SOUND SIGNALS.
In Appleton's "Annual Cyclopædia" for 1883, Mr. Arnold B. Johnson, Chief Clerk of the Lighthouse Board, contributes a mass of very interesting information, under the above title. His descriptions of the most approved inventions relating thereto are interesting, and we make the following extracts:
The sound signals generally used to guide mariners, especially during fogs, are, with certain modifications, sirens, trumpets, steam-whistles, bell-boats, bell-buoys, whistling buoys, bells struck by machinery, cannons fired by powder or gun cotton, rockets, and gongs.
Gongs.—Gongs are somewhat used on lightships, especially in British waters. They are intended for use at close quarters. Leonce Reynaud, of the French lighthouse service, has given their mean effective range as barely 550 yards. They are of most use in harbors, short channels, and like places, where a long range would be unnecessary. They have been used but little in United States waters. The term "effective range" is used here to signify the actual distance at which, under the most unfavorable circumstances, a signal can generally be heard on board of a paddle-wheel steamer in a heavy sea-way.
Guns.—The use of guns is not so great as it once was. Instances are on record in which they were quite serviceable. Admiral Sir A. Milne said he had often gone into Halifax harbor, in a dense fog like a wall, by the sound of the Sambro fog gun. But in the experiments made by the Trinity House off Dungeness in January, 1864, in calm weather, the report of an eighteen-pounder, with three pounds of powder, was faint at four miles. Still, in the Trinity House experiments of 1865, made in light weather with a light gun, the report was clearly heard seven miles away. Dr. Gladstone records great variability in the range of gun-sound in the Holyhead experiments. Prof. Henry says that a twenty-four-pounder was used at Point Boneta, San Francisco Bay, Cal., in 1856-57, and that, by the help of it alone, vessels came into the harbor during the fog at night as well as in the day, which otherwise could not have entered. The gun was fired every half hour, night and day, during foggy and thick weather in the first year, except for a time when powder was lacking. During the second year there were 1,582 discharges. It was finally superseded by a bell-boat, which in its turn was after a time replaced by a siren. A gun was also used at West Quoddy Head, Maine. It was a carronade, five feet long, with a bore of five and one-quarter inches, charged with four pounds of powder. The gun was fired on foggy days when the Boston steamer was approaching the lighthouse from St. Johns, and the firing was begun when the steamer's whistle was heard, often when she was six miles away, and was kept up as fast as the gun could be loaded, until the steamer answered with its whistle.
The report of the gun was heard from two to six miles. "This signal was abandoned," Prof. Henry says, "because of the danger attending its use, the length of intervals between successive explosions, and the brief duration of the sound, which renders it difficult to determine its direction with accuracy." In 1872 there were three fog guns on the English coast, iron eighteen-pounders, carrying a three pound charge of powder, which were fired at intervals of fifteen minutes in two places, and of twenty minutes in the other. The average duration of fog at these stations was said to be about six hours, and as it not unfrequently lasted twenty hours, each gun required two gunners, who had to undergo severe labor, and the risk of remissness and irregularity was considerable. In 1881 the interval between charges was reduced to ten minutes.
The Trinity House, in its experiments at South Foreland, found that the short twenty-four pound howitzer gave a better sound than the long eighteen-pounder. Tyndall, who had charge of the experiments, sums up as to the use of the guns as fog-signals by saying: "The duration of the sound is so short that, unless the observer is prepared beforehand, the sound, through lack of attention rather than through its own powerlessness, is liable to be unheard. Its liability to be quenched by local sound is so great that it is sometimes obliterated by a puff of wind taking possession of the ears at the time of its arrival. Its liability to be quenched by an opposing wind, so as to be practically useless at a very short distance to windward, is very remarkable.... Still, notwithstanding these drawbacks, I think the gun is entitled to rank as a first-class signal."
The minute gun at sea is known the world over as a signal of distress. The English lightships fire guns to attract the attention of the lifeboat crew when shipwrecks take place in sight of the ships, but out of sight of the boats; and guns are used as signals of approaching floods at freshet times in various countries.
Rockets.—As a signal in rock lighthouses, where it would be impossible to mount large pieces of apparatus, the use of a gun-cotton rocket has been suggested by Sir Richard Collinson, deputy-master of the Trinity House. A charge of gun-cotton is inclosed in the head of a rocket, which is projected to the height of perhaps 1,000 feet, when the cotton is exploded, and the sound shed in all directions. Comparative experiments with the howitzer and rocket showed that the howitzer was beaten by a rocket containing twelve ounces, eight ounces, and even four ounces of gun-cotton. Large charges do not show themselves so superior to small charges as might be expected. Some of the rockets were heard at a distance of twenty-five miles. Tyndall proposes to call it the Collinson rocket, and suggests that it might be used in lighthouses and lightships as a signal by naval vessels.
Bells.—Bells are in use at every United States lightstation, and at many they are run by machinery actuated by clock-work, made by Mr. Stevens, of Boston, who, at the suggestion of the Lighthouse Board, has introduced an escapement arrangement moved by a small weight, while a larger weight operates the machinery which strikes the bell. These bells weigh from 300 to 3,000 pounds. There are about 125 in use on the coasts of the United States. Experiments made by the engineers of the French Lighthouse Establishment, in 1861-62, showed that the range of bell-sounds can be increased with the rapidity of the bell-strokes, and that the relative distances for 15, 25, and 60 bell-strokes a minute were in the ratio of 1, 1-14/100, and 1-29/100. The French also, with a hemispherical iron reflector backed with Portland cement, increased the bell range in the ratio of 147 to 100 over a horizontal arc of 60°, beyond which its effect gradually diminished. The actual effective range of the bell sound, whatever the bell size, is comparatively short, and, like the gong, it is used only where it needs to be heard for short distances. Mr. Cunningham, Secretary of the Scottish Lighthouse Establishment, in a paper on fog signals, read in February, 1863, says the bell at Howth, weighing 2¼ tons, struck four times a minute by a 60 pound hammer falling ten inches, has been heard only one mile to windward against a light breeze during fog; and that a similar bell at Kingston, struck eight times a minute, had been so heard three miles away as to enable the steamer to make her harbor from that distance. Mr. Beaseley, C.E., in a lecture on coast-fog signals, May 24, 1872, speaks of these bells as unusually large, saying that they and the one at Ballycottin are the largest on their coasts, the only others which compare with them being those at Stark Point and South Stack, which weigh 31¾ cwt. and 41½ cwt. respectively. Cunningham, speaking of the fog-bells at Bell Rock and Skerryvore lighthouses, says he doubts if either bell has been the means of saving a single vessel from wreck during fog, and he does not recall an instance of a vessel reporting that she was warned to put about in the fog, or that she ascertained her position in any respect by hearing the sound of the bell in either place. Gen. Duane, U.S.A., says a bell, whether operated by hand or machinery, cannot be considered an efficient fog signal on the sea-coast. In calm weather it cannot be heard half the time at a greater distance than one mile, while in rough weather the noise of the surf will drown its sound to seaward altogether. The use of bells is required, by the International Code, on ships of all nations, at regular intervals during fog. But Turkish ships are allowed to substitute the gong or gun, as the use of bells is forbidden to the followers of Mohammed.
FIG. 1.—COURTENAY'S WHISTLING BUOY.
Whistling Buoys.—The whistling buoy now in use was patented by Mr. J.M. Courtenay, of New York. It consists of an iron pear-shaped bulb, 12 feet across at its widest part, and floating 12 feet out of water. Inside the bulb is a tube 33 inches across, extending from the top through the bottom to a depth of 32 feet, into water free from wave motion. The tube is open at its lower end, but projects, air-tight, through the top of the bulb, and is closed with a plate having in it three holes, two for letting the air into the tube, and one between the others for letting the air out to work the 10-inch locomotive whistle with which it is surmounted. These holes are connected with three pipes which lead down to near the water level, where they pass through a diaphragm which divides the outer cylinder into two parts. The great bulb which buoys up the whole mass rises and falls with the motion of the waves, carrying the tube up and down with it, thus establishing a piston-and-cylinder movement, the water in the tube acting as an immovable piston, while the tube itself acts as a moving cylinder. Thus the air admitted through valves, as the buoy rises on the wave, into that part of the bulb which is above water, is compressed, and as the buoy falls with the wave, it is further compressed and forced through a 2½ inch pipe which at its apex connects with the whistle. The dimensions of the whistling buoy have recently been much diminished without detracting materially from the volume of sound it produces. It is now made of four sizes. The smallest in our waters has a bulb 6 feet in diameter and a tube 10 feet in length, and weighs but 2,000 pounds. The largest and oldest whistling buoy has a 12-foot bulb, a tube 32 feet long, and weighs 12,000 pounds.
There are now 34 of these whistling buoys on the coast of the United States, which have cost, with their appurtenances, about $1,200 each. It is a curious fact that, in proportion as they are useful to the mariner, they are obnoxious to the house dweller within earshot of them, and that the Lighthouse Board has to weigh the petitions and remonstrances before setting these buoys off inhabited coasts. They can at times be heard 15 miles, and emit an inexpressibly mournful and saddening sound.
The inspector of the First Lighthouse District, Commander Picking, established a series of observations at all the light stations in the neighborhood of the buoys, giving the time of hearing it, the direction of the wind, and the state of the sea, from which it appears that in January, 1878, one of these buoys was heard every day at a station 1⅛ miles distant, every day but two at one 2¼ miles distant, 14 times at one 7½ miles distant, and 4 times at one 8½ miles distant. It is heard by the pilots of the New York and Boston steamers at a distance of one-fifth of a mile to 5 miles, and has been frequently heard at a distance of 9 miles, and even, under specially favorable circumstances, 15 miles.
The whistling buoy is also used to some extent in British, French, and German waters, with good results. The latest use to which it has been put in this country has been to place it off the shoals of Cape Hatteras, where a light ship was wanted but could not live, and where it does almost as well as a light ship would have done. It is well suited for such broken and turbulent waters, as the rougher the sea the louder its sound.
FIG. 2.—BROWN'S BELL BUOY.
Bell-Buoys.—The bell-boat, which is at most a clumsy contrivance, liable to be upset in heavy weather, costly to build, hard to handle, and difficult to keep in repair, has been superseded by the Brown bell-buoy, which was invented by the officer of the lighthouse establishment whose name it bears. The bell is mounted on the bottom section of an iron buoy 6 feet 6 inches across, which is decked over and fitted with a framework of 3-inch angle-iron 9 feet high, to which a 300-pound bell is rigidly attached. A radial grooved iron plate is made fast to the frame under the bell and close to it, on which is laid a free cannon-ball. As the buoy rolls on the sea, this ball rolls on the plate, striking some side of the bell at each motion with such force as to cause it to toll. Like the whistling-buoy, the bell-buoy sounds the loudest when the sea is the roughest, but the bell-buoy is adapted to shoal water, where the whistling-buoy could not ride; and, if there is any motion to the sea, the bell-buoy will make some sound. Hence the whistling-buoy is used in roadsteads and the open sea, while the bell-buoy is preferred in harbors, rivers, and the like, where the sound-range needed is shorter, and smoother water usually obtains. In July, 1883, there were 24 of these bell-buoys in United States waters. They cost, with their fitments and moorings, about $1,000 each.
Locomotive-Whistles.—It appears from the evidence given in 1845, before the select committee raised by the English House of Commons, that the use of the locomotive-whistle as a fog-signal was first suggested by Mr. A. Gordon, C.E., who proposed to use air or steam for sounding it, and to place it in the focus of a reflector, or a group of reflectors, to concentrate its sounds into a powerful phonic beam. It was his idea that the sharpness or shrillness of the whistle constituted its chief value. And it is conceded that Mr. C.L. Daboll, under the direction of Prof. Henry, and at the instance of the United States Lighthouse Board, first practically used it as a fog-signal by erecting one for use at Beaver Tail Point, in Narragansett Bay. The sounding of the whistle is well described by Price-Edwards, a noted English lighthouse engineer, "as caused by the vibration of the column of air contained within the bell or dome, the vibration being set up by the impact of a current of steam or air at a high pressure." It is probable that the metal of the bell is likewise set in vibration, and gives to the sound its timbre or quality. It is noted that the energy so excited expends its chief force in the immediate vicinity of its source, and may be regarded, therefore, as to some extent wasted. The sound of the whistle, moreover, is diffused equally on all sides. These characteristics to some extent explain the impotency of the sound to penetrate to great distances. Difference in pitch is obtained by altering the distance between the steam orifice and the rim of the drum. When brought close to each other, say within half an inch, the sound produced is very shrill, but it becomes deeper as the space between the rim and the steam or air orifice is increased.
Prof. Henry says the sound of the whistle is distributed horizontally. It is, however, much stronger in the plane containing the lower edge of the bell than on either side of this plane. Thus, if the whistle is standing upright in the ordinary position, its sound is more distinct in a horizontal plane passing through the whistle than above it or below it.
The steam fog-whistle is the same instrument ordinarily used on steamboats and locomotives. It is from 6 to 18 inches in diameter, and is operated by steam under a pressure of from 50 to 100 pounds. An engine takes its steam from the same boiler, and by an automatic arrangement shuts off and turns on the steam by opening and closing its valves at determined times. The machinery is simple, the piston-pressure is light, and the engine requires no more skilled attention than does an ordinary station-engine.
"The experiments made by the Trinity House in 1873-74 seem to show," Price-Edwards says, "that the sound of the most powerful whistle, whether blown by steam or hot air, was generally inferior to the sound yielded by other instruments," and consequently no steps were taken to extend their use in Great Britain, where several were then in operation. In Canadian waters, however, a better result seems to have been obtained, as the Deputy Minister of Marine and Fisheries, in his annual report for 1872, summarizes the action of the whistles in use there, from which it appears that they have been heard at distances varying with their diameter from 3 to 25 miles.
The result of the experiments made by Prof. Henry and Gen. Duane for the United States Lighthouse Board, reported in 1874, goes to show that the steam-whistle could be heard far enough for practical uses in many positions. Prof. Henry found that he could hear a 6-inch whistle 7¼ miles with a feeble opposing wind. Gen. Duane heard the 10-inch whistle at Cape Elizabeth at his house in Portland, Maine, nine miles distant, whenever it was in operation. He heard it best during a heavy northeast snow storm, the wind blowing then directly from him, and toward the source of the sound. Gen. Duane also reported that "there are six fog-signals on the coast of Maine; these have frequently been heard at the distance of twenty miles," ... which distance he gives as the extreme limit of the twelve-inch steam-whistle.
Trumpets.—The Daboll trumpet was invented by Mr. C.L. Daboll, of Connecticut, who was experimenting to meet the announced wants of the United States Lighthouse Board. The largest consists of a huge trumpet seventeen feet long, with a throat three and one-half inches in diameter, and a flaring mouth thirty-eight inches across. In the trumpet is a resounding cavity, and a tongue-like steel reed ten inches long, two and three-quarter inches wide, one inch thick at its fixed end, and half that at its free end. Air is condensed in a reservoir and driven through the trumpet by hot air or steam machinery at a pressure of from fifteen to twenty pounds, and is capable of making a shriek which can be heard at a great distance for a certain number of seconds each minute, by about one-quarter of the power expended in the case of the whistle. In all his experiments against and at right angles and at other angles to the wind, the trumpet stood first and the whistle came next in power. In the trial of the relative power of various instruments made by Gen. Duane in 1874, the twelve-inch whistle was reported as exceeding the first-class Daboll trumpet. Beaseley reports that the trumpet has done good work at various British stations, making itself heard from five to ten miles. The engineer in charge of the lighthouses of Canada says: "The expense for repairs, and the frequent stoppages to make these repairs during the four years they continued in use, made them [the trumpets] expensive and unreliable. The frequent stoppages during foggy weather made them sources of danger instead of aids to navigation. The sound of these trumpets has deteriorated during the last year or so." Gen. Duane, reporting as to his experiments in 1881, says: "The Daboll trumpet, operated by a caloric engine, should only be employed in exceptional cases, such as at stations where no water can be procured, and where from the proximity of other signals it may be necessary to vary the nature of the sound." Thus it would seem that the Daboll trumpet is an exceptionally fine instrument, producing a sound of great penetration and of sufficient power for ordinary practical use, but that to be kept going it requires skillful management and constant care.
The Siren.—The siren was adapted from the instrument invented by Cagniard de la Tour, by A. and F. Brown, of the New York City Progress Works, under the guidance of Prof. Henry, at the instance and for the use of the United States Lighthouse Establishment, which also adopted it for use as a fog-signal. The siren of the first class consists of a huge trumpet, somewhat of the size and shape used by Daboll, with a wide mouth and a narrow throat, and is sounded by driving compressed air or steam through a disk placed in its throat. In this disk are twelve radial slits; back of the fixed disk is a revolving plate, containing as many similar openings. The plate is rotated 2,400 times each minute, and each revolution causes the escape and interruption of twelve jets of air or steam through the openings in the disk and rotating plate. In this way 28,800 vibrations are given during each minute that the machine is operated; and, as the vibrations are taken up by the trumpet, an intense beam of sound is projected from it. The siren is operated under a pressure of seventy-two pounds of steam, and can be heard, under favorable circumstances, from twenty to thirty miles. "Its density, quality, pitch, and penetration render it dominant over such other noises after all other signal-sounds have succumbed." It is made of various sizes or classes, the number of slits in its throat-disk diminishing with its size. The dimensions given above are those of the largest. [See engraving on page 448, "Annual Cyclopædia" for 1880.]
The experiments made by Gen. Duane with these three machines show that the siren can be, all other things being equal, heard the farthest, the steam-whistle stands next to the siren, and the trumpet comes next to the whistle. The machine which makes the most noise consumes the most fuel. From the average of the tests it appears that the power of the first-class siren, the twelve-inch whistle, and first-class Daboll trumpet are thus expressed: siren nine, whistle seven, trumpet four; and their relative expenditure of fuel thus: siren nine, whistle three, trumpet one.
Sound-signals constitute so large a factor in the safety of the navigator, that the scientists attached to the lighthouse establishments of the various countries have given much attention to their production and perfection, notably Tyndall in England and Henry in this country. The success of the United States has been such that other countries have sent commissions here to study our system. That sent by England in 1872, of which Sir Frederick Arrow was chairman, and Captain Webb, R.N., recorder, reported so favorably on it that since then "twenty-two sirens have been placed at the most salient lighthouses on the British coasts, and sixteen on lightships moored in position where a guiding signal is of the greatest service to passing navigation."
The trumpet, siren, and whistle are capable of such arrangement that the length of blast and interval, and the succession of alternation, are such as to identify the location of each, so that the mariner can determine his position by the sounds.
In this country there were in operation in July, 1883, sixty-six fog-signals operated by steam or hot air, and the number is to be increased in answer to the urgent demands of commerce.
Use of Natural Orifices.—There are, in various parts of the world, several sound-signals made by utilizing natural orifices in cliffs through which the waves drive the air with such force and velocity as to produce the sound required. One of the most noted is that on one of the Farallon Islands, forty miles off the harbor of San Francisco, which was constructed by Gen. Hartmann Bache, of the United States Engineers, in 1858-59, and of which the following is his own description:
"Advantage was taken of the presence of the working party on the island to make the experiment, long since contemplated, of attaching a whistle as a fog-signal to the orifice of a subterranean passage opening out upon the ocean, through which the air is violently driven by the beating of the waves. The first attempt failed, the masonry raised upon the rock to which it was attached being blown up by the great violence of the wind-current. A modified plan with a safety-valve attached was then adopted, which it is hoped will prove permanent. ... The nature of this work called for 1,000 bricks and four barrels of cement."
Prof. Henry says of this:
"On the apex of this hole he erected a chimney which terminated in a tube surmounted by a locomotive-whistle. By this arrangement a loud sound was produced as often as the wave entered the mouth of the indentation. The penetrating power of the sound from this arrangement would not be great if it depended merely on the hydrostatic pressure of the waves, since this under favorable circumstances would not be more than that of a column of water twenty feet high, giving a pressure of about ten pounds to the square inch. The effect, however, of the percussion might add considerably to this, though the latter would be confined in effect to a single instance. In regard to the practical result from this arrangement, which was continued in operation for several years, it was found not to obviate the necessity of producing sounds of greater power. It is, however, founded on an ingenious idea, and may be susceptible of application in other cases."
There is now a first-class siren in duplicate at this place.
The sixty-six steam fog-signals in the waters of the United States have been established at a cost of more than $500,000, and are maintained at a yearly expense of about $100,000. The erection of each of these signals was authorized by Congress in an act making special appropriations for its establishment, and Congress was in each instance moved thereto by the pressure of public opinion, applied usually through the member of Congress representing the particular district in which the signal was to be located. And this pressure was occasioned by the fact that mariners have come to believe that they could be guided by sound as certainly as by sight. The custom of the mariner in coming to this coast from beyond the seas is to run his ship so that on arrival, if after dark, he shall see the proper coast-light in fair weather, and, if in thick weather, that he shall hear fog-signal, and, taking that as a point of departure, to feel his way from the coast-light to the harbor-light, or from the fog-signal on the coast to the fog-signal in the harbor, and thence to his anchorage or his wharf. And the custom of the coaster or the sound-steamer is somewhat similar.