Part 2
_Messrs. Cecil and Leonard Wray’s Telephone._--This system, represented in figs. 2 and 3, is simply an improvement on that of M. Reiss, with the object of intensifying the effects produced. The sender is provided with two membranes, instead of one; and its receiver, instead of being formed of a single iron wire covered with a magnetising coil, is composed of two distinct coils H, H′ (fig. 2), placed in the same straight line, and within which are two iron rods. These rods are fastened by one of their ends to two copper disks A, B; these disks are maintained in a fixed position by screws I, I′, and the two other extremities of the rods, between the coils, are opposite each other, not touching, but divided by a very small interval. The instrument is set upon a sounding-box, in which there is a hole T in the space corresponding to the interval between the coils: these coils communicate with four terminals, which are connected with the electric current in such a way that the adjacent poles of the two rods are of opposite polarity, thus forming a single magnet, divided in the centre. It seems that by this arrangement the sound produced becomes much more distinct.
[Illustration: FIG. 2.]
[Illustration: FIG. 3.]
The form of the sender also is somewhat different from the one we have previously described: the upper part, instead of being horizontal, is rather inclined, as it appears in fig. 3, and the opening E through which the sound has to communicate with the vibrating membrane, occupies a great part of the upper surface of the box, which consequently appears to be somewhat oblique. The second membrane G, which is of caoutchouc, forms a sort of partition which divides the box in two, starting from the upper end of the opening: the inventor states that this will protect the outer membrane D from the breath and other injurious effects, while increasing the force of the vibrations produced on the first membrane, as in a drum. The contact-breaker itself also differs from the one in M. Reiss’s instrument. The platinum disk _b_ is only placed in circuit by means of two slender wires of platinum or steel, which are immersed in two small cups, filled with mercury, and connected with the circuit. In this way, the movements of the membrane D are free, and its vibration is rendered more easy.
The circuit is also broken by a little platinum point resting on a lever with a spring-joint, K H, which is above the disk: one end of the lever, which is fixed below a kind of Morse key M I, makes it possible to close the circuit with the hand, so as to give the signal for setting the apparatus to work.
_Electric Harmonica._--Long before M. Reiss’s invention, and consequently still longer before that of Mr. Elisha Gray, I mentioned a sort of electric harmonica, and described it as follows in the first edition of my ‘Exposé des applications de l’Electricité,’ published in 1853:--
‘The power possessed by electricity to set metallic plates in motion and cause their vibration has been used for the production of distinct sounds, which can be combined and harmonised; but in addition to this purely physical application, electro-magnetism has come to the aid of certain instruments, such as pianos, organs, &c., rendering them capable of being played at a distance. So that this extraordinary force may be turned to account in arts which are apparently the least susceptible of any application of electricity.
‘We have already spoken of M. de la Rive’s contact-breaker. It is, as we know, an iron disk, soldered to a steel spring, and maintained in a fixed position opposite to an electro-magnet by another spring in connection with one branch of the current. As the other branch, after passing into the wire of the electro-magnet, terminates in the iron disk itself, the electro-magnet is only active at the moment when the disk touches the terminal spring; at the moment of leaving it, the magnetism ceases, and the iron disk returns to its normal position, and then leaves it again. In this way a vibration is produced, rapid in proportion to the small size of the vibrating disk, and to the greatness of the force produced by the approach of the disk to the electro-magnet.
‘In order to increase the acuteness of the sounds, one or other of these expedients must be employed. The simplest way is to use a screw which can be tightened or relaxed at pleasure, and which in this manner removes the vibrating disk to a greater or less distance from the electro-magnet. This is the case in M. Froment’s instrument, and by this means he has obtained sounds of extraordinary acuteness, although not unpleasant to the ear.
‘M. Froment has not applied the apparatus to a musical instrument, but it is evident that it would be easy to do so; it would only be necessary to make the notes of a key-board act on metallic levers, of a length corresponding to the position required by the disk for the vibration of different tones. These different levers, resting on the disk, would act as a point of contact, but the point would vary in position, according to the touch.
‘If the current were constant, such an instrument would certainly have many advantages over the pipe instruments which are in use, since the vibration might be prolonged at will in the case of each note, and the sounds would be softer; unfortunately the irregular action of the battery makes it difficult in practice. These kinds of instruments are therefore only used as a means of regulating by ear the force of the battery, a much more convenient regulator than the rheometers, since it is possible to estimate by them the variations of the battery during an experiment without any distraction of the mind.’
In 1856 M. Pétrina, of Prague, invented an analogous arrangement, to which he gave the name of electric harmonica, although, strictly speaking, he had not thought of it as a musical instrument. This is what I have said on the subject in vol. iv. of the second edition of my ‘Exposé des applications de l’Electricité,’ published in 1859:--
‘The principle of this instrument is similar to that of Neef’s rheotome, in which the hammer is replaced by slender rods, whose vibrations produce a sound. Four of these rods are placed side by side, and when moved by keys, and arrested by levers, produce combined sounds of which the origin may be easily shown.’
It is true that nothing is said in this passage of the capability possessed by these instruments of being played at a distance; but this idea was quite legitimate, and German periodicals assert that it was accomplished by M. Pétrina even before 1856. It was the result of what I said at the outset: ‘that electro-magnetism may come to the aid of certain instruments, such as pianos, organs, &c., _in order to enable them to be played at a distance_,’ and I also pointed out the expedients employed for the purpose, and even for setting them at work, under the influence of a small musical box. I did not, however, ascribe importance to the matter, and it is only by way of historical illustration that I speak of these systems.
_Telephone by Mr. Elisha Gray, of Chicago._--This system, invented in 1874, is in reality only an instrument of the nature of those which preceded it, but with important modifications, which made it possible to apply it usefully to telegraphy. In an early model, he made use of an induction coil, with two helices, one over the other: the contact-breaker, which was vibrating, was multiple, and so arranged as to produce vibrations numerous enough to emit sounds. These sounds may, as we have seen, be modified by this arrangement, according to the mode in which the instrument is adjusted, and if there are a certain number of such contact-breakers side by side, with vibrating disks so ordered as to produce the different notes of the scale on several octaves, it becomes possible, by a combination of certain notes, to execute on this new kind of instrument a piece of music such as may be produced by an harmonium, an accordion, or any other instrument with blowers. The contact-breakers are set in motion by means of the primary current of the induction coil, as it circulates through one or other of the electro-magnets of these contact-breakers, actuated by the lowering of the notes of a key-board connected with them, and the secondary currents which arise in the coil, in consequence of the interruptions in the primary currents, transmit the corresponding vibrations to a remote receiver. There is an analogy between this instrument and the telephones of which we have already spoken by Reiss and Wray, but the effect is increased by Mr. Gray’s modifications.
We represent in fig. 4 the arrangement of the first system. The vibrators are A and A′, the key-board M and M′, the induction coil B, and the receiver C. This receiver consists, as we see, of a simple electro-magnet N N′: above its poles there is a metal cylindrical case C, of which the bottom is made of iron, to serve as an armature. This box, like a violin, is pierced with two holes in the form S, to serve as a sounding-board; and Mr. Elisha Gray has ascertained that the molecular motion which takes place in the magnetic core and its armature, under the influence of alternate magnetisation and demagnetisation, sufficed to produce vibrations corresponding to the velocity of these alternations, and to emit sounds which became audible when they were magnified by the sounding-board.
[Illustration: FIG. 4.]
It is quite intelligible that the effect obtained in this system might be reproduced, if, instead of contact-breakers or electric rheotomes, mechanical contact-breakers were used at the sending station, so arranged as to furnish the requisite number of breaks in the current which communicates the vibrations of the different notes of the scale. In this way also it would be possible to dispense with the induction coil, by causing the current which has been broken by the mechanical contact-breaker to react upon the receiver. Mr. Elisha Gray has moreover made a different arrangement of this telephonic system, which he has applied to telegraphy for simultaneous electric transmissions, of which we shall speak presently.
If we may believe Mr. Elisha Gray, the vibrations transmitted by the secondary currents would be capable, by the intervention of the human body, of causing the sounds to be reproduced at a distance by conducting disks, which vibrate readily, and are placed on a sounding-box. In this way musical sounds may be evoked from copper cylinders placed upon a table, from a metallic disk fastened to a kind of violin, from a membrane stretched on a drum, or from any other resonant substance, by touching any of these objects with one hand, while holding the end of the line with the other. These sounds, of which the quality must vary with the substance touched, would reproduce the transmitted note with the precise number of vibrations which belong to it.[1]
_Mr. Varley’s Telephone._--This is, strictly speaking, merely a musical telephone of the same kind as that of Mr. Gray, but the arrangement of the receiver is original and interesting. This part of the instrument essentially consists of a drum of large size (three or four feet in diameter), within which is a condenser formed of four sheets of tinfoil, divided by sheets of some insulating material, and with a surface of about half the size of the drum. The plates of the condenser are placed parallel to the membranes of the drum, and very little removed from its surface.
If an electric charge is communicated to one of the series of conducting plates of the condenser, those which correspond to it are attracted, and if they were movable they might communicate to the intervening strata of air a movement which, on reaching the membranes of the drum, might, by a series of charges in rapid succession, cause the membranes to vibrate, and thus produce sounds: these sounds would correspond to the number of charges and discharges which had occurred. Since these charges and discharges are determined by the contact of the two plates of the condenser, at the extremities of the secondary circuit of an induction coil, of which the primary circuit has been duly broken, it becomes evident that, in order to cause the drum to emit any given sound, it will be enough to produce the number of vibrations in the contact-breaker of the induction coil which are required for this sound.
The means employed by Mr. Varley to produce these interruptions are the same which are in use in several electrical instruments, and especially in chronographs--an electro-magnetic tuning-fork, regulated so as to emit the sound required. This tuning-fork may, by acting as contact-breaker, react on the primary current of the induction coil; if the number of the tuning-forks equals that of the musical notes which are to be transmitted, and if the electro-magnets which set them in motion are connected with the key-board of a piano, it would be possible to transmit a melody to a distance by this system, as well as by that of Mr. Elisha Gray.
The peculiarity of this system consists in the reproduction of sounds by the action of a condenser, and we shall presently see that this idea, adopted by Messrs. Pollard and Gamier, led to interesting results.
_Singing Condenser of MM. Pollard and Garnier._--This instrument, which astonishes all who hear it, attracted public attention in London some time ago. It is difficult to say why its fame was not greater, since much attention has been bestowed on less curious instruments. It is a fact that we have been able, thanks to MM. Pollard and Garnier, to hear songs issue from a sort of copy-book, so as to become audible throughout the room. The songs thus reproduced are certainly not always perfectly true; yet when the person who sings into the sender is a musician, and understands how to make use of it, the condenser in question will emit sounds somewhat resembling those of the violoncello or the hautbois.
The singing instrument consists of a condenser K, formed of thirty sheets of paper, laid one over the other, from nine to thirteen centimètres in thickness: between these, twenty-eight sheets of tinfoil, from six to twelve centimètres thick, are intercalated, so joined as to form the two plates of the condenser. For this purpose the pair sheets are joined together at one end of the copy-book, and the odd sheets at the other end. This system is fastened to a stiff _carton_, after taking care to bind it with a strip of paper, and the sheets of tinfoil are joined to the two ends of the condenser by two copper rims D, D, which are provided with terminals for the circuit wire, and in this way the singing instrument is constructed. A somewhat heavy weight, placed upon the condenser to compress the sheets, does not in any way prevent it from working; and this vitiates the theory first put forward to explain its effects, that the sheets were moved by attraction.
[Illustration: FIG. 5.]
The sending instrument consists of a sort of telephone without a handle, E, of which the vibrating disk is formed of a very thin plate of tin. A cylindrical piece of carbon C is fastened to its centre, and is supported by another cylinder of the same material H. This rests on a transverse piece of wood A B, jointed on the side A, on the edge opposite to the box, by means of a regulating screw V. An arched spring R (the end of a watch spring) placed across this piece of wood gives it a certain elasticity beneath the pressure, and this elasticity is necessary in order that the instrument may act properly, and it thus becomes a sort of microphone with a diaphragm.
The tin plate is put into communication with one pole of a battery P, of six Leclanché cells, and the lower carbon cylinder H corresponds to the primary helix of an induction coil M, previously connected with the second pole of the battery: Finally, the two extremities of the secondary helix of the coil, _a_ and _b_, are in immediate connection with the two plates D, D, of the condenser.
This secondary helix should consist of twenty strands of wire No. 32, covered with silk, and the primary helix is made of five strands of wire No. 16. The length of the coil should not exceed seven centimètres and the diameter of the core of fine iron wire ought to be about one centimètre.
In order to produce song on the condenser, the sender must be so regulated that the two carbons C and H do not touch each other in their normal condition, but they should be so close that in singing the vibrations of the disk L L may effect the needful contacts. The adjustment can be easily made by the touch, and by uttering the same note until it is repeated by the condenser. If three notes, given in succession, are faithfully reproduced, the instrument may be assumed to be properly regulated, and, in order to make it work, it is enough to apply the mouth to the mouthpiece as it is applied to a reed pipe.
In order to obtain a satisfactory result, the disk of the instrument must be heard to vibrate, as in a _flûte à l’oignon_. Instead of carbons, contacts of platinum may be used; but when arranged as we have described, the instrument may be employed for several purposes, as we shall see presently. This instrument is made by MM. Chardin and Prayer. M. Janssens has made the system more portable by fastening the sender, represented in fig. 5, to a handle in which the induction coil is placed: the instrument then resembles an ordinary telephone, and the vibration of the diaphragm is made more easy by piercing two holes in it. On the side of the sending-box, above and below the diaphragm, there are binding screws in connection with the end of the handle, since the instrument may be used as an ordinary telephonic sender, and even as a telephonic receiver.
SPEAKING TELEPHONES.
We have seen that the telephones just described can only transmit musical sounds, since they can merely repeat simple vibrations, in greater or less number, it is true, but not in simultaneous combinations like those which reproduce articulate sounds. Up to the time of Mr. Bell’s invention, the transmission of speech could only take place with the aid of acoustic tubes, or of the string telephones of which we have spoken. Although these instruments have no connection with the object of our study in this work, we have thought it necessary to say a few words about them, since they may sometimes be combined with electric telephones, and also represent the first stage of the invention.
_String Telephones._--These instruments, which have flooded the cities of Europe for several years, since the date of the invention was 1867, are interesting in themselves, and we are surprised that they have not hitherto taken a place in the collections of physical science. They are made of two metal or cardboard tubes, in the form of a cylindrical cone: one end is closed by a tightly stretched membrane of parchment, in the centre of which the cord or string intended to connect the two cylinders is fastened by a knot. When two such tubes are connected in this way, and the cord is tightly stretched, as in fig. 6, it is only necessary to apply one tube to the ear, while another speaks into the opening of the other tube: the words spoken by the latter are instantly transmitted, and it is even possible to converse in quite an undertone. Under these conditions the vibrations of the membrane affected by the voice are mechanically transmitted to the other membrane by the string, which, as Robert Hooke declared in 1667, is a better transmitter of sound than the air. In this way it is possible to communicate at a distance of 170 yards, and the size and nature of the cord have some influence. The sellers of these instruments say that the best results are obtained from silken cords, and the worst from those made of hemp. Cords of plaited cotton are usually employed for the sake of cheapness.
[Illustration: FIG. 6.]
In some patterns, the tubes are so arranged as to present, between the membrane and the mouth, a diaphragm pierced with a hole, and the instrument somewhat resembles a bell with its base bored and closed again a little above the parchment membrane; but I have not observed that this pattern is decidedly superior to the others.
It has also been asserted that horn-shaped tubes of nickel silver are to be preferred, of which I am equally doubtful. At any rate, these instruments have produced unexpected results; and although their practical use is very limited, they are interesting from a scientific point of view, and are instructive toys for children.
Mr. Millar, of Glasgow, declares that the effect produced by these telephones depends very much on the nature of the string, the way in which it is attached, and the way in which the membrane is fastened to the mouthpiece.
_Improvements made in the String Telephone._--The amazing effects of the Bell telephones have lately brought the string telephones, which were only regarded as children’s toys, again into fashion. Since they have made it possible to transmit to several persons the words reproduced by an electric telephone, means have been sought for combining them usefully with the latter, and the best mode of making them speak on a string presenting several angles has been sought for: it has been shown that, under the usual conditions, these instruments only speak distinctly when the string is stretched in a right line. To solve this problem, it occurred to M. A. Bréguet to make use of a sort of tambourine for the supports, with the string passed through their centre; the sound conveyed by that part of the string which is in connection with the speaking-horn causes the membrane of the tambourine to vibrate, which again communicates the vibration to the next portion of string. In this way the angles may be multiplied at will, and the string may be supported throughout the length compatible with this kind of telephone, which does not exceed 112 yards.
M. A. Bréguet has also invented a system of relays to accomplish the same object. He makes the strings terminate in two membranes which close the two openings of a brass cylinder. The sounds reproduced on one of these membranes react upon the other, which vibrates under its influence, as if it were affected by the voice. The cylinder then acts as an ordinary acoustic tube, and its form may be varied at pleasure.
M. A. Badet, on February 1, 1878, succeeded in making string telephones in an analogous way, and he used parchment stretched upon frames which acted as resonant boards. The string was fixed in the centre of the membrane, and made with it the angle desired.