Part 20

He observes that a singular fact has been discovered by several persons, who have ascertained that not merely non-magnetic and non-conducting bodies can be substituted for the diaphragms of receiving telephones, but that they will act without a diaphragm at all. In this case it is evident that we have to do with the sounds discovered by Page, and that they are produced by the magnet itself, in which each molecular movement constitutes the source of the sound produced. This sound becomes articulate as soon as its increase and decrease can follow the increasing or decreasing action of the voice which produces it at the sending station. It is certain that when the transmitted currents are due to the action of the Bell diaphragm, the sounds due to the Page effects ought to correspond with those which would be given by iron diaphragms adapted to the receiving instruments; so that, when a telephone has an iron diaphragm, there are in fact two voices, that of the diaphragm, which is strong, and that of the magnet, which is weak. When a disk of wood is substituted for one of iron, it acts as a sounding board for the Page effect, and when the disk is of metal, induction is developed by the magnetic modifications, and tends to produce vibration, thus developing a third source of sound, which may be called the Ampère effect. Finally, a fourth source of sound may result from the induced effects produced in the wire itself in consequence of changes in the intensity of current. These sounds, first observed by M. de la Rive, have since been studied by Mr. Fergusson of Edinburgh (vide ‘Telegraphic Journal’ of November 1, 1878).

Mr. Fleeming Jenkin’s opinion only differs from mine in his ascribing the energy of sound acquired by a telephone with an iron diaphragm to the preponderance of sounds in the latter, whereas I consider it to be chiefly due to the increase of energy in the whole magnetic system produced by the reaction of the two magnetic parts on each other. If the two effects could be taken singly, it is probable that the sounds produced by each of them separately would be similar, since in magnetic effects the reaction and action are equal. But as they are combined, it becomes difficult to assign to each the share which belongs to it in the general effect observed. Besides, it is quite possible that the sounds of the diaphragm may appear to be stronger and more distinct because it is nearer to the ear than the magnet, and because the effects of magnetisation and demagnetisation are then more easily produced in consequence of the mass of the magnetic body being smaller.

Mr. Fleeming Jenkin goes on to say that the question of the displacement of surface in the diaphragm and magnet is very complex, but that he thinks it impossible to deny the existence of such displacement, since the air which acts as the vehicle of sound between the ear and the source of sound is placed in vibration; yet this displacement maybe effected quite otherwise than by flexion. Suppose that the magnetic molecules of these bodies are drawn together by magnetisation, which tends to diminish the intermolecular space which separates them, the points of surface of the substance corresponding to these intervals will be elevated in a manner equivalent to a displacement of surface, and the effect of this will be the same as a flexion movement. At the moment of demagnetisation a depression instead of an elevation will take place, and the vibratory movements will thus be produced without any electro-magnetic attraction, and it is precisely these vibrations which Mr. Fleeming Jenkin terms molecular vibrations. He evidently does not mean that such attractions cannot take place: they may react, together with the molecular vibrations, when the electric force is capable of producing them. He adds that the reproduction of sounds by a condenser, by simple coils, and by a carbon microphone, has convinced him that the action just analysed requires generalisation.

We have recently seen an article by Mr. Hughes in the ‘Telegraphic Journal,’ Nov. 15, 1878, in which, to our surprise, he not only opposes all the theories he has hitherto held, but cites experiments which are quite inconclusive, since they were performed under conditions in which electro-magnetic effects must necessarily be displayed. He made use of voltaic currents produced by a battery of three Daniell cells. In order to estimate the transverse effects resulting in such a case from attraction, the experiments he mentions are wholly unnecessary: they may be felt with the hand. On the other hand, he has evidently forgotten that the currents employed in a Bell telephone have no influence on a very sensitive galvanometer.

_M. Pollard’s Microphone._--This microphone, which has been arranged in several ways, essentially consists of a carbon rod kept in a horizontal position by a wire, and resting on two other vertical carbons. The upright of the arm which holds the wire can revolve together with this arm, and is thus able to regulate the pressure of the horizontal carbon on the two vertical carbons. It appears that this instrument is extremely sensitive, and that the regulation effected on the two contacts is better than when it is effected on one only. It is fair to add that M. Voisin previously sent me the sketch of a somewhat similar arrangement.

M. Dutertre has also made use of such an arrangement in what he calls the Dolmen microphone. Three pieces of coke in the form of a dolmen, that is, two uprights, supporting a third and horizontal carbon, are placed in circuit. M. Gouault has informed me that speech was well transmitted by this instrument, and it is, like that of Mr. Blyth, which succeeded it, of wonderful simplicity.

This microphone, as well as one composed of two pieces of lead-pencil placed in a watch-case, and connected by a piece of money, were exhibited to the Industrial Society at Rouen, February 1, 1878, of which an account was published in the Bulletin of that society.

_M. Ader’s Electrophone._--M. Ader has recently constructed a remarkable telephonic instrument, which reproduces speech and song in a quite exceptional and simple way. It consists of a drum 15 centimètres in diameter, covered with parchment at one end only. Six small tin armatures, one centimètre in length and two millimètres in width, are fixed in the centre of the parchment in a circle six centimètres in diameter. Six microscopic electro-magnets, whose distance from the armatures can be regulated by a screw, are placed opposite the armatures within a wooden circle. The magnets are horseshoe, with branches 12 millimètres long and 4 millimètres in diameter, including the coils, and the magnetic core is 1½ millimètre thick. They are all in connection, and act simultaneously under the sole influence of the battery current. The sender is the same as that of M. Ader described before. With this instrument speech may be heard at a distance of six or seven yards, and songs are much more distinctly heard than in the singing condenser. Owing to the simplicity of the arrangement, the instrument is not costly.

The extraordinary effects of this telephone are due to the small size of the electro-magnets, which, as we believe, produce much more rapid magnetic effects than those of larger size. M. Ader has also made a small ordinary telephone based on this principle, of which the sounds are much stronger than in others.

_Modification of Bell Telephone._--Mr. Gower has recently made a new system of telephone without a battery, which not only reproduces speech loudly enough to be heard at the distance of eight or nine yards from the instrument, but will also transmit it when the speaker is at a moderate distance from the sending instrument. In this latter case, indeed, the receiving telephone must be brought close to the ear. Although this double problem had already been solved by the use of telephones with microphonic senders, the results furnished by the instruments in question are still more curious, since they are obtained without batteries, and are even more distinct.

In this new system, which is only an improvement on Bell’s square model, the horseshoe magnet is of a peculiar form, which renders it more powerful. It is formed of a kind of half-circle of magnetised steel, with its two ends turned back, so as to form a diameter of the circle, only this diameter is divided in the centre: so that the two poles of the magnet are placed one before the other, as in Faraday’s electro-magnet. The poles are tipped with iron, terminating in front in two thin iron plates, on which are placed the electro-magnetic coils, which are oblong, and constitute the magnetic core. The diaphragm, thicker than the ordinary diaphragms, is of tin, and is fixed firmly to the edges of the circular box which encloses the whole, and which forms a kind of sounding-box. The box is made of copper, and the diaphragm is so firmly fastened to it as to become homogeneous with it, and to give out a sound when the box is touched, which is not the case in ordinary telephones. This is one of the conditions which make the instrument a better conductor of sound. The magnet is also much more powerful. It is magnetised by a current from a powerful Gramme machine, which acts upon it for almost twenty minutes. The instrument has, strictly speaking, no mouthpiece: the lid of the box which supports the diaphragm, and is separated from it by a space of two millimètres, has merely a hole bored in it above the centre of the diaphragm, and into this hole either a tin trumpet, 50 centimètres in length, is screwed, when the instrument is required to reproduce or transmit speech to a distance, or an acoustic tube when it is to be used like an ordinary telephone. The remarkable part of the system is that the instrument can itself give a very loud call by only breathing into it instead of speaking.

For this purpose a small oblong opening is made in the diaphragm at a half diameter from its centre, and behind this the reed of an harmonium is applied to a square copper plate fixed on the diaphragm itself. On using the bellows the expelled air passes through this little hole, and, on reaching the reed, sets it in vibration, and produces a sound of which the acuteness depends on the conditions of the vibrating plate. This addition to the diaphragm in no way alters its properties in the reproduction of speech, so that, after using the bellows, conversation may begin, and the receiving telephone repeats what is said after emitting a sound somewhat resembling the note of a bugle. The instrument is then provided with the speaking tube of which we have spoken.

Nothing can be more remarkable than this power of listening to conversation while seated in an armchair six or seven yards from the instrument, nor is it necessary to move in order to reply. The correspondent, indeed, must be close to the acoustic tube in order to speak and listen, and he must speak rather loud in order to be heard at any distance from the other station. But the listener receives the sounds so amplified that it might be supposed that a giant was speaking, and conversation held in a low tone may even be distinguished. These results are really extraordinary, and even to those familiar with such effects this incessant progress is surprising.

These results may be ascribed to the following causes:--

1. First, that the conditions of the magnet are better than those of ordinary instruments.

2. That the diaphragm is also thicker, larger, and better stretched.

3. That the box is of metal, and calculated to act as a sounding-box.

4. The speaking trumpet magnifies the sounds.

5. The acoustic tubes concentrate the sound waves on the centre of the diaphragm.

_Note on some fresh Experiments with Telephones without any Diaphragm._

In a paper published March 4, 1878, I made some suggestions on the theory of the sounds produced in the telephone, and on the contradictory assertions of physicists as to the transmission of speech by ordinary telephones when devoid of diaphragm. These remarks induced M. Ader to undertake some experiments which not only demonstrate the truth of my opinion, but bring to light some fresh facts which may be of great importance to acoustic science.

M. Ader has in fact not only succeeded in making a telephone without a diaphragm speak, but he has made it speak more loudly and with less alteration of the voice than we find to be the case with a small model of the ordinary telephone. No one, therefore, can now maintain that the sounds produced by the magnetic cores are so faint that they cannot be taken into account among the effects produced, and that it is at any rate impossible for them to reproduce articulate sounds.

To obtain this result, M. Ader reduced the size of the magnetic core to that of a simple iron wire, one millimètre in diameter, and he fastened it by one of its ends to a small wooden board. Under these conditions, it was enough to fasten a small helix of fine wire on this iron wire, and to apply the board to the ear in order to hear speech distinctly, with the aid of a microphonic speaker actuated by a voltaic current. But the range of sound was considerably increased if a mass of metal was applied to the free end of the iron wire: in this case it was possible to hear when the wooden board was removed to a distance of ten or fifteen centimètres from the ear.

If the wire is in contact with masses of metal at each end, the effect is further increased; but the two masses must not be in metallic communication with each other, and must be to some extent insulated by a more or less elastic medium. If the metallic masses are soldered to the wire, the effects are still greater.

M. Ader was also able to reproduce speech by using a simple coil without a magnetic core, but in this case the spirals must be open, and not pressed together. If they are steeped in gum, no sound is heard, but speech will become instantly audible if a wire or a magnetised needle is inserted in the coil, or even if a second metallic helix is placed in the circuit: always provided that one of the ends of these magnetic organs rests upon, or is fastened to, the board on which the coil is fixed.

M. Ader has likewise obtained a very distinct reproduction of speech at a distance of two or three yards from the instrument by inserting between the two stretched membranes of two tambourines a bent wire which acts as a spring and passes through an electro-magnetic coil. Under these conditions, magnetisation of the wire in a greater or less degree affects its elasticity and causes vibrations which are magnified by the membranes, and transmitted sounds are reproduced with intensity. Unfortunately articulate speech is less distinct with this system than with the one I described before.

M. Ader has often had occasion to make one curious remark, namely, that the _timbre_ of the voice and its high or low key varies with the degree of tension given to the wire; but if the fundamental note of the wire is deadened by pressing it between the fingers, the sounds reproduced then become dull and monotonous. They are also somewhat fainter.

Signor Carlo Resio has also observed that in a telephone sender the variations of intensity in the current correspond with the vibrations caused by speech, and these are reproduced by corresponding variations in a liquid column, which may thus act as a telephone receiver, and consequently may reproduce speech without any electro-magnetic organ, as in a microphone speaker. Under these conditions, however, a layer of water is inserted between the platinum electrodes and the surrounding air, and consequently this liquid layer must be put in vibration under the influence of varying intensities of current.

Mr. Edison has also now made a practical application of the chemical telephone we have mentioned before. The trials made with it have been very satisfactory, showing that sounds transmitted in this way can be heard in a large room.

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FOOTNOTES

[1] Mr. Gray, in an article inserted in the _Telegrapher_ of October 7, 1876, enters into full details of this mode of transmitting sounds by the tissues of the human body, and he gives the following as the conditions in which it must be placed to obtain a favourable result: 1. The electricity must be of a high tension, in order to have an effect perceptible to the ear.

2. The substance employed to touch the metallic plate must be soft, flexible, and a good conductor, up to the point of contact: it must then interpose a slight resistance, neither too great nor too small.

3. The disk and the hand, or any other tissue, must not only be in contact, but the contact must result from rubbing or gliding over the surface.

4. The parts in contact must be dry, so as to maintain the required degree of resistance.

[2] He cites the following names in his account of electric telephony:--Page, Marrian, Beatson, Gassiot, De la Rive, Matteucci, Guillemin, Wertheim, Wartmann, Janniar, Joule, Laborde, Legat, Reiss, Poggendorf, Du Moncel, Delezenne, Gore, &c. Vide Mr. Bell’s paper, in the _Journal of the Society of Telegraphic Engineers_ in London, vol. vi. pp. 390, 391.

[3] This statement is disputed by Mr. Elisha Gray, owing, as we shall see, to a misunderstanding as to the word _undulatory_ current.

[4] _Elisha Gray._ Eng. Pat. Spec. No. 2646, Aug. 1874.

[5] This property has long been known, but not applied. In 1856, in the second edition of my _Exposé des applications d’Electricité_, I pointed them out in speaking of the contact-breakers. I also spoke of them in a paper on electro-magnets (published in the _Annales télégraphiques_, 1865), and in several articles laid before the _Académie des Sciences_ in 1872 and 1875 on the conductivity of filings and conducting powders. M. Clérac, in 1865, also used them to obtain variable resistances.

[6] In 1865 I was able to verify this observation when tightening the spirals of an electro-magnet on a naked wire. The greater the number of spirals under pressure, the more definite were the differences of resistance in the magnetising helix.

[7] M. Hellesen communicated the plan of his instrument to me on May 3, 1878, and his experiments were made in Copenhagen three weeks earlier.

[8] M. M. J. Page had already noticed that if a telephone is placed in the circuit of the primary helix of an induction coil, while the secondary helix of this instrument is placed in the circuit of one of M. Lippmann’s capillary electrometers, a movement of the mercurial column of the electrometer takes place at each word, and this movement is effected towards the capillary end of the tube, in whatever direction the current is sent by the telephone. This is because the mercury always tends to move more rapidly at its capillary end than at the other extremity.

[9] Mr. Edison, in a letter written November 25, 1877, writes that he has made two telephones which act with copper diaphragms, based on Arago’s effects of magnetism by rotation. He ascertained that a copper diaphragm might replace the iron plate, if its thickness did not exceed 1/32 of an inch. The effect produced is slight when the copper diaphragm is placed between two corresponding instruments; but when the sender only is furnished with the copper diaphragm, and the receiver is arranged as usual, communication becomes easy.

Mr. Preece repeated these experiments, but he only obtained very slight and indistinct effects: he consequently believes that they are of no practical use, although very interesting in theory.

[10] Mr. Bell had previously made a like experiment, which suggested to him that molecular vibrations had as much to do with the action of the telephone as mechanical vibrations.

[11] M. Bosscha, who has published in the _Archives néerlandaises_ an interesting paper on the intensity of electric currents in the telephone, says that the minimum intensity of currents necessary to produce a sound in a telephone by the vibration of its diaphragm may be less than 100/1000 of a Daniell element, and the displacement of the centre of the diaphragm would then be invisible. He was unable to measure exactly the range of movements produced in the diaphragm by the influence of the voice, but he believes it to be less than the thousandth part of a millimètre; and from this it follows that, for a sound of 880 vibrations, the intensity of the induced currents developed would be 0·0000792 of the unit of electro-magnetic intensity.