Heroes of the Telegraph Part 11

Although Edison was the master spirit of the band, it must not be forgotten that his a.s.sistants were sometimes co-inventors with himself.

No doubt he often supplied the germinal ideas, while his a.s.sistants only carried them out. But occasionally the suggestion was nothing more than this: 'I want something that will do so-and-so. I believe it will be a good thing, and can be done.' The a.s.sistant was on his mettle, and either failed or triumphed. The results of the experiments and researches were all chronicled in a book, for the new facts, if not then required, might become serviceable at a future time. If a rare material was wanted, it was procured at any cost.

With such facilities, an invention is rapidly matured. Sometimes the idea was conceived in the morning, and a working model was constructed by the evening. One day, we are told, a discovery was made at 4 P.M., and Edison telegraphed it to his patent agent, who immediately drew up the specification, and at nine o'clock next morning cabled it to London.

Before the inventor was out of bed, he received an intimation that his patent had been already deposited in the British Patent Office. Of course, the difference of time was in his favour.

When Edison arrived at the laboratory in the morning, he read his letters, and then overlooked his employees, witnessing their results and offering his suggestions; but it often happened that he became totally engrossed with one experiment or invention. His work was frequently interrupted by curious visitors, who wished to see the laboratory and the man. Although he had chosen that out-of-the-way place to avoid disturbance, they were never denied: and he often took a pleasure in showing his models, or explaining the work on which he was engaged.

There was no affectation of mystery, no attempt at keeping his experiments a secret. Even the laboratory notes were open to inspection.

Menlo Park became a kind of Mecca to the scientific pilgrim; the newspapers and magazines despatched reporters to the scene; excursion parties came by rail, and country farmers in their buggies; till at last an enterprising Yankee even opened a refreshment room.

The first of Edison's greater inventions in Menlo Park was the 'loud-speaking telephone.' Professor Graham Bell had introduced his magneto-electric telephone, but its effect was feeble. It is, we believe, a maxim in biology that a similarity between the extremities of a creature is an infallible sign of its inferiority, and that in proportion as it rises in the scale of being, its head is found to differ from its tail. Now, in the Bell apparatus, the transmitter and the receiver were alike, and hence Clerk Maxwell hinted that it would never be good for much until they became differentiated from each other.

Consciously or unconsciously Edison accomplished the feat. With the hardihood of genius, he attempted to devise a telephone which would speak out loud enough to be heard in any corner of a large hall.

In the telephone of Bell, the voice of the speaker is the motive power which generates the current in the line. The vibrations of the sound may be said to transform themselves into electrical undulations. Hence the current is very weak, and the reproduction of the voice is relatively faint. Edison adopted the principle of making the vibrations of the voice control the intensity of a current which was independently supplied to the line by a voltaic battery. The plan of Bell, in short, may be compared to a man who employs his strength to pump a quant.i.ty of water into a pipe, and that of Edison to one who uses his to open a sluice, through which a stream of water flows from a capacious dam into the pipe. Edison was acquainted with two experimental facts on which to base the invention.

In 1873, or thereabout, he claimed to have observed, while constructing rheostats, or electrical resistances for making an artificial telegraph line, that powdered plumbago and carbon has the property of varying in its resistance to the pa.s.sage of the current when under pressure. The variation seemed in a manner proportional to the pressure. As a matter of fact, powdered carbon and plumbago had been used in making small adjustable rheostats by M. Clerac, in France, and probably also in Germany, as early as 1865 or 1866. Clerac's device consisted of a small wooden tube containing the material, and fitted with contacts for the current, which appear to have adjusted the pressure. Moreover, the Count Du Moncel, as far back as 1856, had clearly discovered that when powdered carbon was subjected to pressure, its electrical resistance altered, and had made a number of experiments on the phenomenon. Edison may have independently observed the fact, but it is certain he was not the first, and his claim to priority has fallen to the ground.

Still he deserves the full credit of utilising it in ways which were highly ingenious and bold. The 'pressure-relay,' produced in 1877, was the first relay in which the strength of the local current working the local telegraph instrument was caused to vary in proportion to the variation; of the current in the main line. It consisted of an electro-magnet with double poles and an armature which pressed upon a disc or discs of plumbago, through which the local current Pa.s.sed. The electro-magnet was excited by the main line current and the armature attracted to its poles at every signal, thus pressing on the plumbago, and by reducing its resistance varying the current in the local circuit.

According as the main line current was strong or weak, the pressure on the plumbago was more or less, and the current in the local circuit strong or weak. Hence the signals of the local receiver were in accordance with the currents in the main line.

Edison found that the same property might be applied to regulate the strength of a current in conformity with the vibrations of the voice, and after a great number of experiments produced his 'carbon transmitter.' Plumbago in powder, in sticks, or rubbed on fibres and sheets of silk, were tried as the sensitive material, but finally abandoned in favour of a small cake or wafer of compressed lamp-black, obtained from the smoke of burning oil, such as benzolene or rigolene.

This was the celebrated 'carbon b.u.t.ton,' which on being placed between two platinum discs by way of contact, and traversed by the electric current, was found to vary in resistance under the pressure of the sound waves. The voice was concentrated upon it by means of a mouthpiece and a diaphragm.

The property on which the receiver was based had been observed and applied by him some time before. When a current is pa.s.sed from a metal contact through certain chemical salts, a lubricating effect was noticeable. Thus if a metal stylus were rubbed or drawn over a prepared surface, the point of the stylus was found to slip or 'skid' every time a current pa.s.sed between them, as though it had been oiled. If your pen were the stylus, and the paper on which you write the surface, each wave of electricity pa.s.sing from the nib to the paper would make the pen start, and jerk your fingers with it. He applied the property to the recording of telegraph signals without the help of an electro-magnet, by causing the currents to alter the friction between the two rubbing surfaces, and so actuate a marker, which registered the message as in the Morse system.

This instrument was called the 'electromotograph,' and it occurred to Edison that in a similar way the undulatory currents from his carbon transmitter might, by varying the friction between a metal stylus and the prepared surface, put a tympanum in vibration, and reproduce the original sounds. Wonderful as it may appear, he succeeded in doing so by the aid of a piece of chalk, a bra.s.s pin, and a thin sheet or disc of mica. He attached the pin or stylus to the centre of the mica, and brought its point to bear on a cylindrical surface of prepared chalk.

The undulatory current from the line was pa.s.sed through the stylus and the chalk, while the latter was moved by turning a handle; and at every pulse of the electricity the friction between the pin and chalk was diminished, so that the stylus slipped upon its surface. The consequence was a vibration of the mica diaphragm to which the stylus was attached.

Thus the undulatory current was able to establish vibrations of the disc, which communicated themselves to the air and reproduced the original sounds. The replica was loud enough to be heard by a large audience, and by reducing the strength of the current it could be lowered to a feeble murmur. The combined transmitter and receiver took the form of a small case with a mouthpiece to speak into, an car-piece on a hinged bracket for listening to it, press-keys for manipulating the call-bell and battery, and a small handle by which to revolve the little chalk cylinder. This last feature was a practical drawback to the system, which was patented in 1877.

The Edison telephone, when at its best, could transmit all kinds of noises, gentle or harsh; it could lift up its voice and cry aloud, or sink it to a confidential whisper. There was a slight Punchinellian tw.a.n.g about its utterances, which, if it did not altogether disguise the individuality of the distant speaker, gave it the comicality of a clever parody, and to hear it singing a song, and quavering jauntily on the high notes, was irresistibly funny. Instrumental notes were given in all their purity, and, after the phonograph, there was nothing more magical in the whole range of science than to hear that fragment of common chalk distilling to the air the liquid melody of sweet bells jingling in tune.

It brought to mind that wonderful stone of Memnon, which responded to the rays of sunrise. It seemed to the listener that if the age of miracles was past that of marvels had arrived, and considering the simplicity of the materials, and the obscurity of its action, the loud-speaking telephone was one of the most astonishing of recent inventions.

After Professor Hughes had published his discovery of the microphone, Edison, recognising, perhaps, that it and the carbon transmitter were based on the same principle, and having learnt his knowledge of the world in the hard school of adversity, hastily claimed the microphone as a variety of his invention, but imprudently charged Professor Hughes and his friend, Mr. W. H. Preece, who had visited Edison at Menlo Park, with having 'stolen his thunder.' The imputation was indignantly denied, and it was obvious to all impartial electricians that Professor Hughes had arrived at his results by a path quite independent of the carbon transmitter, and discovered a great deal more than Edison had done. For one thing, Edison believed the action of his transmitter as due to a property of certain poor or 'semi-conductors,' whereby their electric resistance varied under pressure. Hughes taught us to understand that it was owing to a property of loose electrical contact between any two conductors.

The soft and springy b.u.t.ton of lamp-black became no longer necessary, since it was not so much the resistance of the material which varied as the resistance at the contacts of its parts and the platinum electrodes.

Two metals, or two pieces of hard carbon, or a piece of metal and a piece of hard carbon, were found to regulate the current in accordance with the vibrations of the voice. Edison therefore discarded the soft and fragile b.u.t.ton, replacing it by contacts of hard carbon and metal, in short, by a form of microphone. The carbon, or microphone transmitter, was found superior to the magneto-electric transmitter of Bell; but the latter was preferable as a receiver to the louder but less convenient chemical receiver of Edison, and the most successful telephonic system of the day is a combination of the microphone, or new carbon transmitter, with the Bell receiver.

The 'micro-tasimeter,' a delicate thermoscope, was constructed in 1878, and is the outcome of Edison's experiments with the carbon b.u.t.ton.

Knowing the latter to be extremely sensitive to minute changes of pressure, for example, those of sonorous vibrations, he conceived the idea of measuring radiant heat by causing it to elongate a thin bar or strip of metal or vulcanite, bearing at one end on the b.u.t.ton. To indicate the effect, he included a galvanometer in the circuit of the battery and the b.u.t.ton. The apparatus consisted of a telephone b.u.t.ton placed between two discs of platinum and connected in circuit with the battery and a sensitive galvanometer. The strip was supported so that one end bore upon the b.u.t.ton with a pressure which could be regulated by an adjustable screw at the other. The strip expanded or contracted when exposed to heat or cold, and thrust itself upon the b.u.t.ton more or less, thereby varying the electric current and deflecting the needle of the galvanometer to one side or the other. The instrument was said to indicate a change of temperature equivalent to one-millionth of a degree Fahrenheit. It was tested by Edison on the sun's corona during the eclipse observations of July 29, 1875, at Rawlings, in the territory of Wyoming. The trial was not satisfactory, however, for the apparatus was mounted on a hen-house, which trembled to the gale, and before he could get it properly adjusted the eclipse was over.

It is reported that on another trial the light from the star Arcturus, when focussed on the vulcanite, was capable of deflecting the needle of the galvanometer. When gelatine is subst.i.tuted for vulcanite, the humidity of the atmosphere can also be measured in the same way.

Edison's crowning discovery at Menlo Park was the celebrated 'phonograph,' or talking machine. It was first announced by one of his a.s.sistants in the pages of the SCIENTIFIC AMERICAN for 1878. The startling news created a general feeling of astonishment, mingled with incredulity or faith. People had indeed heard of the talking heads of antiquity, and seen the articulating machines of De Kempelen and Faber, with their artificial vocal organs and complicated levers, manipulated by an operator. But the phonograph was automatic, and returned the words which had been spoken into it by a purely mechanical mimicry. It captured and imprisoned the sounds as the photograph retained the images of light. The colours of Nature were lost in the photograph, but the phonograph was said to preserve the qualities even of the human voice.

Yet this wonderful appliance had neither tongue nor teeth, larynx nor pharynx. It appeared as simple as a coffee-mill. A vibrating diaphragm to collect the sounds, and a stylus to impress them on a sheet of tinfoil, were its essential parts. Looking on the record of the sound, one could see only the scoring of the stylus on the yielding surface of the metal, like the track of an Alpine traveller across the virgin snow.

These puzzling scratches were the foot-prints of the voice.

Speech is the most perfect utterance of man; but its powers are limited both in time and s.p.a.ce. The sounds of the voice are fleeting, and do not carry far; hence the invention of letters to record them, and of signals to extend their range. These twin lines of invention, continued through the ages, have in our own day reached their consummation. The smoke of the savage, the semaph.o.r.e, and the telegraph have ended in the telephone, by which the actual voice can speak to a distance; and now at length the clay tablet of the a.s.syrian, the wax of the ancient Greek, the papyrus of the Egyptian, and the modern printing-press have culminated in the phonograph, by which the living words can be preserved into the future. In the light of a new discovery, we are apt to wonder why our fathers were so blind as not to see it. When a new invention has been made, we ask ourselves, Why was it not thought of before? The discovery seems obvious, and the invention simple, after we know them.

Now that speech itself can be sent a thousand miles away, or heard a thousand years after, we discern in these achievements two goals toward which we have been making, and at which we should arrive some day. We marvel that we had no prescience of these, and that we did not attain to them sooner. Why has it taken so many generations to reach a foregone conclusion? Alas! they neither knew the conclusion nor the means of attaining to it. Man works from ignorance towards greater knowledge with very limited powers. His little circle of light is surrounded by a wall of darkness, which he strives to penetrate and lighten, now groping blindly on its verge, now advancing his taper light and peering forward; yet unable to go far, and even afraid to venture, in case he should be lost.

To the Infinite Intelligence which knows all that is hidden in that darkness, and all that man will discover therein, how poor a thing is the telephone or phonograph, how insignificant are all his 'great discoveries'! This thought should imbue a man of science with humility rather than with pride. Seen from another standpoint than his own, from without the circle of his labours, not from within, in looking back, not forward, even his most remarkable discovery is but the testimony of his own littleness. The veil of darkness only serves to keep these little powers at work. Men have sometimes a foreshadowing of what will come to pa.s.s without distinctly seeing it. In mechanical affairs, the notion of a telegraph is very old, and probably immemorial. Centuries ago the poet and philosopher entertained the idea of two persons far apart being able to correspond through the sympathetic property of the lodestone. The string or lovers' telephone was known to the Chinese, and even the electric telephone was thought about some years before it was invented.

Bourseul, Reis, and others preceded Graham Bell.

The phonograph was more of a surprise; but still it was no exception to the rule. Naturally, men and women had desired to preserve the accents as well as the lineaments of some beloved friend who had pa.s.sed away.

The Chinese have a legend of a mother whose voice was so beautiful that her children tried to store it in a bamboo cane, which was carefully sealed up. Long after she was dead the cane was opened, and her voice came out in all its sweetness, but was never heard again. A similar idea (which reminds us of Munchausen's trumpet) is found in the NATURAL MAGICK of John Baptista Porta, the celebrated Neapolitan philosopher, and published at London in 1658. He proposes to confine the sound of the voice in leaden pipes, such as are used for speaking through; and he goes on to say that 'if any man, as the words are spoken, shall stop the end of the pipe, and he that is at the other end shall do the like, the voice may be intercepted in the middle, and be shut up as in a prison, and when the mouth is opened, the voice will come forth as out of his mouth that spake it.... I am now upon trial of it. If before my book be printed the business take effect, I will set it down; if not, if G.o.d please, I shall write of it elsewhere.' Porta also refers to the speaking head of Albertus Magnus, whom, however, he discredits. He likewise mentions a colossal trumpeter of bra.s.s, stated to have been erected in some ancient cities, and describes a plan for making a kind of megaphone, 'wherewith we may hear many miles.'

In the VOYAGE A LA LUNE of De Cyrano Bergerac, published at Paris in 1650, and subsequently translated into English, there is a long account of a 'mechanical book' which spoke its contents to the listener. 'It was a book, indeed,' says Cyrano, 'but a strange and wonderful book, which had neither leaves nor letters,' and which instructed the Youth in their walks, so that they knew more than the Greybeards of Cyrano's country, and need never lack the company of all the great men living or dead to entertain them with living voices. Sir David Brewster surmised that a talking machine mould be invented before the end of the century. Mary Somerville, in her CONNECTION OF THE PHYSICAL SCIENCES, wrote some fifty years ago: 'It may be presumed that ultimately the utterances or p.r.o.nunciation of modern languages will be conveyed, not only to the eye, but also to the ear of posterity. Had the ancients possessed the means of transmitting such definite sounds, the civilised world must have responded in sympathetic notes at the distance of many ages.' In the MEMOIRES DU GEANT of M. Nadar, published in 1864, the author says: 'These last fifteen years I have amused myself in thinking there is nothing to prevent a man one of these days from finding a way to give us a daguerreotype of sound--the phonograph--something like a box in which melodies will be fixed and kept, as images are fixed in the dark chamber.' It is also on record that, before Edison had published his discovery to the world, M. Charles Cros deposited a sealed packet at the Academie des Sciences, Paris, giving an account of an invention similar to the phonograph.

Ignorance of the true nature of sound had prevented the introduction of such an instrument. But modern science, and in particular the invention of the telephone with its vibrating plate, had paved the way for it. The time was ripe, and Edison was the first to do it.

In spite of the unbridled fancies of the poets and the hints of ingenious writers, the announcement that a means of h.o.a.rding speech had been devised burst like a thunderclap upon the world.

[In seeing his mother's picture Byron wished that he might hear her voice. Tennyson exclaims, 'Oh for the touch of a vanished hand, and the sound of a voice that is still!' Sh.e.l.ley, in the WITCH OF ATLAS, wrote:

'The deep recesses of her odorous dwelling Were stored with magic treasures--sounds of air, Which had the power all spirits of compelling, Folded in cells of crystal silence there; Such as we hear in youth, and think the feeling Will never die--yet ere we are aware, The feeling and the sound are fled and gone, And the regret they leave remains alone.'

Again, in his SPIRIT OF SOLITUDE, we find: 'The fire of those soft orbs has ceased to burn, And silence too enamoured of that voice Locks its mute music in her rugged cell,']

The phonograph lay under the very eyes of Science, and yet she did not see it. The logograph had traced all the curves of speech with ink on paper; and it only remained to impress them on a solid surface in such a manner as to regulate the vibrations of an artificial tympanum or drum. Yet no professor of acoustics thought of this, and it was left to Edison, a telegraphic inventor, to show them what was lying at their feet.

Mere knowledge, uncombined in the imagination, does not bear fruit in new inventions. It is from the union of different facts that a new idea springs. A scholar is apt to be content with the acquisition of knowledge, which remains pa.s.sive in his mind. An inventor seizes upon fresh facts, and combines them with the old, which thereby become nascent. Through accident or premeditation he is able by uniting scattered thoughts to add a novel instrument to a domain of science with which he has little acquaintance. Nay, the lessons of experience and the scruples of intimate knowledge sometimes deter a master from attempting what the tyro, with the audacity of genius and the hardihood of ignorance, achieves. Theorists have been known to p.r.o.nounce against a promising invention which has afterwards been carried to success, and it is not improbable that if Edison had been an authority in acoustics he would never have invented the phonograph. It happened in this wise.

During the spring of 1877, he was trying a device for making a telegraph message, received on one line, automatically repeat itself along another line. This he did by embossing the Morse signals on the travelling paper instead of merely inking them, and then causing the paper to pa.s.s under the point of a stylus, which, by rising and falling in the indentations, opened and closed a sending key included in the circuit of the second line. In this way the received message transmitted itself further, without the aid of a telegraphist. Edison was running the cylinder which carried the embossed paper at a high speed one day, partly, as we are told, for amus.e.m.e.nt, and partly to test the rate at which a clerk could read a message. As the speed was raised, the paper gave out a humming rhythmic sound in pa.s.sing under the stylus. The separate signals of the message could no longer be distinguished by the ear, and the instrument seemed to be speaking in a language of its own, resembling 'human talk heard indistinctly.' Immediately it flashed on the inventor that if he could emboss the waves of speech upon the paper the words would be returned to him. To conceive was to execute, and it was but the work of an hour to provide a vibrating diaphragm or tympanum fitted with an indenting stylus, and adapt it to the apparatus. Paraffined paper was selected to receive the indentations, and subst.i.tuted for the Morse paper on the cylinder of the machine. On speaking to the tympanum, as the cylinder was revolved, a record of the vibrations was indented on the paper, and by re-pa.s.sing this under the indenting point an imperfect reproduction of the sounds was heard. Edison 'saw at once that the problem of registering human speech, so that it could be repeated by mechanical means as often as might he desired, was solved.' [T. A.

Edison, NORTH AMERICAN REVIEW, June, 1888; New York ELECTRICAL REVIEW, 1888,]

The experiment shows that it was partly by accident, and not by reasoning on theoretical knowledge, that the phonograph was discovered.

The sound resembling 'human talk heard indistinctly' seems to have suggested it to his mind. This was the germ which fell upon the soil prepared for it. Edison's thoughts had been dwelling on the telephone; he knew that a metal tympanum was capable of vibrating with all the delicacies of speech, and it occurred to him that if these vibrations could be impressed on a yielding material, as the Morse signals were embossed upon the paper, the indentations would reproduce the speech, just as the furrows of the paper reproduced the Morse signals. The tympanum vibrating in the curves of speech was instantly united in his imagination with the embossing stylus and the long and short indentations on the Morse paper; the idea of the phonograph flashed upon him. Many a one versed in acoustics would probably have been restrained by the practical difficulty of impressing the vibrations on a yielding material, and making them react upon the reproducing tympanum. But Edison, with that daring mastery over matter which is a characteristic of his mechanical genius, put it confidently to the test.

Soon after this experiment, a phonograph was constructed, in which a sheet of tinfoil was wrapped round a revolving barrel having a spiral groove cut in its surface to allow the point of the indenting stylus to sink into the yielding foil as it was thrust up and down by the vibrating tympanum. This apparatus--the first phonograph--was published to the world in 1878, and created a universal sensation. [SCIENTIFIC AMERICAN, March 30, 1878] It is now in the South Kensington Museum, to which it was presented by the inventor.

The phonograph was first publicly exhibited in England at a meeting of the Society of Telegraph Engineers, where its performances filled the audience with astonishment and delight. A greeting from Edison to his electrical brethren across the Atlantic had been impressed on the tinfoil, and was spoken by the machine. Needless to say, the voice of the inventor, however imperfectly reproduced, was hailed with great enthusiasm, which those who witnessed will long remember. In this machine, the barrel was fitted with a crank, and rotated by handle. A heavy flywheel was attached to give it uniformity of motion. A sheet of tinfoil formed the record, and the delivery could be heard by a roomful of people. But articulation was sacrificed at the expense of loudness.

It was as though a parrot or a punchinello spoke, and sentences which were unexpected could not be understood. Clearly, if the phonograph were to become a practical instrument, it required to be much improved.

Nevertheless this apparatus sufficiently demonstrated the feasibility of storing up and reproducing speech, music, and other sounds. Numbers of them were made, and exhibited to admiring audiences, by license, and never failed to elicit both amus.e.m.e.nt and applause. To show how striking were its effects, and how surprising, even to scientific men, it may be mentioned that a certain learned SAVANT, on hearing it at a SEANCE of the Academie des Sciences, Paris, protested that it was a fraud, a piece of trickery or ventriloquism, and would not be convinced.

After 1878 Edison became too much engaged with the development of the electric light to give much attention to the phonograph, which, however, was not entirely overlooked. His laboratory at Menlo Park, New Jersey, where the original experiments were made, was turned into a factory for making electric light machinery, and Edison removed to New York until his new laboratory at Orange, New Jersey, was completed. Of late he has occupied the latter premises, and improved the phonograph so far that it is now a serviceable instrument. In one of his 1878 patents, the use of wax to take the records in place of tinfoil is indicated, and it is chiefly to the adoption of this material that the success of the 'perfected phonograph' is due. Wax is also employed in the 'graphophone'

of Mr. Tainter and Professor Bell, which is merely a phonograph under another name. Numerous experiments have been made by Edison to find the bees-wax which is best adapted to receive the record, and he has recently discovered a new material or mixture which is stated to yield better results than white wax.

The wax is moulded into the form of a tube or hollow cylinder, usually 4 1/4 inches long by 2 inches in diameter, and 1/8 inch thick. Such a size is capable of taking a thousand words on its surface along a delicate spiral trace; and by paring off one record after another can be used fifteen times. There are a hundred or more lines of the trace in the width of an inch, and they are hardly visible to the naked eye. Only with a magnifying gla.s.s can the undulations caused by the vibrating stylus be distinguished. This tube of wax is filed upon a metal barrel like a sleeve, and the barrel, which forms part of a horizontal spindle, is rotated by means of a silent electro-motor, controlled by a very sensitive governor. A motion of translation is also given to the barrel as it revolves, so that the marking stylus held over it describes a spiral path upon its surface. In front of the wax two small metal tympanums are supported, each carrying a fine needle point or stylus on its under centre. One of these is the recording diaphragm, which prints the sounds in the first place; the other is the reproducing diaphragm, which emits the sounds recorded on the wax. They are used, one at a time, as the machine is required, to take down or to render back a phonographic message.

The recording tympanum, which is about the size of a crown-piece, is fitted with a mouthpiece, and when it is desired to record a sentence the spindle is started, and you speak into the mouthpiece. The tympanum vibrates under your voice, and the stylus, partaking of its motion, digs into the yielding surface of the wax which moves beneath, and leaves a tiny furrow to mark its pa.s.sage. This is the sonorous record which, on being pa.s.sed under the stylus of the reproducing tympanum, will cause it to give out a faithful copy of the original speech. A flexible india-rubber tube, branching into two ear-pieces, conveys the sound emitted by the reproducing diaphragm to the ears. This trumpet is used for privacy and loudness; but it may be replaced by a conical funnel inserted by its small end over the diaphragm, which thereby utters its message aloud. It is on this plan that Edison has now constructed a phonograph which delivers its reproduction to a roomful of people.

Keys and pedals are provided with which to stop the apparatus either in recording or receiving, and in the latter case to hark back and repeat a word or sentence if required. This is a convenient arrangement in using the phonograph for correspondence or dictation. Each instrument, as we have seen, can be employed for receiving as well as recording; and as all are made to one pattern, a phonogram coming from any one, in any art of the world, can be reproduced in any other instrument. A little box with double walls has been introduced for transmitting the phonograms by post. A knife or cutter is attached to the instrument for the purpose of paring off an old message, and preparing a fresh surface of the wax for the reception of a new one. This can be done in advance while the new record is being made, so that no time is lost in the operation. A small voltaic battery, placed under the machine, serves to work the electric motor, and has to be replenished from time to time. A process has also been devised for making copies of the phonograms in metal by electro-deposition, so as to produce permanent records. But even the wax phonogram may be used over and over again, hundreds of times, without diminishing the fidelity of the reproduction.

The entire phonograph is shown in our figure. [The figure is omitted from this e-text] It consists of a box, B, containing the silent electro-motor which drives the machine, and supporting the works for printing and reproducing the sounds. Apart from the motive power, which might, as in the graphophone, be supplied by foot, the apparatus is purely mechanical, the parts acting with smoothness and precision. These are, chiefly, the barrel or cylinder, C, on which the hollow wax is placed; the spindle, S, which revolves the cylinder and wax; and the two tympana, T, T', which receive the sounds and impress them on the soft surface of the wax. A governor, G, regulates the movement of the spindle; and there are other ingenious devices for starting and stopping the apparatus. The tympanum T is that which is used for recording the sounds, and M is a mouthpiece, which is fixed to it for speaking purposes. The other tympanum, T', reproduces the sounds; and E E is a branched ear-piece, conveying them to the two ears of the listener. The separate wax tube, P, is a phonogram with the spiral trace of the sounds already printed on its surface, and ready for posting.

The box below the table contains the voltaic battery which actuates the electro-motor. A machine which aims at recording and reproducing actual speech or music is, of course, capable of infinite refinement, and Edison is still at work improving the instrument, but even now it is substantially perfected.

Phonographs have arrived in London, and through the kindness of Mr.

Edison and his English representative, Colonel G. E. Gouraud, we have had an opportunity of testing one. A number of phonograms, taken in Edison's laboratory, were sent over with the instruments, and several of them were caused to deliver in our hearing the sounds which were

'sealed in crystal silence there.'

The first was a piece which had been played on the piano, quick time, and the fidelity and loudness with which it was delivered by the hearing tube was fairly astonishing, especially when one considered the frail and hair-like trace upon the wax which had excited it. There seemed to be something magical in the effect, which issued, as it were, from the machine itself. Then followed a cornet solo, concert piece of cornet, violin, and piano, and a very beautiful duet of cornet and piano. The tones and cadences were admirably rendered, and the ear could also faintly distinguish the noises of the laboratory. Speaking was represented by a phonogram containing a dialogue between Mr. Edison and Colonel Gouraud which had been imprinted some three weeks before in America. With this we could hear the inventor addressing his old friend, and telling him to correspond entirely with the phonograph. Colonel Gouraud answers that he will be delighted to do so, and be spared the trouble of writing; while Edison rejoins that he also will be glad to escape the pains of reading the gallant colonel's letters. The sally is greeted with a laugh, which is also faithfully rendered.