Popular Science Monthly/Volume 33/May 1888/Sound-Signals at Sea
|SOUND-SIGNALS AT SEA.|
By ARNOLD BURGES JOHNSON.
THE difficulty in determining the true and exact direction of the sounds we hear meets us in various ways. The hunter hears the note of a bird, the hiss or whistle of a deer, and the sound indicates identity and proximity but not direction. The hunter waits for repeated renewal of the sound to ascertain its exact position, and even then verifies his audition by his vision. The hunter by his camp-fire may aim between the luminous dots of reflected light, which he knows to be the eyes of a wolf; but he would scarcely be able to aim at or even very near that spot on simply hearing the howl from the wolf that owns the eyes.
The plainsman hears a shout in the distance. He may recognize it as the voice of a comrade, and fix the general direction as north, east, south, or west, but hardly more. He may shout back, and the two may come together; but if it be dark and there is no fire or other signal, the shouting back and forth must be frequently repeated, and varied from a simple to a complex sound, that each may correct the error of his own audition, eliminate his personal equation, and the sound will appear to swing, pendulum-like, right and left, with shorter and shorter stroke, till the comrades come together.
The average child, returning from school, on entering the house calls, "Mamma!" The mother, perhaps, replies, "Yes!" "Where are you?" is the next question, and the reply informs the child not only as to the floor, but as to the room in which the mother can be found. The child can not determine its mother's location by the sound of her voice. This exaggerated instance may be owing to the reflection of the sound, not only from the walls, but from the strata of air differing in temperature and humidity.
How many of us going to the next street, running at right angles to the car-tracks, can tell, from hearing the bell of the approaching street-car before the car comes in sight, whether that car is going north or south? It does not seem that animals can determine the direction of sound much better than man. The sleeping dog, roused by his master's call, is all abroad as to his master's location, and determines it by sight or scent, or both, frequently running in several different directions before hitting the right one. The deer, on being startled by the unseen hunter's tread, is not always right in his selection of the route to get out of harm's way. A flock of geese, ducks, or other birds, on hearing a gun, is as likely to fly toward as from the sportsman, if he has kept entirely out of sight, and the flash of his piece has not been seen.
It is a question whether the blind are better able to determine the direction of sound by ear than are seeing people. It is possible that their senses of touch and smell are so highly developed that their instantaneous action with that of the ear give them a decided advantage over seeing people in this matter. I have known a blind man to be so sensible of the current of air put in motion by the speaking of a single word in a room, that he could select the speaker by his location, though others were present. So, too, I have known a blind man to locate and identify the various people in the room, he saying he did it by the different scent evolved from each, the seeing people there not being sensible of any scent from any one. And yet he, when standing in the middle of the room with his nose stopped, could not give the direction of one single speaking person.
Prof. Alexander Graham Bell reports, in a paper he read before the American Association for the Advancement of Science at Saratoga in 1879, a series of experiments in binaural audition, showing, among other things, that direction can not be appreciated by monaural observation; that when the source of sound is at the nadir of the observer, the perception of its direction is absolutely unreliable, and that not one of the many on whom he tried the experiment had the slightest idea of the true direction of a sound produced beneath him.
We are so much accustomed to the aid of our other senses, especially that of sight, that we incline to give more value to audition in determining direction than it deserves. That is one reason why we err so largely when so placed that the eye can not correct the error of the ear—in fact, many people seem to be unaware that they have any inability to locate sound by the ear until they have learned the fact by experience, and even then they appear to consider marked instances as abnormal.
It is sufficiently easy to account for aberrations of audition as to the direction of sound from objective causes, such as reflection, diffraction, and deflection of sound-waves. But it may also often be accounted for by what Prof. Henry called subjective causes, such as induce belief that an anticipated sound has come from a specified direction, when it has really come from quite another direction. Here the personal equation of the listener must be largely taken into consideration. The success of the ventriloquist may also depend upon subjective causes.
President Welling tells us something of how Prof. Henry, when at Princeton, induced subjective causes in his pupils, to their bewilderment, making them believe, for the moment, that a given sound came from a specified corner of the class-room, when it really came from quite a different direction.
Mariners are beginning to accept the fact that they may err in assigning the true direction to sound; but their ideas on the subject are still vague and indeterminate. Hence occur collisions between ships at sea, and lawsuits between their owners on shore. The collision at 10 p. m., on September 21, 1882, between the Dutch steamer Edam and the British steamer Lepanto, on George's Bank, Atlantic Ocean, when the former was sunk by the latter, resulted in a suit in the United States District Court at New York city, in which the case turned on an erroneous location of the Edam by the Lepanto, on hearing the sound of her fog-horn. The court dismissed the case with costs, holding that "an error of five points in locating a vessel's position by the sound of her whistle in a fog is not necessarily a fault under the proved aberrations in the course of sound." The judge, in his decision, quotes, among others, papers read before the Washington Philosophical Society as his authority for certain statements he makes as to these laws of sound bearing on the case.
As it seems evident that the unassisted ear is likely to err in determining the location of sound, the question arises, Can the ear be aided in this matter? Apparently this is possible. Prof. Mayer, of the Institute of Technology at Hoboken, N. J., has, to a certain extent, solved this problem by the construction of an instrument called the "topophone," by the use of which President Morton, a member of the Lighthouse Board, was enabled to locate within ten degrees, or less than one compass-point, the sound of a fog-signal, when in the cabin of a steamer at sea, seven miles away, and that, too, after he had purposely deprived himself of a knowledge of even the direction of the shore by having the steamer turned in her course from time to time. President Morton describes it thus:
The principle upon which the operation of this apparatus depends was first announced by Prof. Mayer in 1872 (see "American Journal of Science and Art," November, 1872, p. 387), and its general operation may be explained as follows:Let S of the diagram be the source of a sound, and let the circle represent a wave-surface produced by that sound. On this surface all the molecules of air have, at the same instant, the same direction and the same velocity of vibratory motion. If we can accurately determine two points, R and R', on this wave-surface, and this wave-surface be a spherical one, that is, be not deformed, then a perpendicular, S, erected to the center of a chord drawn between these two points, will, when produced, pass through the source, S. The method consists in determining these two points on a sonorous wave-surface, as follows:
While this contrivance may not yet be entirely practicable, its use, as detailed, makes the fact evident that some apparatus can be arranged by which the aberration in the audition of the mariner may be so corrected that he can locate the source of the sound which is made to assure his safety, but which, misheard, may, as in the case of the Edam and Lepanto, insure his destruction.
It seems evident from President Morton's statements that if the fog-signals of the maritime world, or even of one country, or even those located in the approaches to one of our great harbors, were tuned to one note, and if the ships frequenting those waters were fitted with topophones, or some similar instrument, arranged so as to be in unison with the fog-signals, that aberrations in audition, at least as to direction, might be corrected, so as to determine the location of sound to within at least one compass-point.
Since the development of the topophone a number of other instruments have been invented for determining for the mariner the direction of sound made to warn him from danger. For some time some of our best ocean-steamers have been supplied with an instrument giving sounds of wonderful pitch and intensity, called the siren. It 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. This instrument is now used as a fog-signal by most maritime nations, they having frankly copied from, and, in some instances, obtained it through the United States Lighthouse Establishment; and it has been recently adapted to the use of ocean-steamers. But, to make it thoroughly useful, M. Edme Genglaire, a student of the Naval School of Medicine at Toulon, has combined with the siren what purports to be the leading idea of the topophone by fixing an invariable standard for comparison. The siren being in communication with the boiler, the current of steam can be governed by an ordinary valve. The sounds produced vary in pitch and intensity in proportion to the quantity of steam emitted, so that sounds of any given pitch can be obtained. A set of resonators completes the apparatus.
It is well known that two identical resonators vibrate together for the same sound and for that only. Starting with this principle, in two similar frames containing several resonators, the corresponding resonators will vibrate or sound only when the note corresponding to them is produced. The siren will produce these sounds causing vibrations in the resonators, and two distant ships, or a shore-station and a ship, or two land-stations, supplied with sirens of a similar model and identical frames of resonators, could most conveniently communicate. For this end each resonator should have attached to it an invariable signification, the same for all the frames.
All the naval and commercial vessels possessing sirens and a frame carrying the same number of resonators, each marked with a number having its signification, might be prepared to communicate with each other or with the shore.
This is the practical way of carrying the theory out as proposed by M. Genglaire:
In front of each resonator will be placed two metallic reeds, one rigid, the other thin and producing extended oscillations with the least effort. Each of these pieces of steel communicates with one pole or battery by means of the circuit wire. When the resonator vibrates, the thin reed oscillates, touches the other bar, and the two poles of the battery being connected, an electric bell rings, thus giving a signal, so that the call, whether from ship or shore, can be recognized, while the bell of the signaling-station, by its sounds, shows that the desired vibration or note has been produced. This account of Genglaire's siren is condensed from the account published in "Électricité."
Colladon made a series of experiments at Lake Geneva in 1836 to determine the velocity of sound in water. He had a bell weighing about one hundred and fifty pounds suspended some five feet under water from the side of a boat, and struck by a hammer attached to the end of a lever. Stationed in another boat he listened for the bell-sounds, propagated beneath the surface, which were conveyed from the water by a cylindrical tube of tin some nine feet long and six inches in diameter, one end of which terminated in an orifice for insertion in the ear, and the other was spread out somewhat in the form of a spoon, its opening being closed by a flat, elliptic plate of tin, about two square feet in area. By attaching a suitable weight to the lower end of the tube it was easily retained in a vertical position with about four fifths of its length submerged, its flat plate being turned toward the boat carrying the bell. With this simple apparatus, Colladon was able to hear with perfect distinctness the blows of the hammer on the bell across the widest part of Lake Geneva, when the calculated distance between the two boats was not less than eight miles.
The sounds heard by Colladon appeared as if they had been caused "by some metallic body striking the bottom of the tube," and they were "as distinct and brief at 13,000 metres as at 100 metres from the bell." One set of observations were made during a strong wind: "The lake, which was at first calm, became violently agitated, and it was necessary to keep the boat in position by means of several anchors; yet, in spite of the noise of the waves which struck the tube, he took other observations with the same accuracy as when the air and water were still. And he states,"I am convinced that by employing a bigger bell, and improving or enlarging the hearing apparatus, easy communication could be effected under the water of a lake or of the sea up to fifteen or twenty leagues."
In February, 1883, Prof. Lucien I. Blake, now of the University of Kansas, but then in Berlin, while investigating the experiments of Colladon and also of Sturm, as to the velocity of sound through the waters of Lake Geneva, thought of making a practical use of water as a means of communication between vessels at sea. He then devised several methods, assisted by Dr. König, of the Physical Laboratory at the Royal University, which he tried on his return to this country, and he has been experimenting in that direction from time to time since that date, as opportunity served.
His plan, in brief, was as follows: A sound-producing apparatus was to be attached to each vessel, and to be worked under the surface of the water. In times of fog or at night a code of signals would be produced by it which would be transmitted in all directions through the water, with a velocity four to five times that in the air. Each vessel, in addition to the sound-producing apparatus, would be provided with a sound-receiving apparatus, which would take up out of the water the signals arriving from neighboring vessels. As boys in swimming communicate the sound of the striking of stones together under water, so is it possible to send musical tones from one ship to another.
For steamships the sound-producing apparatus was designed to be a steam fog-horn or whistle, specially constructed to sound under water, and to be heard at least from six to eight miles. From the nature of its tone it would be easily distinguishable from other sounds always more or less present under water, such as from breakers, waves, etc. With such whistles a Morse alphabet of long and short blasts and pauses was to provide a means of extended communication, while a simple universal code would indicate a ship's course. Since ignorance of the very presence of a ship, rather than incorrect estimates of her course, has been the principal cause of ocean collisions, the simple hearing of the sound would prove a most excellent general safeguard. Bell-buoys were to have a second bell added under water, while lightships, lighthouses, and any headlands might also be provided with submerged bells which could be rung from the shore, when necessary. Sailing-craft, both large and small, would have bells; and, since an ordinary locomotive-bell can be heard, according to experiments, at least two miles under water, these simple means would seem to afford sufficient limits for protection for such vessels.
As to the receiving apparatus, with which each vessel was to be provided: The original plan of 1883, and which has not been changed, was to employ some form of telephone acting as a transmitter under water, and connected with a receiver within the vessel. The surface of the transmitter exposed to the water, and which must receive the sound-waves, should be protected against ice, barnacles, heavy waves, etc. One design was: One or more vertical pipes in different parts of a ship were to extend from the vessel's interior through the hull, near the keel, and be open to the free admission of water at their lower ends; their upper ends were to extend within the vessel a little way above the keel, and were to be plugged, so that the water could not overflow into the vessel. These pipes would then provide columns of water always still, and would communicate directly with the water outside. Sound would then enter and pass up these pipes, and would encounter microphonic transmitters placed suitably in them. Wires from the transmitters would run to a small room secluded where convenient in the ship, away from disturbing noises, and here telephone receivers would be placed, and observers stationed here in night or fog.
For small craft, it was found that a pipe shaped much like a powder-horn, with a thin, flexible membrane stretched tightly across its broad end, made a successful receiver. With the small end made to fit the ear, and the diaphragm end only a few inches below the water, the sound of a hand-bell has been received nearly a mile distant. Colladon and Sturm used a somewhat similar receiver, and heard a heavy bell ten miles away.
It was necessary to devise a better form of receiving apparatus. The Bell receiver and the Blake transmitter will not work under water. The first success was obtained by a form of transmitter resembling the Ader.
With this Prof. Blake transmitted and received signals between boats half a mile apart on the Taunton River in 1883. The transmitter was weighted to float at different depths, but in all positions as regards the approaching sound-waves it received equally well. Up to half a mile the signals from an ordinary dinner-bell were distinctly heard. These experiments seemed to indicate that a transmitter dependent upon a variable contact might yet be made which would work with satisfaction. This line was consequently followed up, and apparatus was devised by which signals were transmitted between boats a mile distant off Stone Bridge, near Newport, R. I., in the same summer of 1883 through a rough sea and in a dense fog. Various forms of microphonic transmitters were constructed, and experiments on Long Island Sound and on the Wabash River at Terre Haute, Ind., were conducted as opportunity permitted. One form of transmitter which worked fairly well consists merely of a diaphragm having within itself the elements of a microphone. It is placed in simple voltaic circuit with a Bell receiver. This diaphragm is made of hard carbon in granules about the size of smallest shot. A paste is made of these with rubber cement, and this in a mold and die under heat and pressure becomes a hard, thin, elastic disk. This diaphragm takes up the sound vibrations quite well out of the water. The action is similar to that of a multiple contact transmitter. On the river, however, through a long distance these did not seem sufficiently satisfactory. This difference in action between a long and short distance led to the thought that, as the advancing front of the sound-wave is an arc, approaching in curvature nearer and nearer the tangent to its circle, a large diaphragm would receive more sonorous energy and thus probably prove more effective. This is the point to which the experiments have now been carried, and the next trials will be with a diaphragm eighteen inches square. In October, 1885, signals were transmitted and received one and a half mile on the Wabash River from a locomotive-bell around three or four windings of the river, so that the operators were out of each other's sight and the sound could not be heard through the air, yet could be with fair distinctness through the telephone.
It is to be hoped that Prof. Blake may find opportunity to continue his experiments, as he seems to be on the verge of producing a practical and accurate instrument of value to mariners.
Methods of using the Morse code of dots and dashes, as represented by long and short sounds of a fog-whistle or other similar contrivance, have been made public. The best one I have met is that of Mr. Frank Purinton, of Providence, R. I., and it is one of the best because it is the simplest. The idea is that, when two ships meet in fog and make known their proximity to each other by their fog-signals, each shall indicate to the other the way she is steering by the length and the intermission of the sounds made by her fog-signal. The following is the code in part, the long blast being represented by the [—] dash, the short one by the [•] dot:
|Southeast||•——||One dot and two dashes,|
|Northwest||—••||One dash and two dots.|
The thirty-two points of the compass are represented by variations of the collocations of dots and dashes on the chart, and with long and short sounds with intervals, in practice. These signals can be given by the ordinary steam-whistle or by automatic apparatus already invented and in use. Mr. Purinton claims that his system will, if followed, prevent collisions. The four cardinal points of the compass are so represented that opposite courses have opposite signals. One long sound means north; a short one, south. Two long sounds mean east, and two short ones mean west. Other points of the compass are indicated by the synthesis or natural combination made by adding the necessary cardinal signals for the intermediate points or courses.
Another device, which may be called the echo-maker, that of Mr. De la Torre, has been examined by a board of naval officers, of which Commander Bainbridge Hoff, United States Navy, was the head, and report was made to the Navy Department of a somewhat favorable nature. It may consist of a flaring funnel screwed on the muzzle of a rifle. It is operated by firing the rifle in the direction of the supposed obstacle, such as a rock, an iceberg, another ship, or a cliff. If the obstacle is there, the beam of sound projected through the funnel strikes the obstacle and rebounds; and as the echo is more or less perfect in proportion as the obstacle is more or less parallel to the ship from which the gun is fired, and as it is near or remote, the position of the obstacle may thus be inferred. The board reported that De la Torre's method was firing a blank cartridge from a rifle in the presence of objects as small as a spar-buoy and as large as a fort, and catching the return sound or echo. He claims that a sharp sound projected at or nearly at an object, and only when so directed, will in every case return some of the sound sent, so that theoretically there will always be an echo, and the difference in the time between the sound sent and the echo will indicate the remoteness of the object. The board found that a return-sound could be heard from the side of a fort a half-mile off, from passing steamers a quarter-mile off if broadside-to, from bluffs and sails of vessels about the same distance, and from spar-buoys two hundred yards away.
The board further states that the sound from the different kinds of masses is different in most cases, and that the ear could be educated to detect quite a range of different objects, as the echo from a sail was different from the echo from a buoy or a bluff. If two objects were near the line of projection at different distances, an echo would be received from each. The horizontal limit of the return of sound seemed to be about two points on each side of the axis of projection.
If Mr. De la Torre should see fit to construct his instrument for hearing feeble echoes, the board indicated that it would recommend that it be fitted soon to some vessel of the North Atlantic Station, and that further and, if possible, exhaustive experiments ought to be made to practically determine the use of the echo as a means to discover obstacles to navigation. It was also stated that steam-whistles could be heard much farther than the echo; but it was said that where the obstacle could not make the sound, as in the case of an iceberg, the echo would be of the greatest use, and experiments looking to its utilization are demanded by the conditions of navigation in time of fog.
Steamers are constantly running among the islands on the coast of Maine during the summer. This is the season of thick and persistent fog. When pilots can hardly see the length of their vessels, they keep up a constant noise with their fog-signals. The open sea gives back no sound. But the near or remote vicinity of cliffs, bluffs, or even high shores, is indicated by the strength of the echo received back from them. In fact, running by echo is recognized as one of the necessities of the navigation of those waters.
This method is also used to some extent by steamers on the great rivers. And it is practiced on the Great Lakes to some extent, notably at a certain bluff jutting out into Lake Superior. Passing steamers, knowing themselves to be in the vicinity, when befogged, feel out these bluffs by sounding their fog-signals until they get back an echo; then they use the bluffs as a new point of departure.
In this connection I may say that in the summer of 1886 I experimented in making echoes while on a lighthouse steamer on Long Island Sound, and found I could get a good echo by sounding the whistle of my steamer when passing a sailing-vessel, preferably a schooner, on a parallel course. Wave-sounds striking her sails at right angles to her course, gave a good echo at five hundred yards or less, and the sound of the echo was more or less good within that distance, in proportion to the angle made by the courses of the two vessels when their courses were not parallel. When off Block Island cliffs, which overhang somewhat, I got a good echo when about a mile distant. Hence I infer that the position of suspected dangers of certain kinds can be determined by the production of echoes under specified circumstances.
Recent papers state that Mr. H. B. Cox, an electrician whose laboratory is at Fernbank, some ten miles from Cincinnati, has invented a trumpet to be used for telephoning at sea, on which he has been at work for some months. The invention is the outgrowth of his discovery of the great distance an echoed or reverberated sound will carry, and the discovery that speaking-trumpets, if made to give the same fundamental note, would vibrate and produce the phenomenon known in acoustics as "sympathy."
With this trumpet conversation in an ordinary tone of voice was carried on between parties four and a quarter miles apart. People a mile away, conversing in an ordinary tone, could be distinctly heard, and in two instances they were told the nature of their conversation, and admitted that such had taken place. The whistle of a train was traced beyond Fernbank to Lawrenceburg, Ind. It was found that the instrument has a well-defined range of twenty-six miles; that is, a loud sound like a locomotive-whistle, or the rumbling of a train, can be distinctly heard at a distance of thirteen miles in every direction. Conversation was readily carried on between two gentlemen on high hills on opposite sides of the Ohio River distant about four and a half miles apart. Tests made on the water, of various kinds, showed that the trumpet was even more available than on land.
It is generally understood that Mr. Edison, who has invented so many good things, is now at work, and has made promising progress on the production of what may be called a water-telephone, by which he proposes to enable ships within hearing distance to communicate without wires, but still by electricity, sent and received through the water. He is said to have signaled through a mile of the Caloosahatchie River, in Florida, during his experiments made last winter.
The object of this paper is to call attention to the practical impossibility of the mariner determining, by his unassisted ears, in a fog or in darkness, the position of another ship from the noise she makes, and the necessity that he should use some of the appliances named, or better ones as they appear, to assist his ears, and thus to prevent the collisions which are now so frequent and so disastrous. The Celtic and Britannic steamers would not have run into each other had such appliances been used; nor would the steamer the City of Brussels have been run down in the English Channel by the steamer Kirby Hall had they been thus supplied, to say nothing of the steamer Oregon recently sunk off Fire Island, and other like cases within easy recollection. These vessels carried no such appliances.
It is desirable that public opinion should be brought to bear on this subject with such force that ships shall be required to carry some appliance, so that an error of five points in fixing a ship's position will no longer be possible, or, if possible, will be held to be criminal negligence.
It is also desirable that public opinion should be brought to bear on this subject with so much force that ships will be required to carry and use proper appliances for ascertaining the position and course of ships within ear-shot, as they are now required to carry lights for a like purpose.
And why should not the Federal Government take some steps in this direction, that the dread all now feel of collision at sea, in the fog or the darkness, may in some measure be eliminated?
Since the foregoing was in the hands of the editors. Senator Frye introduced into the Senate Bill No. 1851, "to provide for an international conference for securing greater safety for life and property at sea." The President, under this bill, is to invite each maritime nation to send delegates to a maritime conference, to meet at Washington in October next, and to appoint five delegates to represent the United States.
One of the duties prescribed for this conference is "to adopt a uniform system of marine signals or other means of plainly indicating the direction in which vessels are moving in fog, mist, falling snow, and thick weather, and at night."
This bill was referred to the Committee on Foreign Relations, whence it was reported back on February 15th with, certain helpful amendments. On February 23d it was taken up, when Senator Frye said: "That is a public bill of very great importance. ... It is a bill recommended by the President and Secretary of State, and indorsed by nearly all the boards of trade, chambers of commerce, and maritime associations." The bill was then passed and sent to the House of Representatives, when it was referred to its Committee on Foreign Affairs.
- See "Federal Reporter," October 28, 1884, p. 651,
- "Memoirs of the Institute of France," vol. v, 1838, pp. 329-399; Sir John Herschel, "Sound," sections 94, 95; "Journal of Science," vol. i, 1828, pp. 480, 481; "Edinburgh New Philosophical Journal," vol. v, 1828, pp. 91-94.