Pleasant Ways in Science

In the preceding essay I have described the wonderful instrument called the telephone, which has recently become as widely known in this country as in America, the country of its first development. I propose now briefly to describe another instrument—the phonograph—which, though not a telegraphic instrument, is related in some degree to the telephone. In passing, I may remark that some, who as telegraphic specialists might be expected to know better, have described the phonograph as a telegraphic invention. A writer in the Telegraphic Journal, for instance, who had mistaken for mine a paper on the phonograph in one of our daily newspapers, denounced me (as the supposed author of that paper) for speaking of the possibility of crystallizing sound by means of this instrument; and then went on to speak of the mistake I (that is, said author) had made in leaving my own proper subject of study to speak of telegraphic instruments and to expatiate on the powers of electricity. In reality the phonograph has no relation to telegraphy whatever, and its powers do not in the slightest degree depend on electricity. If the case had been otherwise, it may be questioned whether the student of astronomy, or of any other department of science, should be considered incompetent of necessity to describe a telegraphic instrument, or to discuss the principles of telegraphic or electrical science. What should unquestionably be left to the specialist, is the description of the practical effect of details of instrumental construction, and the like—for only he who is in the habit of using special instruments or classes of instrument can be expected to be competent adequately to discuss such matters.

Although, however, the phonograph is not an instrument depending, like the telephone, on the action of electricity (in some form or other), yet it is related closely enough to the telephone to make the mistake of the Telegraphic journalist a natural one. At least, the mistake would be natural enough for any one but a telegraphic specialist; the more so that Mr. Edison is a telegraphist, and that he has effected several important and interesting inventions in telegraphic and electrical science. For instance, in the previous article, pp. 270, 271, I had occasion to describe at some length the principles of his “Motograph.” I spoke of it as “another form of telephone, surpassing Gray’s and La Cour’s in some respects as a conveyer of musical tones, but as yet unable to speak like Bell’s ... in telegraphic communication.” I proceeded: “Gray’s telephone is limited to about one octave. Edison’s extends from the deepest bass notes to the highest notes of the human voice, which, when magnets are employed, are almost inaudible; but it has yet to learn to speak.”

The phonograph is an instrument which has learned to speak, though it does not speak at a distance like the telephone or the motograph. Yet there seems no special reason why it should not combine both qualities—the power of repeating messages at considerable intervals of time after they were originally spoken, and the power of transmitting them to great distances.

I have said that the phonograph is an instrument closely related to the telephone. If we consider this feature of the instrument attentively, we shall be led to the clearer recognition of the acoustical principles on which its properties depend, and also of the nature of some of the interesting acoustical problems on which light seems likely to be thrown by means of experiments with this instrument.

In the telephone a stretched membrane, or a diaphragm of very flexible iron, vibrates when words are uttered in its neighbourhood. When a stretched membrane is used, with a small piece of iron at the centre, this small piece of iron, as swayed by the vibrations of the membrane, causes electrical undulations to be induced in the coils round the poles of a magnet placed in front of the membrane. These undulations travel along the wire and pass through the coils of another instrument of similar construction at the other end of the wire, where, accordingly, a stretched membrane vibrates precisely as the first had done. The vibrations of this membrane excite atmospheric vibrations identical in character with those which fell upon the first membrane when the words were uttered in its neighbourhood; and therefore the same words appear to be uttered in the neighbourhood of the second membrane, however far it may be from the transmitting membrane, so only that the electrical undulations are effectually transmitted from the sending to the receiving instrument.

I have here described what happened in the case of that earlier form of the telephone in which a stretched membrane of some such substance as goldbeater’s skin was employed, at the centre of which only was placed a small piece of iron. For in its bearing on the subject of the phonograph, this particular form of telephonic diaphragm is more suggestive than the later form in which very flexible iron was employed. We see that the vibrations of a small piece of iron at the centre of a membrane are competent to reproduce all the peculiarities of the atmospheric waves which fall upon the membrane when words are uttered in its neighbourhood. This must be regarded, I conceive, as a remarkable acoustical discovery. Most students of acoustics would have surmised that to reproduce the motions merely of the central parts of a stretched diaphragm would be altogether insufficient for the reproduction of the complicated series of sound-waves corresponding to the utterance of words. I apprehend that if the problem had originally been suggested simply as an acoustical one, the idea entertained would have been this—that though the motions of a diaphragm receiving vocal sound-waves might be generated artificially in such sort as to produce the same vocal sounds, yet this could only be done by first determining what particular points of the diaphragm were centres of motion, so to speak, and then adopting some mechanical arrangements for giving to small portions of the membrane at these points the necessary oscillating motions. It would not, I think, have been supposed that motions communicated to the centre of the diaphragm would suffice to make the whole diaphragm vibrate properly in all its different parts.

Let us briefly consider what was before known about the vibrations of plates, discs, and diaphragms, when particular tones were sounded in their neighbourhood; and also what was known respecting the requirements for vocal sounds and speech as distinguished from simple tones. I need hardly say that I propose only to consider these points in a general, not in a special, manner.

We must first carefully draw a distinction between the vibrations of a plate or disc which is itself the source of sound, and those vibrations which are excited in a plate or disc by sound-waves otherwise originated. If a disc or plate of given size be set in vibration by a blow or other impulse it will give forth a special sound, according to the place where it is struck, or it will give forth combinations of the several tones which it is capable of emitting. On the other hand, experiment shows that a diaphragm like that used in the telephone—not only the electric telephone, but such common telephones as have been sold of late in large quantities in toy shops, etc.—will respond to any sounds which are properly directed towards it, not merely reproducing sounds of different tones, but all the peculiarities which characterize vocal sounds. In the former case, the size of a disc and the conditions under which it is struck determine the nature of its vibrations, and the air responds to the vibrations thus excited; in the latter, the air is set moving in vibrations of a special kind by the sounds or words uttered, and the disc or diaphragm responds to these vibrations. Nevertheless, though it is important that this distinction be recognized, we can still learn, from the behaviour of discs and plates set in vibration by a blow or other impulse, the laws according to which the actual motions of the various parts of a vibrating disc or plate take place. We owe to Chladni the invention of a method for rendering visible the nature of such motions.

Certain electrical experiments of Lichtenberg suggested to Chladni the idea of scattering fine sand over the plate or disc whose motions he wished to examine. If a horizontal plate covered with fine sand is set in vibration, those parts which move upwards and downwards scatter the sand from their neighbourhood, while on those points which undergo no change of position the sand will remain. Such points are called nodes; and rows of such points are called nodal lines, which may be either straight or curved, according to circumstances.

If a square plate of glass is held by a suitable clamp at its centre, and the middle point of a side is touched while a bow is drawn across the edge near a corner, the sand is seen to gather in the form of a cross dividing the square into four equal squares—like a cross of St George. If the finger touches a corner, and the bow is drawn across the middle of a side, the sand forms a cross dividing the square along its diagonals—like a cross of St Andrew. Touching two points equidistant from two corners, and drawing the bow along the middle of the opposite edge, we get the diagonal cross and also certain curved lines of sand systematically placed in each of the four quarters into which the diagonals divide the square. We also have, in this case, a far shriller note from the vibrating plate. And so, by various changes in the position of the points clamped by the finger and of the part of the edge along which the bow is drawn, we can obtain innumerable varieties of nodal lines and curves along which the sand gathers upon the surface of the vibrating plate.

When we take a circular plate of glass, clamped at the middle, and touching one part of its edge with the finger, draw the bow across a point of the edge half a quadrant from the finger, we see the sand arrange itself along two diameters intersecting at right angles. If the bow is drawn at a point one-third a quadrant from the finger-clamped point, we get a six-pointed star. If the bow is drawn at a point a fourth of a quadrant from the finger-clamped point, we get an eight-pointed star. And so we can get the sand to arrange itself into a star of any even number of points; that is, we can get a star of four, six, eight, ten, twelve, etc., points, but not of three, five, seven, etc.

In these cases the centre of the plate or disc has been fixed. If, instead, the plate or disc be fixed by a clip at the edge, or clamped elsewhere than at the centre, we find the sand arranging itself into other forms, in which the centre may or may not appear; that is, the centre may or may not be nodal, according to circumstances.

A curious effect is produced if very fine powder be strewn along with the sand over the plate. For it is found that the dust gathers, not where the nodes or places of no vibration lie, but where the motion is greatest. Faraday assigns as the cause of this peculiarity the circumstance that “the light powder is entangled by the little whirlwinds of air produced by the vibrations of the plate; it cannot escape from the little cyclones, though the heavier sand particles are readily driven through them; when, therefore, the motion ceases, the light powder settles down in heaps at the places where the vibration was a maximum.” In proof of this theory we have the fact that “in vacuo no such effect is produced; all powders light and heavy move to the nodal lines.” (Tyndall on “Sound.”)

Now if we consider the meaning of such results as these, we shall begin to recognize the perplexing but also instructive character of the evidence derived from the telephone, and applied to the construction of the phonograph. It appears that when a disc is vibrating under such special conditions as to give forth a particular series of tones (the so-called fundamental tone of the disc and other tones combined with it which belong to its series of overtones), the various parts of the disc are vibrating to and fro in a direction square to the face of the disc, except certain points at which there is no vibration, these points together forming curves of special forms along the substance of the disc.

When, on the other hand, tones of various kinds are sounded in the neighbourhood of a disc or of a stretched circular membrane, we may assume that the different parts of the disc are set in vibration after a manner at least equally complicated. If the tones belong to the series which could be emitted by the diaphragm when struck, we can understand that the vibrations of the diaphragm would resemble those which would result from a blow struck under special conditions. When other tones are sounded, it may be assumed that the sound-waves which reach the diaphragm cause it to vibrate as though not the circumference (only) but a circle in the substance of the diaphragm—concentric, of course, with the circumference, and corresponding in dimensions with the tone of the sounds—were fixed. If a drum of given size is struck, we hear a note of particular tone. If we heard, as the result of a blow on the same drum, a much higher tone, we should know that in some way or other the effective dimensions of the drum-skin had been reduced—as for instance, by a ring firmly pressed against the inside of the skin. So when a diaphragm is responding to tones other than those corresponding to its size, tension, etc., we infer that the sound-waves reaching it cause it to behave, so far as its effective vibrating portion is concerned, as though its conformation had altered. When several tones are responded to by such a diaphragm, we may infer that the vibrations of the diaphragm are remarkably complicated.

Now the varieties of vibratory motion to which the diaphragm of the telephone has been made to respond have been multitudinous. Not only have all orders of sound singly and together been responded to, but vocal sounds which in many respects differ widely from ordinary tones are repeated, and the peculiarities of intonation which distinguish one voice from another have been faithfully reproduced.

Let us consider in what respects vocal sounds, and especially the sounds employed in speech, differ from mere combinations of ordinary tones.

It has been said, and with some justice, that the organ of voice is of the nature of a reed instrument. A reed instrument, as most persons know, is one in which musical sounds are produced by the action of a vibrating reed in breaking up a current of air into a series of short puffs. The harmonium, accordion, concertina, etc., are reed instruments, the reed for each note being a fine strip of metal vibrating in a slit. The vocal organ of man is at the top of the windpipe, along which a continuous current of air can be forced by the lungs. Certain elastic bands are attached to the head of the windpipe, almost closing the aperture. These vocal chords are thrown into vibration by the current of air from the lungs; and as the rate of their vibration is made to vary by varying their tension, the sound changes in tone. So far, we have what corresponds to a reed instrument admitting of being altered in pitch so as to emit different notes. The mouth, however, affects the character of the sound uttered from the throat. The character of a tone emitted by the throat cannot be altered by any change in the configuration of the mouth; so that if a single tone were in reality produced by the vocal chords, the resonance of the mouth would only strengthen that tone more or less according to the figure given to the cavity of the mouth at the will of the singer or speaker. But in reality, besides the fundamental tone uttered by the vocal chords, a series of overtones are produced. Overtones are tones corresponding to vibration at twice, three times, four times, etc., the rate of the vibration producing the fundamental tone. Now the cavity of the mouth can be so modified in shape as to strengthen either the fundamental tone or any one of these overtones. And according as special tones are strengthened in this way various vocal sounds are produced, without changing the pitch or intensity of the sound actually uttered. Calling the fundamental tone the first tone, the overtones just mentioned the second, third, fourth, etc., tones respectively (after Tyndall), we find that the following relations exist between the combinations of these tones and the various vowel sounds:—

If the lips are pushed forward so as to make the cavity of the mouth deep and the orifice of the mouth small, we get the deepest resonance of which the mouth is capable, the fundamental tone is reinforced, while the higher tones are as far as possible thrown into the shade. The resulting vowel sound is that of deep U (“oo” in “hoop”).

If the mouth is so far opened that the fundamental tone is accompanied by a strong second tone (the next higher octave to the fundamental tone), we get the vowel sound O (as in “hole”). The third and fourth tones feebly accompanying the first and second make the sound more perfect, but are not necessary.

If the orifice of the mouth is so widened, and the volume of the cavity so reduced, that the fundamental tone is lost, the second somewhat weakened, and the third given as the chief tone, with very weak fourth and fifth tones, we have the vowel sound A.

To produce the vowel sound E, the resonant cavity of the mouth must be considerably reduced. The fourth tone is the characteristic of this vowel. Yet the second tone also must be given with moderate strength. The first and third tones must be weak, and the fifth tone should be added with moderate strength.

To produce the vowel sound A, as in “far,” the higher overtones are chiefly used, the second is wanting altogether, the third feeble, the higher tones—especially the fifth and seventh—strong.

The vowel sound I, as in “fine,” it should be added, is not a simple sound, but diphthongal. The two sounds whose succession gives the sound we represent (erroneously) by a single letter I (long), are not very different from “a” as in “far,” and “ee” (or “i” as in “ravine”); they, lie, however, in reality, respectively between “a” in “far” and “fat,” and “i” in “ravine” and “pin.” Thus the tones and overtones necessary for sounding “I” long, do not require a separate description, any more than those necessary for sounding other diphthongs, as “oi,” “oe,” and so forth.

We see, then, that the sound-waves necessary to reproduce accurately the various vowel sounds, are more complicated than those which would correspond to the fundamental tones simply in which any sound may be uttered. There must not only be in each case certain overtones, but each overtone must be sounded with its due degree of strength.

But this is not all, even as regards the vowel sounds, the most readily reproducible peculiarities of ordinary speech. Spoken sounds differ from musical sounds properly so called, in varying in pitch throughout their continuance. So far as tone is concerned, apart from vowel quality, the speech note may be imitated by sliding a finger up the finger-board of a violin while the bow is being drawn. A familiar illustration of the varying pitch of a speech note is found in the utterance of Hamlet’s question, “Pale, or red?” with intense anxiety of inquiry, if one may so speak. “The speech note on the word ‘pale’ will consist of an upward movement of the voice, while that on ‘red’ will be a downward movement, and in both words the voice will traverse an interval of pitch so wide as to be conspicuous to ordinary ears; while the cultivated perception of the musician will detect the voice moving through a less interval of pitch while he is uttering the word ‘or’ of the same sentence. And he who can record in musical notation the sounds which he hears, will perceive the musical interval traversed in these vocal movements, and the place also of these speech notes on the musical staff.” Variations of this kind, only not so great in amount, occur in ordinary speech; and no telephonic or phonographic instrument could be regarded as perfect, or even satisfactory, which did not reproduce them.

But the vowel sounds are, after all, combinations and modifications of musical tones. It is otherwise with consonantal sounds, which, in reality, result from various ways in which vowel sounds are commenced, interrupted (wholly or partially), and resumed. In one respect this statement requires, perhaps, some modification—a point which has not been much noticed by writers on vocal sounds. In the case of liquids, vowel sounds are not partially interrupted only, as is commonly stated. They cease entirely as vowel sounds, though the utterance of a vocal sound is continued when a liquid consonant is uttered. Let the reader utter any word in which a liquid occurs, and he will find that while the liquid itself is sounded the vowel sounds preceding or following the liquid cease entirely. Repeating slowly, for example, the word “remain,” dwelling on all the liquids, we find that while the “r” is being sounded the “ē” sound cannot be given, and this sound ceases so soon as the “m” is sounded; similarly the long “a” sound can only be uttered when the “m” sound ceases, and cannot be carried on into the sound of the final liquid “n.” The liquids are, in fact, improperly called semi-vowels, since no vowel sound can accompany their utterance. The tone, however, with which they are sounded can be modified during their utterance. In sounding labials the emission of air is not stopped completely at any moment. The same is true of the sibilants s, z, sh, zh, and of the consonants g, j, f, v, th (hard and soft). These are called, on this account, continuous consonants. The only consonants in pronouncing which the emission of air is for a moment entirely stopped, are the true mutes, sometimes called the six explosive consonants, b, p, t, d, k, and g.

To reproduce artificially sounds resembling those of the consonants in speech, we must for a moment interrupt, wholly for explosive and partially for continuous consonant sounds, the passage of air through a reed pipe. Tyndall thus describes an experiment of this kind in which an imperfect imitation of the sound of the letter “m” was obtained—an imitation only requiring, to render it perfect, as I have myself experimentally verified, attention to the consideration respecting liquids pointed out in the preceding paragraph. “Here,” says Tyndall, describing the experiment as conducted during a lecture, “is a free reed fixed in a frame, but without any pipe associated with it, mounted on the acoustic bellows. When air is urged through the orifice, it speaks in this forcible manner. I now fix upon the frame of the reed a pyramidal pipe; you notice a change in the clang, and, by pushing my flat hand over the open end of the pipe, the similarity between the sounds produced and those of the human voice is unmistakable. Holding the palm of my hand over the end of the pipe, so as to close it altogether, and then raising my hand twice in quick succession, the word ‘mamma’ is heard as plainly as if it were uttered by an infant. For this pyramidal tube I now substitute a shorter one, and with it make the same experiment. The ‘mamma’ now heard is exactly such as would be uttered by a child with a stopped nose. Thus, by associating with a vibrating reed a suitable pipe, we can impart to the sound of the reed the qualities of the human voice.” The “m” obtained in these experiments was, however, imperfect. To produce an “m” sound such as an adult would utter without a “stopped nose,” all that is necessary is to make a small opening (experiment readily determines the proper size and position) in the side of the pyramidal pipe, so that, as in the natural utterance of this liquid, the emission of air is not altogether interrupted.

I witnessed in 1874 some curious illustrations of the artificial production of vocal sounds, at the Stevens Institute, Hoboken, N.J., where the ingenious Professor Mayer (who will have, I trust, a good deal to say about the scientific significance of telephonic and phonographic experiments before long) has acoustic apparatus, including several talking-pipes. By suitably moving his hand on the top of some of these pipes, he could make them speak certain words with tolerable distinctness, and even utter short sentences. I remember the performance closed with the remarkably distinct utterance, by one profane pipe, of the words euphemistically rendered by Mark Twain (in his story of the Seven Sleepers, I think), “Go thou to Hades!”

Now, the speaking diaphragm in the telephone, as in the phonograph, presently to be described, must reproduce not only all the varieties of sound-wave corresponding to vowel sounds, with their intermixtures of the fundamental tone and its overtones and their inflexions or sliding changes of pitch, but also all the effects produced on the receiving diaphragm by those interruptions, complete or partial, of aerial emission which correspond to the pronunciation of the various consonant sounds. It might certainly have seemed hopeless, from all that had been before known or surmised respecting the effects of aerial vibrations on flexible diaphragms, to attempt to make a diaphragm speak artificially—in other words, to make the movements of all parts of it correspond with those of a diaphragm set in vibration by spoken words—by movements affecting only its central part. It is in the recognition of the possibility of this, or rather in the discovery of the fact that the movements of a minute portion of the middle of a diaphragm regulate the vibratory and other movements of the entire diaphragm, that the great scientific interest of Professor Graham Bell’s researches appears to me to reside.

It may be well, in illustration of the difficulties with which formerly the subject appeared to be surrounded, to describe the results of experiments which preceded, though they can scarcely be said to have led up to, the invention of artificial ways of reproducing speech. I do not now refer to experiments like those of Kratzenstein of St. Petersburg, and Von Kempelen of Vienna, in 1779, and the more successful experiments by Willis in later years, but to attempts which have been made to obtain material records of the aerial motions accompanying the utterance of spoken words. The most successful of these attempts was that made by Mr. W. H. Barlow. His purpose was “to construct an instrument which should record the pneumatic actions” accompanying the utterance of articulated sounds “by diagrams, in a manner analogous to that in which the indicator-diagram of a steam-engine records the action of the engine.” He perceived that the actual aerial pressures involved being very small and very variable, and the succession of impulses and changes of pressure being very rapid, it was necessary that the moving parts should be very light, and that the movement and marking should be accomplished with as little friction as possible. The instrument he constructed consisted of a small speaking-trumpet about four inches long, having an ordinary mouthpiece connected to a tube half an inch in diameter, the thin end of which widened out so as to form an aperture of 2¼ inches diameter. This aperture was covered with a membrane of goldbeater’s skin, or thin gutta-percha. A spring carrying a marker was made to press against the membrane with a slight initial pressure, to prevent as far as possible the effects of jarring and consequent vibratory action. A light arm of aluminium was connected with the spring, and held the marker; and a continuous strip of paper was made to pass under the marker in the manner employed in telegraphy. The marker consisted of a small, fine sable brush, placed in a light tube of glass one-tenth of an inch in diameter, the tube being rounded at the lower end, and pierced with a hole about one-twentieth of an inch in diameter. Through this hole the tip of the brush projected, and was fed by colour put into the glass tube by which it was held. It should be added that, to provide for the escape of air passing through the speaking-trumpet, a small opening was made in the side, so that the pressure exerted upon the membrane was that due to the excess of air forced into the trumpet over that expelled through the orifice. The strength of the spring which carried the marker was so adjusted to the size of the orifice that, while the lightest pressures arising under articulation could be recorded, the greatest pressures should not produce a movement exceeding the width of the paper.

“It will be seen,” says Mr. Barlow, “that in this construction of the instrument the sudden application of pressure is as suddenly recorded, subject only to the modifications occasioned by the inertia, momentum, and friction of the parts moved. But the record of the sudden cessation of pressure is further affected by the time required to discharge the air through the escape-orifice. Inasmuch, however, as these several effects are similar under similar circumstances, the same diagram should always be obtained from the same pneumatic action when the instrument is in proper adjustment; and this result is fairly borne out by the experiments.”

The defect of the instrument consisted in the fact that it recorded changes of pressure only; and in point of fact it seems to result, from the experiments made with it, that it could only indicate the order in which explosive, continuant, and liquid consonants succeeded each other in spoken words, the vowels being all expressed in the same way, and only one letter—the rough R, or R with a burr—being always unmistakably indicated. The explosives were represented by a sudden sharp rise and fall in the recorded curve; the height of the rise depending on the strength with which the explosive is uttered, not on the nature of the consonant itself. Thus the word “tick” is represented by a higher elevation for the “t” than for the “k,” but the word “kite” by a higher elevation for the “k” than for the “t.” It is noteworthy that there is always a second smaller rise and fall after the first chief one, in the case of each of the explosives. This shows that the membrane, having first been forcibly distended by the small aerial explosion accompanying the utterance of such a consonant, sways back beyond the position where the pressure and the elasticity of the membrane would (for the moment) exactly balance, and then oscillates back again over that position before returning to its undistended condition. Sometimes a third small elevation can be recognized, and when an explosive is followed by a rolling “r” several small elevations are seen. The continuous consonants produce elevations less steep and less high; aspirates and sibilants give rounded hills. But the results vary greatly according to the position of a consonant; and, so far as I can make out from a careful study of the very interesting diagrams accompanying Mr. Barlow’s paper, it would be quite impossible to define precisely the characteristic records even of each order of consonantal sounds, far less of each separate sound.

We could readily understand that the movement of the central part of the diaphragm in the telephone should give much more characteristic differences for the various sounds than Barlow’s logograph. For if we imagine a small pointer attached to the centre of the face of the receiving diaphragm while words are uttered in its neighbourhood, the end of that pointer would not only move to and fro in a direction square to the face of the diaphragm, as was the case with Barlow’s marker, but it would also sway round its mean position in various small circles or ovals, varying in size, shape, and position, according to the various sounds uttered. We might expect, then, that if in any way a record of the actual motions of the extremity of that small pointer could be obtained, in such sort that its displacement in directions square to the face of the diaphragm, as well as its swayings around its mean position, would be indicated in some pictorial manner, the study of such records would indicate the exact words spoken near the diaphragm, and even, perhaps, the precise tones in which they were uttered. For Barlow’s logograph, dealing with one only of the orders of motion (really triple in character), gives diagrams in which the general character of the sounds uttered is clearly indicated, and the supposed records would show much more.

But although this might, from à priori considerations, have been reasonably looked for, it by no means follows that the actual results of Bell’s telephonic experiments could have been anticipated. That the movement of the central part of the diaphragm should suffice to show that such and such words had been uttered, is one thing; but that these movements should of themselves suffice, if artificially reproduced, to cause the diaphragm to reproduce these words, is another and a very different one. I venture to express my conviction that at the beginning of his researches Professor Bell can have had very little hope that any such result would be obtained, notwithstanding some remarkable experiments respecting the transmission of sound which we can now very clearly perceive to point in that direction.

When, however, he had invented the telephone, this point was in effect demonstrated; for in that instrument, as we have seen, the movements of the minute piece of metal attached (at least in the earlier forms of the instrument) to the centre of the receiving membrane, suffice, when precisely copied by the similar central piece of metal in the transmitting membrane, to cause the words which produced the motions of the receiving or hearing membrane to be uttered (or seem to be uttered) by the transmitting or speaking membrane.

It was reserved, however, for Edison (of New Jersey, U.S.A., Electrical Adviser to the Western Union Telegraph Company) to show how advantage might be taken of this discovery to make a diaphragm speak, not directly through the action of the movements of a diaphragm affected by spoken words or other sounds, and therefore either simultaneously with these or in such quick succession after them as corresponds with the transmission of their effects along some line of electrical or other communication, but by the mechanical reproduction of similar movements at any subsequent time (within certain limits at present, but probably hereafter with practically unlimited extension as to time).

The following is slightly modified from Edison’s own description of the phonograph:—

The instrument is composed of three parts mainly; namely, a receiving, a recording, and a transmitting apparatus. The receiving apparatus consists of a curved tube, one end of which is fitted with a mouthpiece. The other end is about two inches in diameter, and is closed with a disc or diaphragm of exceedingly thin metal, capable of being thrust slightly outwards or vibrated upon gentle pressure being applied to it from within the tube. To the centre of this diaphragm (which is vertical) is fixed a small blunt steel pin, which shares the vibratory motion of the diaphragm. This arrangement is set on a table, and can be adjusted suitably with respect to the second part of the instrument—the recorder. This is a brass cylinder, about four inches in length and four in diameter, cut with a continuous V-groove from one end to the other, so that in effect it represents a large screw. There are forty of these grooves in the entire length of the cylinder. The cylinder turns steadily, when the instrument is in operation, upon a vertical axis, its face being presented to the steel point of the receiving apparatus. The shaft on which it turns is provided with a screw-thread and works in a screwed bearing, so that as the shaft is turned (by a handle) it not only turns the cylinder, but steadily carries it upwards. The rate of this vertical motion is such that the cylinder behaves precisely as if its groove worked in a screw-bearing. Thus, if the pointer be set opposite the middle of the uppermost part of the continuous groove at the beginning of this turning motion, it will traverse the groove continuously to its lowest part, which it will reach after forty turnings of the handle. (More correctly, perhaps, we might say that the groove continuously traverses past the pointer.) Now, suppose that a piece of some such substance as tinfoil is wrapped round the cylinder. Then the pointer, when at rest, just touches the tinfoil. But when the diaphragm is vibrating under the action of aerial waves resulting from various sounds, the pointer vibrates in such a way as to indent the tinfoil—not only to a greater or less depth according to the play of the pointer to and fro in a direction square to the face of the diaphragm, but also over a range all round its mean position, corresponding to the play of the end of the pointer around its mean position. The groove allows the pressure of the pointer against the tinfoil free action. If the cylinder had no groove the dead resistance of the tinfoil, thus backed up by an unyielding surface, would stop the play of the pointer. Under the actual conditions, the tinfoil is only kept taut enough to receive the impressions, while yielding sufficiently to let the play of the pointer continue unrestrained. If now a person speaks into the receiving tube, and the handle of the cylinder be turned, the vibrations of the pointer are impressed upon the portion of the tinfoil lying over the hollow groove, and are retained by it. They will be more or less deeply marked according to the quality of the sounds emitted, and according also, of course, to the strength with which the speaker utters the sounds, and to the nature of the modulations and inflexions of his voice. The result is a message verbally imprinted upon a strip of metal. It differs from the result in the case of Barlow’s logograph, in being virtually a record in three dimensions instead of one only. The varying depth of the impressions corresponds to the varying height of the curve in Barlow’s diagrams; but there the resemblance ceases; for that was the single feature which Barlow’s logographs could present. Edison’s imprinted words show, besides varying depth of impression, a varying range on either side of the mean track of the pointer, and also—though the eye is not able to detect this effect—there is a varying rate of progression according as the end of the pointer has been swayed towards or from the direction in which, owing to the motion of the cylinder, the pointer is virtually travelling.

We may say of the record thus obtained that it is sound presented in a visible form. A journalist who has written on the phonograph has spoken of this record as corresponding to the crystallization of sound. And another who, like the former, has been (erroneously, but that is a detail) identified with myself, has said, in like fanciful vein, that the story of Baron Münchausen hearing words which had been frozen during severe cold melting into speech again, so that all the babble of a past day came floating about his ears, has been realized by Edison’s invention. Although such expressions may not be, and in point of fact are not, strictly scientific, I am not disposed, for my own part, to cavil with them. If they could by any possibility be taken au pied de la lettre (and, by the way, we find quite a new meaning for this expression in the light of what is now known about vowels and consonants), there would be valid objection to their use. But, as no one supposes that Edison’s phonograph really crystallizes words or freezes sounds, it seems hypercritical to denounce such expressions as the critic of the Telegraphic Journal has denounced them.

To return to Edison’s instrument.

Having obtained a material record of sounds, vocal or otherwise, it remains that a contrivance should be adopted for making this record reproduce the sounds by which it was itself formed. This is effected by a third portion of the apparatus, the transmitter. This is a conical drum, or rather a drum shaped like a frustum of a cone, having its larger end open, the smaller—which is about two inches in diameter—being covered with paper stretched tight like the parchment of a drumhead. In front of this diaphragm is a light flat steel spring, held vertically, and ending in a blunt steel point, which projects from it and corresponds precisely with that on the diaphragm of the receiver. The spring is connected with the paper diaphragm by a silken thread, just sufficiently in tension to cause the outer face of the diaphragm to be slightly convex. Having removed the receiving apparatus from the cylinder and set the cylinder back to its original position, the transmitting apparatus is brought up to the cylinder until the steel point just rests, without pressure, in the first indentation made in the tinfoil by the point of the receiver. If now the handle is turned at the same speed as when the message was being recorded, the steel point will follow the line of impression, and will vibrate in periods corresponding to the impressions which were produced by the point of the receiving apparatus. The paper diaphragm being thus set into vibrations of the requisite kind in number, depth, and side-range, there are produced precisely the same sounds that set the diaphragm of the receiver into vibration originally. Thus the words of the speaker are heard issuing from the conical drum in his own voice, tinged with a slightly metallic or mechanical tone. If the cylinder be more slowly turned when transmitting than it had been when receiving the message, the voice assumes a base tone; if more quickly, the message is given with a more treble voice. “In the present machine,” says the account, “when a long message is to be recorded, so soon as one strip of tinfoil is filled, it is removed and replaced by others, until the communication has been completed. In using the machine for the purpose of correspondence, the metal strips are removed from the cylinder and sent to the person with whom the speaker desires to correspond, who must possess a machine similar to that used by the sender. The person receiving the strips places them in turn on the cylinder of his apparatus, applies the transmitter, and puts the cylinder in motion, when he hears his friend’s voice speaking to him from the indented metal. And he can repeat the contents of the missive as often as he pleases, until he has worn the metal through. The sender can make an infinite number of copies of his communication by taking a plaster-of-Paris cast of the original, and rubbing off impressions from it on a clean sheet of foil.”

I forbear from dwelling further on the interest and value of this noble invention, or of considering some of the developments which it will probably receive before long, for already I have occupied more space than I had intended. I have no doubt that in these days it will bring its inventor less credit, and far less material gain, than would be acquired from the invention of some ingenious contrivance for destroying many lives at a blow, bursting a hole as large as a church door in the bottom of an ironclad, or in some other way helping men to carry out those destructive instincts which they inherit from savage and brutal ancestors. But hereafter, when the representatives of the brutality and savagery of our nature are held in proper disesteem, and those who have added new enjoyments to life are justly valued, a high place in the esteem of men will be accorded to him who has answered one-half of the poet’s aspiration,

Note.—Since the present paper was written, M. Aurel de Ratti has made some experiments which he regards as tending to show that there is no mechanical vibration. Thus, “when the cavities above and below the iron disc of an ordinary telephone are filled with wadding, the instrument will transmit and speak with undiminished clearness. On placing a finger on the iron disc opposite the magnet, the instrument will transmit and speak distinctly, only ceasing to act when sufficient pressure is applied to bring plate and magnet into contact. Connecting the centre of the disc by means of a short thread with an extremely sensitive membrane, no sound is given out by the latter when a message is transmitted. Bringing the iron cores of the double telephone in contact with the disc, and pressing with the fingers against the plate on the other side, a weak current from a Daniell cell produced a distinct click in the plate, and on drawing a wire from the cell over a file which formed part of the circuit, a rattling noise was produced in the instrument.” If these experiments had been made before the phonograph was invented, they would have suggested the impracticability of constructing any instrument which would do what the phonograph actually does, viz., cause sounds to be repeated by exciting a merely mechanical vibration of the central part of a thin metallic disc. But as the phonograph proves that this can actually be done, we must conclude that M. Aurel de Ratti’s experiments will not bear the interpretation he places upon them. They show, nevertheless, that exceedingly minute vibrations of probably a very small portion of the telephonic disc suffice for the distinct transmission of vocal sounds. This might indeed be inferred from the experiments of M. Demozet, of Nantes, who finds that the vibrations of the transmitting telephone are in amplitude little more than 1-2000th those of the receiving telephone.