CHAPTER IV.
THE INTERIOR OF A LIGHTHOUSE.
After having devoted so many pages to what we have called—perhaps somewhat fancifully—the _soul_ of the lighthouse, it becomes necessary to say a few words in reference to the _body_ which encases it.
In building up this body, no less ingenuity and science have been displayed than in perfecting and expanding the light which gives it life and value. Whether the lighthouse-tower is situated on some wave-washed rock surrounded by a hungry sea, or on the summit of a conspicuous headland, the highest skill is exercised upon its construction, and it becomes, in many instances, a monument of the most brilliant architectural genius. Not, indeed, that it exhibits those beautiful features of clustered columns and lofty arches, or that elaboration of picturesque ornament, which delight us in the lordly mansion and the ancient cathedral; but that an equal perfection of art is revealed in its massive simplicity and impregnable solidity, and in its admirable adaptation to the grand purposes for which it is intended.
Two primary conditions, it is obvious, must always govern the construction of a lighthouse: it must be raised to an elevation suitable for the full display of its warning radiance, and it must be built with a strength and solidity which will defy the assault of wind or wave.
So far as the first condition is concerned, the proper height of a lighthouse-tower is easily ascertained, when the distance is determined at which its rays should be visible. This distance will necessarily depend on the character of the neighbouring seas, and the nature of the reef, rock, or shallow from which the lighthouse is to warn the navigator; but, once determined, the elevation of the tower will easily be calculated by means of the known relations existing between the form of the earth, the effects of atmospheric refraction, and the proper height of an object which is to be seen from a given distance. The state of the atmosphere at any particular point is also an important point of consideration. It is quite possible that the lighthouse, when erected at what seems a suitable elevation, may be rendered useless by a prevalence at that elevation of dense mists and heavy fogs. In 1785, the Trinity Board commenced the erection of a lighthouse on the summit of St. Catherine’s Down, in the Isle of Wight, and from so lofty an altitude it might well be supposed that its radiance would illuminate the Channel for leagues around. But, unfortunately, the crest of St. Catherine’s is, for the greater part of the year, enveloped in cloud and mist, which effectually prevents the escape of a single ray of light; and, consequently, the Trinity Board were compelled to abandon their design. The shell of the building still crowns the bleak summit of the down, as a warning to future lighthouse-builders.
Still more recently, the lighthouse on the Needles Down (also in the Isle of Wight), which for years had pointed out the dangerous character of the western entrance to the Solent, has been abandoned on account of the mists so frequently obscuring its lustre; and a new lighthouse has been erected on the outermost of the celebrated Needle Rocks, in a position of far greater utility.
The question regarding the _interior_ accommodation of the tower must, in like manner, be answered by the nature of the locality where it is erected. Where it is easily accessible, and its stores can be replenished with ease at very short intervals, obviously the interior accommodation may be reduced within very narrow limits. But in exposed situations, as, for instance, on an isolated rock, whose communication with the mainland may be cut off for weeks at a time, room must be provided for ample supplies, and conveniences for the keepers must be arranged on a liberal scale. In the long and dreary nights of winter, where, in the northern parts of Great Britain, it is necessary to keep the light burning for about seventeen hours, not even for a moment is it left without the watchful care of at least one keeper; and thus, as he will require an interval of repose, its superintendence will occupy _two_ persons; but in open, exposed places like the Eddystone, the Bell Rock, the Wolf, and the Skerryvore, where it is frequently impossible to communicate with the mainland for three, four, and even six weeks, circumstances have rendered it desirable that there should not be fewer than _three_ men on duty. Hence, sleeping apartments have to be provided, as well as receptacles for sufficient supplies of water, food, fuel, and other matters.
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The second condition to which we have adverted is, that the building shall be capable of resisting the force of the wind and waves. The wind is baffled with comparative ease, but the sea is a far more formidable, and, moreover, is an ever-present foe. Even in the summer months the pressure of the waves is very considerable, averaging, perhaps, about 611 lbs. per square foot of surface exposed to it. In the winter, however, the average rises to 2086 lbs. per square foot; while, during stormy weather, the force has amounted to no less than 4335 lbs.[23] To oppose this immense pressure, not only must the masonry be of the solidest description, but such a form must be given to the building as will expose that masonry to the least possible stress. From various experiments it has been found that the most effective form is that of the cylinder; and with certain modifications, the cylindrical is now almost universally adopted in the erection of lighthouses. Scientifically speaking, however, it is not so much a cylinder as the union of frustra of different cones, with a curve osculating the outline of the successive frustra. To the youthful reader this may not be very intelligible, and we will, therefore, refer him to the form of the Eddystone as an illustration of what we mean. Smeaton himself relates that it was suggested to him by the trunk of an oak, but there seems reason to believe that this was an after-thought, intended for the benefit of the large class of minds which cannot appreciate scientific reasonings.
[23] These figures are the results of experiments made with an instrument invented by Mr. Thomas Stevenson, and called the Marine Dynamometer.
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Let us now pass into the interior of a lighthouse, and take notice of its general arrangements.
And, first, observe the massive door of bronze which opens to admit us into the lowermost story. Here are collected the stores of wood, cordage, oil, and water; and here too is placed the carpenter’s shop. On the next story we find the kitchen and the dining-room. Then we ascend to the sleeping-rooms of the three keepers; they are exquisitely neat and clean, but in other respects do not call for notice. On the highest story we enter that portion of the structure more particularly destined for the special service of the tower. It contains numerous vessels of oil, lenses, lamps, a thermometer, a barometer, and a chronometer. The spiral staircase by which we have hitherto ascended terminates at this point, and to reach the lantern we must climb a ladder before us. Entering the cupola, which enshrines the magic light, we are surprised by its exquisite propriety of arrangement. The form of the lantern is light and graceful; and to avoid the necessity of painting it, the framework is made of gun metal, and the dome of copper. A lantern for a light of the first order is twelve feet in diameter, and its glass frames are two feet high. The glazing is thick, and great care is exercised in fixing it that the plates may not be broken during high winds. Panes glazed in frames padded with cushions, and capable of being temporarily fixed in a few minutes, are always kept ready for use in Scotland. These are called _storm-panes_. The total cost of a lantern such as we have been describing is about £1260.
To secure a good and efficient light it is necessary that the lantern should be well ventilated. Otherwise its sides will be continually covered by the water of condensation produced by the contact of the ascending current of heated air, and the glass, thus obscured, impedes the passage of the rays and diminishes their power. To prevent such an evil an excellent system of mechanical ventilation was devised by the late Professor Faraday.
The ventilating pipe or chimney is a copper tube four inches in diameter, divided into three or four lengths; the lower end of each for about an inch and a half being opened out into a conical form, about five inches and a half in diameter at the lowest part. When the chimney is put together, the upper end of the bottom piece is inserted about half an inch into the cone of the next piece above, and fixed there by three ties or pins, so that the two pieces are firmly held together; but there is still plenty of airway or entrance into the chimney between them. The same arrangement holds good with each succeeding piece. When the ventilating chimney is fixed in its place, it is so adjusted that the lamp chimney enters about half an inch into the lower cone, and the top of the ventilating chimney into the cowl or head of the lantern.
With this arrangement (I use the Professor’s own words) it is found that the action of the ventilating flue is to carry up every portion of the products of combustion into the cowl; none passes by the cone apertures out of the flue into the air by the lantern, but a portion of the air passes from the lantern by these apertures into the flue, and so the lantern itself is in some degree ventilated.
The important use of these cone apertures is, that when a sudden gust or eddy of wind strikes into the cowl of the lantern, it should not have any effect in disturbing or altering the flame. It is found that the wind may blow suddenly in at the cowl, and the effect never reaches the lamp. The upper, or the second, or the third, or even the fourth portion of the ventilating flue might be entirely closed, yet without influencing the flame. The cone junctions in no way interfere with the tube in carrying up all the products of combustion; but if any downward current occurs, they dispose of the whole of it into the room without ever affecting the lamp. The ventilating flue is, in fact, a tube which, as regards the lamp, can carry everything up but conveys nothing _down_.
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The British lighthouses, as I have stated, are under the charge of either two or three keepers, whose duties are to cleanse and prepare the apparatus for nocturnal illumination, and to mount guard alternately after the light is exhibited. The rule is, that under no circumstance shall the keeper on duty leave the light-room until relieved by his comrade; and that no pretence may exist for disobeying this all-important regulation, the dwelling-houses are invariably built in immediate proximity to the light-tower, and means are provided for signaling directly from the light-room to the sleeping apartments below.
For greater security in all such exposed situations as the Eddystone or the Bell Rock, _four_ keepers are provided for one light-room. One of these is always ashore, on leave, with his family, and the other three are on guard in the lighthouse, so that, in the case of the illness of one light-keeper, an efficient establishment of two keepers for watching the light may remain.
The following interesting details we borrow verbatim from Mr. Alan Stevenson:[24]—
[24] Alan Stevenson, “On Lighthouses,” Weale’s Series, pp. 169, 170.
Each of the two (or three) light-keepers has a house for himself and family, both being under a common roof, but entering by separate doors. The principal keeper’s house consists of six rooms, two of which are at the disposal of the visiting officers of the Board, whose duty in inspecting the lighthouse or superintending repairs may call them to the station; and the assistant has four rooms, one of which is used as a barrack-room for the workmen who, under the direction of the foreman of the light-room works, execute the annual repairs of the apparatus.
The greatest care must be bestowed on securing the utmost cleanliness in every detail connected with a lighthouse, whose optical apparatus is peculiarly sensitive to the effect of dust. For this purpose covered ash-pits are provided at all the dwelling-houses, in order that the refuse of the fireplaces may not be carried on “the wings of the wind” to the light-room; and, for similar reasons, iron floors are used in the light-rooms instead of stone, which is often liable to abrasion, and all the stonework near the lantern is regularly painted in oil.
If, in all that belongs to a lighthouse, the greatest cleanliness is desirable, it is in a still higher degree necessary in every part of the light-room apparatus, without which the optical instruments and the machinery will neither last long nor work well. Every part of the apparatus, whether lenses or reflectors, should be carefully freed from dust before being either washed or burnished; and without such a precaution the cleansing process would only serve to scratch them.
For burnishing the reflectors, prepared _rouge_ (tritoxide of iron) of the finest description, which should be prepared in the state of an impalpable powder of a deep orange-red colour, is applied by means of soft chamois skins, as occasion may require; but the great art of keeping reflectors clean consists in the daily patient and skilful application of manual labour in rubbing the surface of the instrument with a perfectly dry, soft, and clean skin, without rouge. The form of the hollow paraboloid is such that some practice is necessary in order to acquire a free movement of the hand in rubbing reflectors; and its attainment forms one of the principal lessons in the course of the preliminary instruction to which candidates for the situation of a lighthouse-keeper are subjected. For cleansing the lenses and glass-mirrors spirit of wine is used. Having washed the surface of the instrument with a linen cloth steeped in spirit of wine, it is carefully dried with a soft and dry linen rubber, and finally rubbed with a fine chamois skin free from any dust, which would injure the polish of the glass, as well as from grease. It is sometimes necessary to use a little fine rouge with a chamois skin for restoring any deficiency of polish which may occur from time to time; but in a well-managed lighthouse this application will seldom, if ever, be required.
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Before we quit this subject, it may interest the reader to be informed that the glass of the lantern is frequently broken, not by wind and wave, but by the sea-birds which dash violently against it. In a single night at Cape de Bréhat nine panes were shattered from this cause. At the lighthouse of Bréhat a wild duck forced its way through two rows of mirrors and fell upon the lamp. A thousand of these birds were on one occasion caught by the crew of a British lightship, who made them into a gigantic pie. It is necessary to defend with trellis-work the lights most exposed to visits of this kind.
Fortunately, all sea-birds are not so dangerous. Some of them even render to the navigator a service like that which the goose of the capitol, according to Livy, once rendered to the Romans. At the South Stock lighthouse, near Holyhead, which is situated in the middle of an islet, tamed sea-birds are made use of as signals. The gulls perch on the lighthouse walls and utter loud cries, which wave off approaching seamen. This lighthouse possesses a bell and a cannon, but the natural signal has been esteemed so superior that the cannon has been removed to a distance from the rock, lest its discharge should alarm the birds. The young gulls roam about the island among the white rabbits, living in perfect harmony with them, and providing the keepers with society; a pleasanter society than that of the wind and waves which incessantly vent their fury on the solitary pharos.