Part 18

The speaker stands before the mouthpiece E, as before a telephone or an acoustic tube, and speaks in a strong, emphatic voice, with his lips pressed against the walls of the mouthpiece, as we see in fig. 67; at the same moment he turns the handle of the cylinder, which is provided with a heavy fly-wheel in order that the movement may be regular. Influenced by the voice, the plate L L begins to vibrate, and sets the tracing point at work, which presses on the tinfoil at each vibration, and produces a furrow whose depth varies along its course in correspondence with the unequal vibrations of the disk. The cylinder which moves at the same time presents the different parts of the groove of which we have spoken to the tracing point in succession; so that when the spoken sentence comes to an end, the design which has been pricked out, consisting of a succession of reliefs and depressions, represents the registration of the sentence itself. The first part of the operation is therefore accomplished, and by detaching the sheet from the instrument the words may be put away in a portfolio. We have now to see how the instrument is able to reproduce what has been so easily inscribed.

For this purpose it is only necessary to repeat the process, and the identical effect will be reproduced in an inverse sense. The tracing stylus is replaced at the end of the groove it has already traversed, and the cylinder is again set in motion. When the engraved track passes again under the point, it has a tendency to raise it and to impart to it movements which must necessarily be the repetition of those which first produced the tracing. The vibrating plate is obedient to these movements, and begins to vibrate, thus producing the same sounds, and consequently the same words; yet since there is necessarily a loss of power in this double transformation of mechanical effects, the speaking tube C is attached to the mouthpiece E in order to intensify the effects. Under these conditions the words reproduced by the instrument may be heard in all parts of a hall, and it is startling to hear this voice--somewhat shrill, it must be admitted--which seems to utter its sentences from beyond the grave. If this invention had taken place in the middle ages, it would certainly have been applied to ghostly apparitions, and it would have been invaluable to miracle-mongers.

[Illustration: FIG. 68.]

As the height of the notes of the musical scale depends on the number of vibrations effected by a vibrating substance in a given time, speaking will be reproduced in a tone of which the pitch will depend on the velocity of rotation given to the cylinder on which the tinfoil is wound. If the velocity is the same as that which was used in registration, the tone of the words reproduced is the same as that in which they were uttered. If the velocity is greater, the tone is higher; if less, the tone is lower; but the accent of the speaker may always be recognised. Owing to this peculiarity the reproduction of songs is nearly always defective in instruments turned by the hand; they sing out of tune. This is not the case when the instrument is moved by a well-regulated system of clockwork, and in this way a satisfactory reproduction of a duet has been obtained.

The words registered on tinfoil can be often reproduced; but the sounds become fainter and more indistinct at each repetition, since the tracings in relief are gradually effaced. The reproduction on copper is more successful, but if intended to be permanent the sheets must be stereotyped, and in this case the instrument must be differently arranged.

An attempt has been made to obtain speech from the phonograph by taking the words registered inversely to their true direction. In this way the sounds obtained were necessarily quite unlike the words uttered; yet Messrs. Fleeming Jenkin and Ewing have observed that not only are the vowels unchanged by this inverse action, but consonants, syllables, and even whole words may be reproduced with the accent they would have if spoken backwards.

The sounds produced by the phonograph, although fainter than those of the voice which produced the registered tracing, are strong enough to react on the ordinary string telephone, and even on a Bell telephone; and as in this case the sounds do not go beyond the instrument, and can only be heard by the person who is using it, it is easy to ascertain that the sound has not been produced by trickery.

Mr. Edison presented his phonograph to the Académie des Sciences through me, March 11, 1878, and when his agent, M. Puskas, caused the wonderful instrument to speak, a murmur of admiration was heard from all parts of the hall--a murmur succeeded by repeated applause. A letter appeared in the newspapers from one of the persons present, in which he said that ‘the learned Academy, generally so cold, had never before abandoned itself to such enthusiasm. Yet some members of a sceptical turn of mind, instead of examining the physical fact, ascribed it to moral causes, and a report soon ran through the room which seemed to accuse the Academy of having been mystified by a clever ventriloquist. Certainly the spirit of ancient Gaul is still to be found among the French, and even in the Academy. One said that the sounds emitted by the instrument were precisely those of a ventriloquist. Another asked if the movements of M. Puskas’ face and lips as he turned the instrument did not resemble the grimaces of a ventriloquist. A third admitted that the phonograph might emit sounds, but believed that it was much helped by the manipulator. Finally, the Academy requested M. du Moncel to try the experiment, and as he was not accustomed to speak into the instrument, it was unsuccessful, to the great joy of the incredulous. Some members of the Academy, however, desiring to ascertain the real nature of the effects, begged M. Puskas to repeat the experiments before them in the secretary’s office under such conditions as they should lay down. M. Puskas complied with this request, and they were absolutely satisfied with the result. Yet others remained incredulous, and it was necessary that they should make the experiment for themselves before they accepted the fact that speech could be reproduced in so simple a way.’

The anecdote I have just related cannot be interpreted to the discredit of the Académie des Sciences, since it is especially bound to preserve the true principles of science intact, and only to accept startling facts after a careful examination. Owing to this attitude, all which emanates from the Academy can be received with complete confidence; and we cannot approve too highly of reserve which does not give way to the first impulse of enthusiasm and admiration.

The failure of my experiment at the Academy was simply due to the fact that I spoke at too great a distance from the vibrating disk, and that my lips did not touch the sides of the mouthpiece. Some days later, at the request of several of my colleagues, I made repeated trials of the instrument, and I soon succeeded in making it speak as well as the supposed ventriloquist; but I learned at the same time that practice is necessary to ensure success. Some words are reproduced more readily than others; those which include many vowels and many _r_’s come out better than those which abound in consonants, and especially in _s_’s. It is therefore not surprising that, even in the case of an experienced manipulator like Mr. Edison’s agent, some of the sentences uttered by him are more audible than others.

The simultaneous repetition of several sentences in different languages by registering one over the other is one of the most surprising effects of the phonograph. As many as three different sentences have been obtained; but in order to distinguish them through the confused sounds which result from placing one over the other, it is necessary that different persons, giving special attention to a particular sentence, should thus separate them and understand their sense. Vocal airs may, in the same way, be registered over the word tracings, and in this case it is more easy to distinguish them.

There are several models of phonographs. The one represented in fig. 66 has been chiefly used for public experiments, but there is a small model, generally sold to the public, in which the cylinder is much longer, and serves at once for register and fly-wheel. This instrument gives good results, but can only be used for short sentences. In this model, as indeed in the other, the words are more easily registered by fastening a small tube in the form of a prolonged speaking-trumpet to the mouthpiece; the vibrations of the air are thus concentrated on the vibrating disk, and act with greater energy. The tenuity of the vibrating disk adds to the efficiency of the instrument, and the tracing point may be fitted directly to this disk.

[Illustration: FIG. 69.]

I need not describe particularly the phonograph which acts by clockwork. The instrument resembles the one represented fig. 66, except that it is mounted on a rather high table, to give room for the descent of the weight which moves the clockwork; the mechanism is applied directly to the axis of the cylinder, supplying the place of the winch, and is regulated by a small fly-wheel. The wheel used in an English system has been adopted, but we prefer that of M. Villarceau, which has small wings.

Since it is always difficult to fit the tinfoil to the cylinder, Mr. Edison has tried, with good success, to obtain the tracing on a plane surface of tinfoil, by means of the arrangement represented fig. 69. In this new model, the plate on which the tin or copper sheet is to be applied has a spiral grooving, of which one end corresponds to the centre of the plate, and the other to its outer edges. The plate is set in motion by a powerful system of clockwork, of which the velocity is regulated with reference to the length of the turns of the spiral. The vibrating disk is arranged as in the former instrument, and is placed above this plate; the tracing point may, by means of a movement of progression imparted to the system, follow the spiral groove from the centre of the plate to its circumference.

It must not be supposed that all the tinfoil used for phonographic registration is equally good. The foil must be of a definite thickness, and combined with a definite amount of lead. That which is used for wrapping chocolate, and indeed all foil of French manufacture, is too thin and too exclusively made of tin to produce good results, and M. Puskas was obliged to import some from America to continue his experiments. The relative proportion of lead and tin has not yet been defined, and the selection of foil has been made empirically; but as the use of the phonograph becomes more general, this proportion must be ascertained, and it may easily be done by analysing the composition of the foil which gives the best results.

[Illustration: FIG. 70.]

The arrangement of the tracing point is also of much importance for the successful action of the phonograph. It must be very slender and very short (not exceeding a millimètre in length), so as to register distinctly the smallest vibrations of the vibrating disk without deviating from the normal direction of the cylinder, which might be the case, if it were long, on account of the unequal friction exerted on the tinfoil. It must also be made of a metal which has no tendency to tear the metallic sheet. Iron appears to combine most of the conditions demanded.

The phonograph is still in its infancy, and it is probable that it may soon be enabled to register speech without the necessity of speaking into a mouthpiece. According to the newspapers, Mr. Edison has already discovered a way of collecting, without the aid of an acoustic tube, the sounds uttered at a distance of three or four feet from the instrument, and of printing them on a metallic sheet. From this there is only a step to the power of inscribing a speech uttered in a large hall at any distance from the phonograph; and if this step is taken, phonography may be substituted with advantage for shorthand. We add in a note the instructions given by M. Roosevelt to the purchasers of phonographs, so as to enable them to work the instrument.[20]

_Considerations on the theory._--Although the explanation we have given will make the effects of the phonograph intelligible, it leads to a curious question which has greatly interested physicists--namely, how it is that the tracing made on so yielding a surface as tin can, when retraced by the stylus, of which the rigidity is relatively great, produce a vibratory movement without being completely destroyed. To this we reply that the retracing is effected with such extreme rapidity that the effects of active force which are developed only manifest themselves locally, and that under these conditions the mechanical effects exerted are as energetic in soft as in hard substances. The curious experiment, related in so many books on physics, must be remembered, of a plank pierced when a candle serves as the projectile of a gun. The various accidents caused by the discharge of paper waddings must also be remembered. Under such conditions the motion imparted to the molecules which receive the shock has not time to be transmitted to the whole mass of the substance to which they belong, and these molecules are compelled to separate from it, or at any rate to produce, when the substance is capable of vibration, a centre of vibration which diffuses waves throughout its surface, and produces sounds.

Several scientific men, among others Messrs. Preece and Mayer, have carefully studied the form of the tracing left by the voice on the tinfoil of the phonograph, and they observe that it greatly resembles the outline of the singing flames so well shown by Herr Koenig’s instruments. Mr. Mayer wrote on this subject in the ‘Popular Science Monthly Review’ of April 1878.

He said that he had been successful in reproducing a splendid tracing on smoked glass, which gave in profile the outline of the vibrations of sound registered on the tinfoil with their varying curves. For this purpose he fastened to the spring support of the tracing point of the phonograph a slender rod, terminating in a point, which pressed obliquely against the plate of smoked glass, and, since the latter was in a vertical position, a movement imparted to the rod enabled it to produce a sinusoidal tracing. By this arrangement, when the phonograph was at work, two systems of tracings were produced at the same moment, of which one was the profile of the other.

Mr. Mayer had not, at the time he wrote, been long enough in possession of the instrument to make many experiments with it, but from a study of some of its curves it appeared to him that the registered outlines bore a strong resemblance to those of Koenig’s singing flames.

[Illustration: FIG. 71.]

Fig. 71 represents the tracing which corresponds to the letter _a_ when pronounced as in _bat_, in the three systems of registration. That corresponding to line A is an enlarged reproduction of the tracing left on the tinfoil; that corresponding to line B represents its profile on the sheet of smoked glass. Finally, line C shows the outline of Koenig’s singing flames, when the same sound is produced quite close to the membrane of the register. It must be quite close, since the form of the tracing produced by a pointer attached to a vibrating membrane, when influenced by composite sounds, depends on the distance intervening between the membrane and the source of sound, and an infinite variety in the form of the tracing may be obtained by modifying the distance. In fact, when this distance is increased, the waves of sound which result from composite sounds react on the membrane at different moments of their emission. For example, if the composite sound is formed of six harmonics, the displacement of the source of vibration from the first harmonic by ¼ the length of a wave will respectively remove the second, third, fourth, fifth, and sixth harmonics ½, ¾, 1, 1¼, 1½ the length of a wave, and consequently the outline resulting from the combination of waves will no longer be the same as it was before the displacement of the source of sound, although the perception of the sounds remains the same in both cases. This principle is clearly demonstrated by Koenig’s instrument, by lengthening and shortening an extensible tube, inserted between the resonator and the vibrating membrane, which is placed close to the flame; and this explains the disagreement of physicists as to the composition of vocal sounds which they have analysed by means of the singing flames.

Mr. Mayer adds that these facts further show that we cannot hope to read the impressions and tracings of the phonograph, which not only vary with the nature of the voice, but also with the different moments at which the harmonics of the voice are emitted, and with the relative differences in the intensities of these harmonics.

Notwithstanding this assertion, we reproduce (fig. 72) an extremely curious tracing sent to us by Mr. Blake, which represents the vibrations produced by the words ‘Brown, University: how do you do?’ They were photographed by means of an index fastened to a vibrating disk on which a ray of light was thrown. The word ‘how’ is particularly remarkable for the combined forms of the inflections of the vibrations.

Recent experiments seem to show that the more the vibrating membrane of the phonograph resembles the human ear in its construction, the better it repeats and registers the sound vibrations: it should be stretched, as far as possible, in the same way as the tympanum is stretched by the hammer of the ear, and moreover it should have the same form, since the vibrations of air are in this case much more effective.

[Illustration: FIG. 72.]

Mr. Edison considers that the size of the opening of the mouthpiece has considerable influence on the distinct articulation of speech. When the sounds are pronounced before the whole surface of the diaphragm, some hissing sounds are lost. They are, on the contrary, intensified when these sounds reach the diaphragm through a narrow orifice with sharp rims. If the opening is toothed on its flattened rims, the hissing consonants are delivered more clearly. Speech is reproduced more perfectly when the mouthpiece has a covering of some thickness, so arranged as to deaden the sounds arising from the friction of the tracing point on the tin.

Mr. Hardy has rendered the registration of phonographic tracings more easy by adding a small ebonite tube, resembling the mouthpiece of a wind instrument, to the mouthpiece of the phonograph.

USES OF THE PHONOGRAPH AND ITS FUTURE.

Mr. Edison has lately published in the ‘North American Review’ of May-June 1878 an article on the future of the phonograph, in which he himself discusses the different applications which may be made of this instrument. Without sharing all his anticipations, which appear to us to be very premature, we think that some extracts from his paper may be interesting.

‘In order to furnish a basis on which the reader may take his stand ... a few categorical questions and answers are given upon the essential features of the principle involved.

‘1. Is a vibrating plate or disk capable of receiving a complex motion which shall correctly represent the peculiar property of each and all the multifarious vocal and other sound waves?

‘The telephone answers affirmatively.

‘2. Can such complex movement be transmitted from such plate by means of a single embossing point attached thereto, to effect a record upon a plastic material, by indentation, with such fidelity as to give to such indentations the same varied and complex form? And if so, will this embossing point, upon being passed over the record thus made, follow it with such fidelity as to transmit to the disk the same variety of movement, and thus effect a restoration or reproduction of the vocal or other sound waves, without loss of any property essential to producing on the ear the same sensation as if coming direct from the original source?

‘The answer to this may be summed up in a statement of the fact that ... the writer has at various times during the past weeks reproduced these waves with such degree of accuracy in each and every detail as to enable his assistants to read, without the loss of a word, one or more columns of a newspaper article unfamiliar to them, and which were spoken into the apparatus when they were not present. The only perceptible loss was found to be in the quality of the utterance, a non-essential in the practical application of the instrument. Indeed, the articulation of some individuals has been perceptibly improved by passage through the phonograph, the original utterance being mutilated by some imperfection of lip and mouth formation, and these mutilations corrected or eliminated by the mechanism of the phonograph.[21]

‘3. Can a record be removed from the apparatus on which it was made, and replaced upon a second without mutilation or loss of effective power to vibrate the second plate?

‘This is a mere mechanical detail, presenting no greater obstacle than having proper regard for the perfect interchangeableness of the various working parts of the apparatus--not so nice a problem as the manufacture of the American watch.

‘4. What as to the facility of placing and removing the second sheet, and as to its transportation by mail?

‘But ten or fifteen seconds suffice for such placing or removing. A special envelope will probably be required, the weight and form of which, however, will but slightly increase the cost of postage.

‘5. What as to durability?

‘Repeated experiments have proved that the indentations possess wonderful enduring power, even when the reproduction has been effected by the comparatively rigid plate used for their production. It is proposed, however, to use a more flexible plate for reproducing, which, with a perfectly smooth stone point--diamond or sapphire--will render the record capable of from fifty to one hundred repetitions, enough for all practical purposes.

‘6. What as to duplication of a record and its permanence?

‘Many experiments have been made, with more or less success, in the effort to obtain electrotypes of a record, and the writer is informed that it has very recently been successfully accomplished. He can certainly see no great practical obstacle in the way. This, of course, permits of an indefinite multiplication of a record, and its preservation for all time.

‘7. What is the requisite force of wave impinging upon the diaphragm, and the proximity of the mouth to the diaphragm, to effect a record?

‘These depend in great measure upon the volume of sound desired in the reproduction. If the reproduction is to be made audible to an assembly, considerable force is requisite in the original utterance; if for the individual ear, only the ordinary conversational tone (even a whisper has been reproduced). In both cases the original utterances are delivered directly in the mouthpiece of the instrument. An audible reproduction may, however, be had by speaking at the instrument from a distance of from two to three feet in loud tone. The application of a flaring tube or funnel to collect the sound waves, and the construction of an especially delicate diaphragm and embossing point, &c., are the simple means which suggest themselves to effect this....