Lighthouse, a structure from the top of which a light is shown at night as a direction or warning to mariners. Lighthouses are necessarily situated on headlands, isolated rocks or sands, and pierheads; and from the benevolence of their design, and in many instances from the boldness of their construction, they have always been objects of interest independently of their use to mariners. We propose to treat the subject under the following divisions: 1, materials and mode of construction; 2, method of illumination; 3, auxiliary safeguards to navigation; 4, history and statistics. 1. Materials and Mode of Construction. The materials used in the construction of lighthouses are wood, stone, brick, cast iron, and wrought iron. Stone, brick, and iron are the most important, and are used exclusively in all large lighthouses. The most noted lighthouses in the world are built of stone; and in northern climates, where the first cost is not the great consideration, stone should be exclusively used. The form of all stone lighthouses approaches more or less the frustum of a cone or pyramid. They are sometimes built to include the keepers' apartments, but more usually they merely contain the staircase and cleaning and watch rooms, with a receptacle for the oil butts.
In all cases where large lighthouses are built of this material, the masonry should be of the best cut stone with hydraulic cement mortar. The first cost should never be so limited that this principle cannot be fully carried out. The same principle applies to brick lighthouses, which should be built of the best and hardest bricks, laid in hydraulic cement mortar. The interior walls of all lighthouses should be as separate as possible from the outer walls, in order that there may be a free circulation of air between the walls. The dryness of the inner wall is insured by this arrangement, without which all large masses of masonry like large lighthouses must be constantly damp. The inner wall must of course be firmly tied to the outer shell by masonry or iron ties. Cast-iron lighthouses were first erected by Mr. Alexander Gordon, an English civil engineer. Two were constructed in England, and were erected on the islands of Bermuda and Jamaica. From the fact that every part of the structure can be completed at the workshop, cast-iron lighthouses answer admirably for positions at points remote from large centres of manufacture, and are gradually coming into use.
Several lighthouses of this kind have been erected at various places on the coasts of the United States. They require a lining of brick, the weight of which prevents oscillation or swaying, while its low conducting power of heat hinders the deposition of moisture on the well room of the stairs, which would otherwise be occasioned by the difference of temperature between the inside and outside of the tower. To further" this latter object space is also left for a current of air to flow between the iron and brick. Another kind of iron lighthouse is the wrought-iron pile lighthouse. The lower ends of the iron piles are fitted with large cast-iron screws where the foundation is soft, and the piles are screwed to a firm bearing, or where the foundation is rock these ends are sharpened, and the piles are driven into the rock or hard ground by an ordinary pile driver, until they come to a firm bearing upon cast-iron disks which bear upon shoulders forged on the piles. The number of piles depends upon the plan of the structure, which may be square, hexagonal, or octagonal. The foundation having been placed, the structure, which is of wood or boiler iron, firmly braced to the piles, and connected with them by iron castings, is easily built upon it.
This kind of lighthouse was first built in England; the screw pile was patented about 1836 by Mitchell, and is called Mitchell's screw pile. It was introduced into the United States about 1845, and has since been used in the construction of many important lighthouses on the coast. Experience has shown that iron-pile lighthouses are not suitable for foundations in water in climates where much ice is formed. The ice, moving in large fields, bends and sometimes breaks the piles, and, by forming upon the piles themselves, makes the bulk of the structure so large that the effect of the waves upon it is very much increased. On this account it is not likely that iron-pile structures will be much used north of Chesapeake bay; but on the southern coasts they have been found particularly adapted to the necessities of the service, and about 70 of this class of structures, resting upon screw piles and iron disks, now exist in the United States. Their annual cost for repairs is very small, a yearly coat of paint being all that is needed to keep the exterior in good order. They are particularly suited for bays and sounds in the southern waters, where light vessels have been in use until the present time.
As these vessels become in need of repairs, they are withdrawn, and a screw-pile lighthouse is built upon the site, at a cost not much exceeding that of the repair of the vessel, and with an annual expense of maintenance less than one half of that of the vessel. - Lighthouse towers are generally surmounted by parapet walls, which vary in height from 3 to 7 ft. according to the order of the light. Upon the parapet wall is placed the lantern in which the illuminating apparatus is contained. The lantern is a glazed framework made of brass or iron, and varies in dimensions from 6 ft. in diameter and 4 ft. in height to 12 ft. in diameter and 9 ft. in height. It is a regular polygon, and can be made of any number of sides, depending upon the various circumstances to be considered. It is surmounted by a dome constructed of copper or iron, which is generally lined with some other metal, leaving an air space between the two metals, to prevent condensation of moisture. A ventilator is placed upon the top, from which the heated air escapes, and registers are inserted near the bottom of the lantern to enable the keeper to regulate the supply of fresh air at will.
Upon the convenience and proper construction of the lantern the efficiency of the lighthouse in a great measure depends.
The materials which have been used for the illumination of lighthousesare: 1, wood and coal; 2, candles; 3, oil; 4, gas; and 5, the electric current acting upon carbon points. Wood and coal were the first fuels used for lights. They were first burned as beacon fires on headlands, and afterward, as the necessity of increased elevation was felt, the fire was placed at the top of a tower. It is not known that any other method of illumination for lighthouses was used until about 1760, when Smeaton commenced the use of wax candles in the Eddystone lighthouse. Another lighthouse built by him on Spurn point about 1774 was arranged for illumination by coal, which fact shows that the use of wax candles had not become general at that date. Tallow candles were afterward used at the Eddystone. Some of the English and Scotch lights consumed coal as late as 1816, and several on the coasts of Sweden and Norway were illuminated with this material as late as 1846. The vast improvement made in lamps by the use of the Argand burner and glass chimney made a complete revolution in,the lighthouse systems of the world. The parabolic reflector with this burner was introduced into lighthouses gradually from 1785, when the first apparatus of this kind was erected in the Cordouan lighthouse.
In the United States the first lighthouses were lighted with tallow candles and solid-wicked lamps, suspended from the domes of the lanterns by iron chains. The lamps were in shape and in principle like the old-fashioned links. The Argand burners and reflectors were adopted in 1812, and were used till 1852, when the general introduction of the lens system commenced. Since the adoption of Argand lamps in lighthouses, oil has been used as the combustible. In Europe the vegetable oils (olive and rape-seed or colza) have been generally used. Great Britain however uses sperm oil as well as colza, though the latter bids fair to supersede it. Various other oils, animal and vegetable, have been tried with more or less success, but hitherto none but the sperm and lard among the animal oils, and the colza among the vegetable, have come up to the requirements of lighthouse illumination. In the United States lard oil is the fluid now generally used. Its cost is about one third that of sperm oil, and although its freezing point is some degrees higher, this objection is not material in climates the winter temperature of which is lower than the freezing points of both oils.
Its capillarity is greater than that of sperm oil, so that a higher wick can be used with it, without danger of smoke. - Attempts have been made to use gas in lighthouses. Difficulties have been found in getting the proper shape of flame for deviation by the illuminating apparatus; and the uncertainty of the supply where the gas is made at the lighthouse is another objection, and one so serious that a full supply of oil has had to be kept at the station for fear of accidents to the gas apparatus. In a few cases gas has been introduced into lighthouses near towns supplied with it. These, however, have been small lighthouses, and the examples are from the nature of the case rare, and cannot be extended beyond harbor lights. In one case in the United States a lighthouse is lighted with natural gas. In the present state of the gas manufacture it seems impossible to make a burner that will give the proper size and shape of flame for the large orders of lights. No metal but a very refractory one can bear the intense heat developed by four cylindrical concentric flames, the largest of which is 3 1/2 in. in diameter; and the expense of making burners of such a metal would be very great. As an economical question it is doubtful whether gas should be substituted for oil.
The first cost of the gas apparatus for a large lighthouse is heavy, and the annual expense of repairs is also large. It is probable that the efficiency or brilliancy of the light would not be materially increased by the change from oil to gas, as the lights fitted with Fresnel apparatus now show as far as the curvature of the earth will permit. - Experiments have been made in the United States on the electric light by Prof. Henry, chairman of the lighthouse board. He came to the conclusion that the slight gain in its power of penetrating fogs does not compensate for the increased cost of apparatus, difficulty of attendance, and liability to derangement. In a lecture delivered March 9, 1860, before the royal institution, Prof. Faraday spoke of the light produced by electricity as being especially adapted for lighthouses on account of its intensity, while it occupied at its source no more space than a common candle. The voltaic battery, however, presented difficulties which rendered its use for this purpose impracticable, but from which the magneto-electric apparatus was found to be free.
A large apparatus of this character, worked by a two-horse steam engine, had been employed for six months at the South Foreland lighthouse, which produced such an intensity of light that it was often seen from the opposite coast of France. Prof. Faraday anticipated that, if the expense of this mode of illumination did not prove too serious, it would be adopted in many situations where intense light is required. - Experiments have been made upon kerosene with reference to its use in lighthouses, but it is not feasible to make the flame of this oil of the proper size and shape for deviation by the large lenses, in the present state of knowledge on the subject. The difficulty appears to be that the immense heat of so large a flame sets free a great amount of carbon, which passes off unconsumed as smoke, and covers the apparatus and glass of the lantern with a thick coating of black. Until means can be devised for the consumption of this excess of carbon, kerosene cannot be used. Experiments lately made in the United States have convinced the lighthouse board that petroleum is too dangerous a fluid to be used for lighthouse purposes.
The danger consists not merely in burning it in a proper lamp, but in its transportation in large quantities, in drawing it from the butts, and in filling the lamp reservoirs. In Europe, however, petroleum is coming into general use, and France has ordered a change to mineral oil in all of its lighthouses. - The illuminating apparatus is either catoptric by reflectors, or catadioptric by lenses. The latter method of illumination has been fully described in the article Fresnel. In the catoptric method, which was mostly used until within the last 30 years, the light from each lamp is so deviated by a reflector that it emerges from the lantern, a beam, or nearly a beam, parallel to the horizon. The earliest known instance of a reflector being used for this purpose was in the Cordouan lighthouse, in the bay of Biscay. With the introduction of the Argand burner its use became more common. The reflectors at first were plaster moulds made of the proper form, upon the interior surface of which were fastened facets of plane silvered glass. They came into general use in Europe in the early part of the present century. The best form of reflector is the paraboloid of revolution with its axis horizontal.
The reflector is made of copper, and its inner surface is covered with silver and is highly polished. The flame of the lamp has its centre in the focus of the reflector, and the rays emerge from the surface of the reflector nearly parallel. They are not entirely parallel, because the surface is necessarily imperfect, and the source of light cannot be a mathematical point. The small divergence, instead of being a defect, is in reality a benefit, for without it the beam would always have a diameter equal to that of the edge of the reflector, and would be of little practical value. In fixed lights, the reflectors are fastened to circular iron frames, and are placed in horizontal tiers in the lantern. There is a lamp for each reflector, and it follows that the greater the number of lamps the more uniformly the light is distributed around the horizon. The reflectors vary in their sizes. The double ordinate at the lips is about 11 in. in the smallest and 21 in. in the largest size. Some have been made larger, but they have never been in general use. In a revolving reflector light, the reflectors are generally arranged so that the axes of all of them on one face are parallel, and there are two, three, or four faces, the number depending on the desired interval between the flashes.
The frame upon which they are placed is made to revolve by a clockwork arrangement moved by a weight. It is evident that the flash produced by one of the faces will be brighter than the light of a fixed reflector light, because the eye will receive at once rays from several reflectors, while in the case of a fixed light it only receives them from one. This is the reason why revolving lights are always brighter than fixed lights. The lamps used with reflectors are what are commonly called fountain lamps. They are fitted with Argand burners, about three fourths of an inch in diameter. Figs. 1, 2, and 3 represent a vertical central section, a side elevation, and a rear elevation of a lamp and reflector: a a a a is the reflector; b, the burner; b', the glass chimney; c, the fountain, holding about two thirds of a quart; d d d d, a frame to which the lamp is fastened; e and f, guide rods upon which the frame is movable vertically for raising and lowering the lamp; g, a handle, by turning which the lamp is fastened in position; h, a copper tube for ventilation, which is inserted in an elliptical aperture in the upper part of the reflector, corresponding to one in the lower part through which the burner can be moved out and in; i, a portion of the frame to which the lamps and reflectors are attached; k k, brass knobs soldered to the outside of the reflector; l, an iron band upon which the knobs rest, thus holding the reflector in place.
Fig. 3 shows the frame d d on which the lamp is mounted, the guides e e through which the rods slide, the guide rod f, and handle g; l' is the dripping cup. The communication between fountain and burner is opened by giving the fountain one quarter turn, which opens a slide valve, covering the flow-hole. This flow-hole is about three eighths of an inch below the top of the burner, measured vertically. Figs. 4, 5, and 6 give an elevation of the lamps and reflectors in a revolving apparatus, a plan of the same apparatus, and a plan of the lamps and reflectors in a fixed light: n n n is the frame; o o o, the reflectors; p p p, the lamp fountains; q, the central shaft; r r r, the tubes which lead off the smoke; s s s, the braces supporting the shaft; t t, supports of the shaft; u u, a pan for catching drops from the roof; I, a bracket supporting the foot of the shaft; m m, bevelled wheels conducting the motion from the apparatus which moves the system. The introduction of the Fresnel or dioptric method of illumination of lighthouses has superseded the reflector system, so that reflectors are now only used as range lights, or on light vessels, or in lighthouses built with too little money to permit the purchase of a lens. Fig. 7 shows a plan and elevation of a Fresnel lens of a small order.
It consists of thirteen rings of glass of various diameters arranged vertically one above the other. The five middle rings are 11 13/16 in. in internal diameter, and by two refractions throw the rays which they receive from the flame F to the horizon. The five upper and three lower rings throw their rays to the horizon by two refractions and one total reflection. The dotted lines show the courses of the rays after they leave the lamp. F is the flame; r r, cylindrical refractors; x x, catadioptric rings acting by refraction and reflection'. The external lines r' r' represent a system of vertical prisms which revolve around the apparatus described above, and by deviating the rays as represented in the plan, so that they leave the prisms parallel to each other, cause the variation in the light described in the lists as a "fixed light varied by flashes." The first cost of a lens of the first order is four times as great as that of 20 reflectors, which is the greatest number placed in a lighthouse.
These consist of light vessels, beacons, fog signals, and buoys. Light vessels are vessels moored to point out dangers or show the entrances of channels, turning points, etc, by exhibiting a light at night. They are strong, and built for riding easily at anchor, and are well manned, to provide against accidents to which their exposed positions render them peculiarly liable. The lighting apparatus is contained in a lantern which at night is hoisted to the masthead. It consists of lamps and reflectors like those described above for lighthouses, except that they are smaller. The lamps are hung on gimbals, so that their positions may be affected as little as possible by the motion of the vessel. During the past ten years Fresnel lenses have been successfully applied to light vessels. Some of the light vessels of the United States are in positions exposed to the full force of the Atlantic, and one moored off the Nantucket New South shoal is 22 m. from the nearest land. On account of the great expense of maintaining light vessels, and the little dependence that can be placed on them as signals when they are the most needed, they are only placed near dangers which it is impossible to point out by lighthouses. - A beacon is a structure of stone, iron, or wood, placed upon the shore or upon a rock or shoal in the water to designate a danger.
Beacons are built at points where lighthouses cannot be built, or which are not of sufficient importance to justify the constant expense of keeping up lighthouses or light vessels, but which nevertheless require to be pointed out. - A fog signal is an aid to navigation placed on board a light vessel or near a lighthouse to give warning to vessels in time of foggy or thick weather. They are of the greatest importance, hardly if at all inferior to lighthouses. In fogs no light can be seen far enough to be of use, and a signal by sound is the only one that can give warning of the presence of danger. Bells are the most common signals, and when placed on light vessels they are very efficient. When, however, they are placed near lighthouses, as the shore is generally between the bell and the vessel to be warned, the roar of the surf is likely to drown the noise of the bell; so that in such cases they are inefficient, and can only be heard when the vessel is close to the lighthouse, often too close to avoid the danger. Whistles, horns, and sirens are also used as fog signals, and are more efficient than bells, because their sounds are heard further. They are sounded by steam or air engines, and their positions are indicated by the lengths of and intervals between the blasts.
The siren is actuated by steam or compressed air, and is constructed as follows: There is a hollow flat right cylinder with circular base made of strong metal. In the centre of one of the bases is a hole to which is attached a metal tube connecting the cylinder with the boiler, or reservoir of compressed air. The other base contains eight holes symmetrically arranged about its centre. A plate of metal concentric with this base, and close to it, having in it corresponding holes, is made to revolve with any required velocity. In front of this plate is a large horn, which is in accord with the tone or note made by the siren. Then, when steam or compressed air is admitted into the flat cylinder, the revolution of the metal plate opens and closes the eight holes in the base with great rapidity, producing an intense sound of great volume, which is transmitted in the required direction by the horn. Sounds from the siren have been heard at a distance of 25 m. This instrument has been experimented upon with great success by Prof. J. Henry and Gen. J. C. Duane of the lighthouse board, and forms the best fog signal in the world. The intervals between the sounds can be so arranged as to make each instrument indicative of the station where it is placed.
The objection to it is its great expense, as it involves a steam engine and the persons necessary to attend it, with fuel, fresh water, etc. This expense, however, is common to the siren and the ordinary horn with the reed attachment. Constant efforts are made in all civilized countries to increase the efficiency of these signals. - Buoys are anchored in the water to mark rocks, shoals, and other dangers. They are of various kinds, such as nun, can, and spar buoys, etc. A nun buoy is in shape like two equal cones brought together at their bases; it is made like a barrel with staves and iron hoops, or, as is often the case in the United States, it is made of boiler iron. A can buoy is nearly conical in shape, and is moored at its vertex. A spar buoy is a spar anchored at one end. Buoys are painted of different colors to indicate upon which side they must be passed. The colors are fixed by law of congress in the United States. Thus a red buoy must be left on the starboard hand by a vessel entering a harbor from sea, and a black buoy must be left on the port hand. A buoy with red and black horizontal stripes may be left on either hand. The side of a channel upon which a buoy is placed is sometimes indicated by the kind of buoy.
Thus nun buoys may be placed on the starboard side of a channel, and can buoys on the port side.
Little is known of the early history of lighthouses, but sea lights are mentioned by Homer in the Odyssey, and they are also referred to in the Greek poem of Hero and Leander. These must have been merely fires kindled upon headlands. The most noted lighthouse in the world for size and antiquity was the Pharos of Alexandria. This building was the frustum of a square pyramid surrounded by a large base, the precise dimensions of which are not known. It was commenced by the first Ptolemy, and was finished about 280 B. 0. The style and workmanship are represented to have been superb, and the material was a white stone. The height was about 400 ft.; and it is stated by Josephus that the light, which was always kept burning on its top at night, was visible about 41 m. It was probably destroyed by an earthquake, but the date of its destruction is not known. Enough is known, however, to make it certain that this tower existed for 1,600 years. The island upon which it is situated was named Pharos, and the structure took its name from its site.
To this day the French word for lighthouse is phare, and the Italian and Spanish faro. - One of the most remarkable modern lighthouses is the tower of Cor-douan, which was commenced in 1584 and finished in 1010 by Louis de Foix, the construction having occupied 26 years. It is situated on a ledge of rocks in the mouth of the Garonne or Gironde, in the bay of Biscay. The ledge is about 3,000 ft. long and 1,500 ft. broad, and is bare at low water. It is surrounded by detached rocks, upon which the sea breaks with terrific violence. There is but one place of access, which is a passage 300 ft. wide where there are no rocks, and which leads to within 600 ft. of the tower. The foundation is the frustum of a circular cone whose lower base is 135 ft. in diameter, and is built solid of cut stone to a height of 16 ft., a space for a cellar and water cistern 20 ft. square and 8 ft. deep having been left in the centre. The upper base of the frustum is 125 ft. in diameter. On the E. side is a stone staircase by which access to this upper base is gained. The tower springs from this level. A parapet wall about 11 ft. thick at the top is built entirely around the upper base of the foundation to a height of 12 ft. Between this wall and the tower are the apartments of the keepers.
The tower rises from the base to a height of 115 ft., and is 50 ft. in diameter at the base; it diminishes in diameter as it ascends. The apartments of the tower are highly ornamented, and were not intended for occupation by the keepers. There are four stories, all of different orders of architecture, and adorned with busts and statues of kings of France and heathen gods. The material is stone. The basement or lower story appears to have been intended as a store room; the second story is called the king's apartments; the third is a chapel, and the fourth consists of a dome supported by columns, a kind of lower lantern; above this was originally a lantern formed of a stone dome and eight columns. The total height of the tower from its base to the upper point of the lantern dome was 146 ft., and from the rock 162 ft. In the upper lantern a fire of oak wood was kept burning at night for about 100 years, when, in 1717, the fire having weakened the stone supports by calcining them, the upper lantern was taken down and the light was kept up in the lower lantern. As it did not show well there, an iron lantern was erected in 1727 above this, in the place of the old stone lantern, and coal was used for fuel instead of wood.
It is worthy of remark that the upper part of this lantern contained an inverted cone, the base of which was the base of the lantern dome. The surface of the cone was covered with tin plates, thus forming a rude reflector that utilized a part of the light, which without it would have been lost. This was probably the first attempt made in a lighthouse to deviate the rays of light so as to throw to the horizon those which would have been lost in the upper parts of the atmosphere. The Cordouan lighthouse is also notable from the fact that the first Fresnel lens manufactured was placed in it in 1823. - The Eddystone lighthouse (see Eddystone Rocks) is celebrated on account of the difficulties attending its construction, and the fact that it is the type of all structures of the kind which have since been erected. The Eddystone rocks in the English channel, near the port of Plymouth, are in the fairway of all vessels coasting along the S. shore of England, and the attention of the government was directed to them at an early day. They are a cluster of gneiss rocks 600 or 700 ft. long from N. to S., with detached rocks covering about the same distance from E. to W. The highest part of the rock upon which the lighthouse is placed is about 16 ft. out of water at low water of spring tides.
The first lighthouse erected upon them was commenced in 1696 and finished in 1699 by Henry Winstanley. The accounts of its construction are vague, but it is supposed to have had a solid circular and polygonal stone base 12 ft. high and 24 ft. in diameter, upon which was built a structure of wood resembling a pagoda. The height from the rock to the base of the lantern was about 75 ft. The lantern was glazed. This building stood until November, 1703, when Mr. Winstanley went to the lighthouse with a party of workmen to make some repairs. On the 26th of the month a terrible storm arose, and not a remnant of the lighthouse nor a trace of its inmates was ever seen afterward. The fact that a lighthouse could be made to stand on the Eddystone having been demonstrated, soon after the destruction of Winstanley's building another was built by Rudyerd. It was commenced in 1706 and finished in 1709. It was an ingenious combination of wood and iron, and showed great advances in the art of engineering. The form was the frustum of a circular cone. It was built up nearly solid for a height of 27 ft. above the rock, the filling consisting of courses of cut stone alternating with courses of squared timber.
The outside casing was composed of 72 oak posts or uprights, the lower ends of which were fastened to the rock by heavy irons which were let into lewis holes. This is the first recorded application of the lewis for this use. The lantern was glazed. This building stood well with some repairs of the woodwork until December, 1755, when it was destroyed by fire. The fire commenced in the lantern in the early part of the night, and the keepers retreated from room to room until they reached the rock. Early in the morning they were brought to the shore, as the weather happened to be good enough to permit a boat to land on the rock. In 1756 Smea-ton was selected to rebuild the Eddystone. He determined to use stone for the material, and the shape of the trunk of a large tree as his model. The stones of a course were joined by dovetailing, and the different courses were connected by stone dowels. The upper surface of the rock was cut in horizontal steps, so that every course of masonry rests upon a horizontal bed. The general form of Smea-ton's structure is the frustum of a cone, or more strictly that of a solid of revolution formed by revolving a vertical plane bounded on one side by a concave curve around a vertical axis. The elevation, or a vertical section of the tower, indicates great strength.
The diameter of the lowest partial course is 32 ft., and that of the first or lowest entire course is 26 ft. The diameter of the course under the coping is 15 ft., and the whole height of the masonry is 77 ft. The tower is surmounted by a parapet wall 6 3/4 ft, high and 8 3/4 ft. in internal diameter. The combinations devised for obtaining the greatest strength in this tower by dovetailing, cramping, do welling, and by the use of hydraulic mortar, have never been surpassed. The experiments made by Smeaton on hydraulic cements in connection with the construction of this work were particularly valuable, and are still quoted. The erection of the lighthouse was, on account of its position, the difficulty of access to its site, and the fact that Smeaton had determined to build it of stone, attended with the greatest difficulties. The genius and energy of the engineer triumphed over all obstacles, and the work was finished in 1759. It has stood for more than 100 years, a monument of the skill of its designer and builder, and an example to all engineers. - Another noted lighthouse structure is the Bell Rock lighthouse off the E. coast of Scotland.
Fig. 8. Eddystone Lighthouse.
This rock is situated in the German ocean, 11m. from the Scottish coast, on the N. side of the frith of Forth, and nearly opposite that of Tay. It is about 427 ft. long and 230 ft. broad, but the vicinity is dangerous over an area of about 1,400 by 300 ft. The rock is a reddish sandstone, and the part upon which the lighthouse is built is 12 ft. below high water of spring tides, the rise of these tides being 16 ft. The lighthouse is built principally of sandstone found on the mainland in the vicinity, the outer ca sing of the lowest 30 ft. being of granite. It was commenced in 1807, and was finished late in 1810. The designers were Messrs. Rennie and Robert Stevenson, and it was constructed by the latter. The difficulties of the erection of this lighthouse were nearly as great as those encountered by Smeaton in his work, but the large size of the rock gave it an advantage, and Smeaton's experience was made useful by Stevenson in its construction. The form is similar to that of the Eddystone. The diameter of the bottom course is 42 ft., and that of the course just below the cornice 15 ft. The stone work is 102 1/2- ft. high, in which height is included that of a parapet wall, octagonal in plan, which surmounts the tower.
This wall is 6 ft. high, and its sides are 5 1/2 ft. long; upon it the lantern is placed. The account of the erection of this lighthouse, written by Mr. Stevenson and published in 1824, contains an accurate history of the Scottish lighthouses. - The Skerryvore lighthouse, off the W. coast of Scotland, is also notable on account of the difficulties of its construction. The Skerryvore rocks are situated about 11m. S. W. of the island of Tyree, and 50 m. from the mainland. They are in the track of large vessels bound from the Clyde and Mersey (Glasgow and Liverpool) around the north of Ireland, and many wrecks have taken place upon them. The erection of a lighthouse was authorized in 1814, but it was not till 1834 that a survey was made, the result of which was the discovery of a solid gneiss rock 160 ft. long and 70 ft. wide, upon which it was determined to erect the lighthouse. Alan Stevenson, a son of the constructor of the Bell Rock lighthouse, succeeded his father as engineer of the commissioners of northern lights, and to him was committed the difficult task of the erection of the Skerryvore lighthouse. The form chosen for the tower is a shaft surmounted by a belt and capital, upon which is the parapet wall.
The shaft is a solid of revolution formed by revolving a rectangular hyperbola about its asymptote. The diameter of the lowest course is 42 ft., that of the top course 1G ft., and the whole height is 138 ft. The tower for a height of 26 ft. is solid. Immediately above the solid part the walls are 9 1/2 ft. thick, and they gradually diminish from this thickness to 2 ft. The material is granite, and the tower is surmounted by a bronze lantern in which is placed a Fresnel lens of the first order, showing a revolving light. The work was commenced in 1839, and the light was first shown in February, 1844. An account of the construction of the work has been published by Mr. Stevenson, which is valuable not only for the description of this particular work, but because it contains a dissertation on the Fresnel system of lighthouse illumination, and a succinct history of lighthouses. Figs. 8, 9, and 10 show the comparative sizes and shapes of the Eddystone, Bell Rock, and Skerryvore lighthouses. The high and low waters of ordinary tides are indicated on the figures, and the letter G gives the position of the centre of gravity of each tower. - A cast-iron lighthouse for the Great Isaac's rocks, near Bermuda, was completed in 1856, by order of the English admiralty.
The tower is 120 ft. high from the base to the plane on which the lantern rests, and 150 ft. to the top of the lantern. At the base the tower is 25 ft. in diameter, and at the top 14 ft. One of the great peculiarities of the construction is that the 155 large cast-iron plates of which it is composed are not placed horizontally round the tower, as heretofore in erections of a similar kind, but in what is technically called " break-joints;" i. e., the plates, so to speak, are dovetailed and wedged the one into the other, in such a manner as to form a perfect column, and equal in strength in all its parts. - Other noted lighthouses have been erected upon the coasts of Europe, but those described are all whose constructions have been given in detail and published to the world, and are types of all others. Some on the coasts of France are as bold in their execution and as difficult in their construction as any noticed above. - Many of the lighthouses in the United States are unsurpassed by any in the world, and are of exceedingly difficult construction. The most noted is that of Minot's Ledge off the coast of Massachusetts. This rock is the outer one of a ledge lying off the town of Cohasset. It is situated about 8 m.
E. S. E. of Boston light, and is a projecting point very dangerous to vessels coming into Boston from seaward. Should these vessels have a N. E. wind, and by any chance miss the entrance to the harbor, they would be almost certainly cast away on these rocks were there1 no signal placed there to warn them off. It is about 1 1/2 m. from the nearest land, and at low water the highest part of the rock (a circle about 25 ft. in diameter) is bare. The rise of spring tides is not far from 12 ft., so that no part of the rock is ever uncovered more than a few minutes. The difficulties of erecting a lighthouse on this rock were very great. Attention was drawn to the dangers of this point many years ago, and in 1847 an appropriation was made by congress for the construction of a lighthouse on the rock. It was determined to erect an iron-pile structure, at the top of which was to be the keepers' dwelling, and this was to be surmounted by the lantern enclosing the illuminating apparatus. The plan of the work was a regular octagon, each side of which at the base was 9 1/2 ft., the diameter of the circumscribing circle being 25 ft. Iron piles 10 in. in diameter where they leave the rock were inserted 5 ft. into it, at each angle of the octagon and at its centre.
These were firmly braced and tied together by wrought-iron braces. At a height of 55 ft. above the highest point of the rock the heads of the piles were firmly secured to a heavy casting. Above this casting the floor of the dwelling was placed. The structure was finished in the autumn of 1849, and stood until April, 1851, when it was carried away by one of the most terrific storms that have ever occurred on the Atlantic coast. All of the iron piles were twisted off at short distances above their feet. One cause of the destruction of this lighthouse is supposed to have been a hawser which was fastened to the top of the structure at one end, the other being anchored in the sea. The waves after leaving the lighthouse would strike the hawser, and the effect of the blow was transmitted to the pyramid with very great leverage, causing a tendency to oscillate. Another cause was the ice which froze to the piles, and thus increased the extent of surface exposed to the action of the sea. In 1852 congress appropriated money for rebuilding the lighthouse, and a design was originated by the lighthouse board and approved by the secretary of the treasury early in 1855. It is a granite tower in the shape of the frustum of a cone.
The base is 30 ft. in diameter, and the whole height of the stonework is 88 ft. The lower 40 ft. are solid. The remainder of the tower is made up of keepers' apartments, store rooms, and the parapet, which encloses the pedestal of the lens apparatus. The stones of the courses are dovetailed in the securest manner, and the courses are fastened to each other by galvanized wrought-iron dowels, 3 in. in diameter. The work was commenced early in the season of 1855, and an idea of the difficulties to be overcome may be formed from the fact that although advantage was taken of every moment in which it was possible to work upon the rock, it was not until the last part of the season of 1857 that any stones were laid, the whole of the intervening time having been taken up in levelling the foundation bed. In the season of 1857 four stones were laid, in 1858 six entire courses were laid, and in 1859 the whole of the solid portion of the structure and half of the remainder, making a total height of 60 ft., were placed. The lighthouse was finished and lighted at the end of 1860. - The early history of lighthouses in the United States is involved in obscurity.
All built prior to 1789 were ceded to the federal government by the respective states near the time of the adoption of the federal constitution, and the records of the erection and maintenance of the lighthouses before that date are buried among the archives of the several states. It is known, however, that the ports of Portland, Portsmouth, and Newburyport, Cape Ann, Boston, Plymouth, Nantucket, Newport, New London, New York, the capes of the Delaware, the capes of the Chesapeake, the port of Charleston, and the mouth of the Savannah river were all lighted before 1789. The buildings were generally rough stone or wood towers surmounted by large iron lanterns. With few exceptions they have all been rebuilt. They were generally of small height, and the illuminating apparatus was of the rudest description. A new impulse was given to lighthouses in the United States about the year 1845, when a commission consisting of two officers of the navy was sent abroad to examine the lighthouse establishments of European governments. About the same time Mitchell's screw pile was introduced, and the style of reflectors and lamps was much improved.
The buildings too were more substantially erected, and more attention was paid to the principle that the light should be brought to the horizon, which when reflectors were first introduced was lost sight of almost entirely. About the year 1852 the general introduction of the lens or Fresnel system of lighthouse illumination was commenced, and all the lighthouses of the United States are now furnished with this apparatus. Under the lighthouse board the principle has been adopted of building all first class lighthouses of fire-proof materials. Although under this system the first cost of the structure is large, an insignificant outlay only is necessary for repairs. The same system obtains in the smaller lighthouses when the amount available for their erection will permit it, but in harbor and pierhead lights light wood or iron structures are erected, which can be rebuilt at a small cost in case of serious damage. On June 30, 1873, there were 641 light stations on the coasts of the United States, including the Atlantic, Pacific, gulf, and lake coasts, and the shores of the various bays, sounds, and rivers. Of these, 620 are lighthouses and 21 light vessels.
The expenditures on account of the maintenance of the lighthouse establishment for the fiscal year ending June 30, 1875, are estimated as follows:
Fig. 9. Bell Rock Lighthouse.
Fig. 10. - Skerryvore Lighthouse.
Buoys and beacons.......
The number of buoys and beacons in the waters of the United States is about 3,000. The buoys must be shifted, cleaned, and painted every season, and those which are in exposed positions are frequently carried away by heavy seas or ice. The cost of keeping these aids to navigation in an efficient state is no small item in the annual expense of the establishment. - In all governments except that of the United States, commerce is directly or indirectly made to pay for the expense of the lighthouse establishments. In Great Britain a tax is laid upon every vessel, domestic or foreign, that uses the particular light which is to be supported. In some countries a light due is levied, which is constant whether one or more lights have been used by the vessel. In others, as France for instance, a harbor due or tax is levied, with the proceeds of which the lights are kept up, but the necessary amount is appropriated from the public treasury. The tax is always a severe exaction and restriction upon commerce, and it is to be regretted that foreign governments do not in this instance follow the example of the United States, which supports its lighthouse establishment without any tax upon vessels, domestic or foreign.
The foreign vessels reap the benefit of our policy, but the favor is not returned to United States vessels. In Great Britain the lights are in charge of three corporations. Those of England are under the Trinity board; those of Scotland and the adjacent islands are under the commissioners of northern lights; and those of Ireland are under the Dublin ballast board. These corporations determine as to the erection or discontinuance of lights in their respective jurisdictions, have entire control of the personnel, fixtures, and expenditures of the establishment, and determine the tax to be laid upon vessels which pass or use the lights. The funds raised by this tax are devoted to the annual maintenance and improvement of the lights, though in the case of the Trinity board a part of them may be used for the maintenance of pensioners belonging to the board. In its original construction it is believed this board had nothing to do with the general lighthouse system of England. In France the lighthouse establishment is governed by a mixed board of officers of the corps des ponts et chaussees, naval officers, and scientific civilians, and is presided over by the minister of public works.
The expense of the maintenance of the establishment is paid by the government, but, as before stated, a tonnage tax is laid upon all vessels, the proceeds of which are expended in the construction and repair of piers, breakwaters, lighthouses, etc. In the other countries of Europe the lighthouse establishments are all connected with the governments, and are managed in various ways. In Russia, Sweden, Denmark, Belgium, and the states bordering upon the Mediterranean, they are generally under the charge of the navy departments. In the United States the establishment is under the control of a board, consisting of two officers of the navy, two officers of army engineers, two civilians of high scientific attainments, and an officer of the navy as secretary. The secretary of the treasury is ex officio president of this board, and its decisions are in all cases subject to his control. The lighthouse establishment is therefore a branch of the treasury department, and its annual expenses are estimated for by that department. For the proper administration of the affairs of the establishment, the coasts of the United States are divided into 13 lighthouse districts. To each of these districts is assigned an inspector, who is detailed from the officers of army engineers and the navy.
These inspectors have the control of the operations of the establishment in their respective districts (with the exception of the appointment of light keepers), and correspond directly with the lighthouse board. They are furnished with steamers in which they make quarterly inspections of the light stations in their districts, and which are also used for taking care of buoys. They are required to make annual reports of the condition of their districts, in which are embodied their recommendations of new lights, etc, for the action of the lighthouse board. The construction of new lighthouses and important repairs of old ones are carried on under the direction of officers of the corps of army engineers, who are detailed for this service. The routine duties of the board are discharged by two secretaries, one of whom is an officer of the navy, and the other an officer of the corps of army engineers. Meetings of the board are held weekly for the transaction of the routine or any other business that may be brought before it by the action of the treasury department.
The meetings are held at Washington, where the office of the board is situated.