that its light-absorbing qualities are enhanced as much as possible. The lower part of this rod is connected to a small lever, which opens and shuts an orifice through which the gas passes to the flasher in the lantern above. Around this central black copper rod are three other copper rods, disposed equidistantly. They resemble the former in every respect except that they have no light-absorbing qualities, but they are given polished gold surfaces, so that their light-reflecting properties are raised to the maximum.

This sun-valve is exposed. At the break of dawn, under the gathering intensity of daylight, the central black rod absorbs the luminosity, the amount of which is increased by the light thrown from the gold-burnished outer rods, and, converting it into energy, expands longitudinally. In so doing it forces the lever at the base downwards, closing the opening through which the gas flows to the flasher. In a short while, when the day has broken fairly and there is no further need for the beacon’s services, the gas-feed is cut off entirely, only the pilot burner remaining alight, the gas-supply to this not being affected by the sun-valve. In order to bring the greatest possible pressure upon the lever, the blackened rod is so arranged that it can expand only in one direction—namely, downwards.

Upon the approach of evening, owing to the daylight becoming weaker, the blackened rod contracts, and, the pressure upon the lever being released, the gas commences to flow once more to the burner. It is a small stream at first, but as the darkness gathers, and the shrinking continues, the valve opens wider and wider, until at last, when night has settled down and the copper central rod has fully contracted, the gas-valve is opened to its fullest extent, permitting the greatest pressure of gas to flow to the burner, so that the beacon throws its most brilliant light. This automatic action continues infallibly every dawn and dusk, and is the simplest and at the same time most reliable means of economizing gas during the day that has yet been devised.

There is another feature of this system which must not be overlooked. Suppose, for some reason or other, that the sea becomes shrouded in suffused light, such as might arise from the obscuring of the sun by an overhanging bank of fog or smoke, the beacon comes automatically into service, as the cutting off of the daylight must bring about a contraction of the blackened copper rod controlling the valve.

The central rod can be adjusted to any degree of sensitiveness, by means of a screw, while protection of the vital parts is insured by enclosure within a heavy glass cylinder. The first apparatus of this character was tested by the Swedish authorities in 1907, and proved so successful that it is now in service at all the exposed unattended lighthouses in Swedish and Finnish waters; while it has been adopted, also, very extensively by the United States, more particularly for the lighting of the lonely stretches of the Alaskan coastline and of the Panama Canal.

Of course, the saving of gas which is rendered possible by the use of the sun-valve varies according to the season of the year. During the winter, when the nights are long, the saving may not be very marked, but in the summer, when darkness does not last more than four or five hours, the economy is very noticeable. According to the experience of the Swedish authorities, the average saving of gas during the year varies from 35 to 40 per cent., as compared with similar lights not fitted with this device.

But there is another factor which is influenced to a very appreciable degree by the utilization of the sun-valve. By cutting off the light when it is not required, the capacity of—i.e., the duration of service upon—one charge is lengthened, and this in the case of an isolated light is a very important consideration. In fact, with the “Aga” system wherein the sun-valve is combined with the flasher, it is possible for the light to work a round twelve months without the least control or necessity for intermediate inspection, and at as low an annual charge as £2 15s., or about $14.

One of the latest unattended installations which have been carried out upon these lines is the Lagerholmen lighthouse, marking a dangerous rock in the Baltic Sea. It is a cylindrical tower, with the focal plane 56 feet 4 inches above sea-level, and the flashing light, with sun-valve control, has a range of eighteen miles. The geographical range, however, is only thirteen miles, owing to the comparatively low height of the tower.

An interesting and ingenious automatic unattended light has also been established in an isolated part of the Bristol Channel. It was designed by Sir Thomas Matthews, the engineer to the Brethren of Trinity House. This is purely and simply a clockwork-controlled apparatus in which extreme care has been taken to eliminate the disadvantages incidental to such mechanism. This type of light was designed to fulfil three conditions—to give a flashing light; to light up and go out at the proper times; and to require attention only at long intervals. Acetylene is the illuminant used, the gas being stored in a reservoir under high pressure. The gas as it emerges from the supply cylinder is expanded, so that the pressure at the burner does not exceed 2 pounds per square inch.

The outstanding feature of this apparatus is that the clockwork control cutting off and turning on the gas does not require to be wound by hand, but is actuated by the mechanism which revolves the lenses, through a simple set of gearing. The gas as it issues from the reservoir passes into one of two cylinders. Each of these is provided with an inlet and an exhaust valve, while the upper end is closed with a lid of leather, covering the top like the vellum of a drum. To each leather cover is attached a circular piece of metal, smaller than the leather diaphragm, and from this in turn extends a vertical rod, the upper end of which is connected to one end of a centrally pivoted rocking arm. When the gas enters one cylinder, naturally in expanding it forces the leather lid upwards, and with it the vertical rod. This elevates the corresponding end of the rocking arm, and simultaneously drives down the rod attached to the opposite end of the beam, which in turn drives down the leather lid of the second cylinder, and forces out any gas that may be therein. The apparatus consequently is something like a double pump, owing to the rocking arm having a seesaw motion. This reciprocating action serves to wind up the clock, and also to revolve the lenses through spurs and pinions. The mechanism, however, is controlled completely by the clock whereby the light is started, inasmuch as without this the apparatus cannot be set in motion. There are two dials, one of which is divided into twenty-four divisions, corresponding to the hours of the day, and the other into twelve divisions, representing the twelve months of the year. The clocks work together, and the time of lighting up is advanced or retarded, according to the time of the year, through the clock train wheels.

The apparatus is very compact, highly ingenious, and has proved efficient in service. Although this is the first application of the idea for rotating the lenses by the gas which feeds the burners, so far as England is concerned, it has been employed under similar circumstances in Germany with conspicuous success, in combination with the Pintsch oil-gas apparatuses, but it lacks the simplicity and reliability of the sun-valve.

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 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.

The maintenance charges are guided by the local market values of materials and labour, the item of repairs and renewals being practically negligible. So far as oil consumption per month is concerned, this fluctuates according to the type of lamp used, ranging from 1¹/₅ pints per twenty-four hours, or 4·8 gallons per month, in the case of a 1¹/₈-inch single-wick burner, to 2¼ pints per twenty-four hours, or 8¾ gallons of oil per month, in the case of the latest 1⁵/₈-inch duplex-wick burner. American petroleum-oil, of a specific gravity of about 0·795, gives the best results and the brightest and clearest flame. Russian and other heavier oils generally used in lighthouses are unsuitable. In view of the world-wide operations of the Standard Oil Company, however, no difficulty is experienced in procuring adequate supplies of this oil anywhere between the two Poles.

The oil used in the float cylinder, as mentioned previously, is quite distinct from the burning oil, and is used only to support the float to which the wick is attached. As the oil escapes through the drip-valve, it may be allowed to run to waste, or, what is far preferable, it may be caught, filtered, and used again for this purpose, to bring about a reduction in the cost of upkeep. The float cylinder of a thirty-one-day light, irrespective of the number of wicks, requires the same quantity of oil for the float cylinder—9½ gallons.

The advantages of the unattended, automatic light have been appreciated by the various maritime Powers, and their application is being developed rapidly. They are inexpensive in first cost, and their maintenance charges are very low. In Sweden a second-order light, consuming 6 cubic feet of acetylene gas per hour, throwing a fixed white light of 4,000 candle-power, and visible for seventeen miles in clear weather, costs about £15, or $75, per annum; while the smaller lights, with a 300-millimetre lens and a 12-inch burner emitting 360 candle-power, may be run for £2, or $10, per annum, the low cost in this instance being attributable to use of the DalÉn flasher and sun-valve.

The cost of the acetylene gas averages ¾d., or 1½ cents, per cubic foot, a result attributable to the fact that Scandinavia is the world’s largest producer of carbide of calcium.

The Wigham petroleum system has proved similarly economical and reliable, and has been installed in some of the wildest corners of the globe. The Congested Districts Board for Ireland have established a number of these beacons on the rugged west coast to assist the fishermen in making their harbours at night. Many are placed in very exposed positions on headlands, where they are frequently swept by the full force of the Atlantic gales. The Austrian Government has adopted the principle for lighting the dangerous coasts of the Adriatic near Trieste, while the shoreline of Jamaica is safeguarded by more than sixteen lights of this type. Many of these lights suffered severely from the effects of the earthquake which overwhelmed the island a few years ago, but others withstood all the shocks successfully. In this instance, had expensive and massive lighthouses of the usual type been erected, the loss would have been considerable, in view of the severity of this seismic disturbance and the widespread destruction which was wrought. These lights play a very prominent part in the guarding of the southern ocean, the Australian shores being protected by over sixty such beacons, many of which are established in very exposed and isolated positions off the mainland.

While the day is still far distant when expensive graceful towers, carrying immensely powerful lights, will be no longer constructed, the perfection and utility of the unattended light, in one or other of its many forms, are assisting tangibly in the solution of the problem of lighting busy shorelines adequately and inexpensively. Structures costing tens of thousands sterling in future will be restricted to important places, especially in connection with sea-rocks, such as landfalls, or to those some distance from the land, where a fog-signal station must be maintained, unless the example of the Platte FougÈre land-controlled station becomes adopted.