"iu -^^K ^^\^. IMAGE EVALUATION TEST TARGET (MT-3) y y. ^ 1.0 I.I l;;|28 |2.5 i^i 1^ |||2.2 m It lifi IIIIIM 1.8 - 6" 11.25 III 1.4 ill 1.6 V] Si . :ri' ■ OlIAlTKlt. PaOK. 1. — Tlio Si)eiikiiij5 Ti'lcpIioMO fi II. — Bell's 'rclupliDiiic Hcsciirclios 00 1 II. — The TcIcplioiK' Abroiul 8;i ]V. — History of tlic Produotiou of Galvanic Music 110 V. — Oniy'.s Telephonic Koscarchcs ISl VI. — •Kdison'.y Telephonic Re-Jearclics '218 VII. — Kloctro-llarnionic Telojii-apliy '235 VI n. — Dolbear's Telephonic Reseaiclics '2G0 L\. — Iniprovcmcnts of Channinj;. Bluku and oilu-rs 2'i .\,— The Talking Phouograph 292 X I. — Quadrnplox Telegraphy •*"'' XII. — Kloctric, Call Bolls :"5 XIII.— The Kloctric Light ^'lO Up( tliii V(-!' tha U)v \ out Slip gr;ij by froii trll botv decc tho obsc tho Ii defle INTR()r)ITCTIO:N" A WllKX H'niiiklin dnw I'imip. the clouds iIh; chjctric! spark iipoii tilt! cord of liis kite, it scciiicd oiivioiis that electricity Miiglit be luadc use of I'or the piirposi; of telegnipliy; and more than one hundred years ago Lesagc; estul)lisliod a teh^graph in (lencva by tlu- use of frietionai clecrtrieity. Hut tliis force had very litll( power when transmitted over a long distance, and that little was |n'aetieally uneontnjlhihle, and therefore useless ior telegraphy. When galvanism was discovered, at the bcgiimingof the pres- ent century, and tlu; voltjiie battery invented, it was at once su[)p()scd that this new form of electricity might work a tele- graph, and ten years later the chemical telegraph was invented l^y Coxe, in Philadel])hia. Under this system, the two wires from a galvanic battery were made to approach each other in a ci'll of water. When the galvanic circuit was closed, the water iK-lwecn the ojiiKjsite poles, which were near each other, was decomposed, and a bubble of hydrogen rose to the surface, as the bubble from champagne does in the wine cup; and the observer, seeing it, knew that a current was passing, and that the bubble was the signal. But it was evanescent " like snow fall.s in tlio livor, A iiLinicnt wliite, tlicn meltH forovor.'.' In 1820, Oei-stcd discovered that an electric current would deflect a magnetic needle, and Arago aad Davy simultaneously u INTUODUCTION. (liscovon'il that u piece of irmi, suiToiimled ]>y a spiral wirn tlimilgli wliieli ii. eiiiTeiil of ;jiilviiiiism piisscd, would heeonie iiuigiietic. From this fact Ampere dedu 1 the liypotiiesis that in.'igiictism in tlie circidatinu of ciirreiits of electricity nt right angles ti) the axis joining the two poles of the iiiagnot. That was a hrilliaiit deduction: Imt no [)raetieai resn.t was produced from it until lS2r), when iIk^ first sim[il(! el(>(on a ])i'rnian(Mit magnet, around wliich it was placed. Tho slow oscillations of a magnetic needle, caused hv th(! passage of the ciu'rent, and whicli were ol)scrved throngli a glass, furnished the signals for eorrcspoiidenee. Sir William Thomson has since greatly improveil tho latter appa- ratus, and thereby given us the licautifuUy sensitive mirror gal- vanometer which bears his minic. In 1837, Stcinheil di.M-overcil the important fact that the eartli would serve as a conductor, thereby saving oiu- wire in forming a circuit: Cook*^ invented his electro-magnetic semaphore, known as the needle telegraph, in which nees is distin- guished at the other, and yon hear them all as if you stood in their prcsenee. That is th(> erowniiiLC aehicvement of the eleetro- magnctic telegraph. Thi.s beautiful thing — thi.s mysterious telegraj)!) — l>eginning awav off a century ago, and now so developed that man can speak to his fello\\-man at the distance of hundreds of miles, as though they were face to face, and can h(>ar the tones of tlie familiar A^oice, and the loved accent, of him whom he would Avish to greet — that beautiful thing has been created by the genius and the eflorts of numbers of oui' fellow-men, whose names ought to be remembered now. Franklin, Oersted, Arago, Amii6re, Davy, Sturgeon, Ilein-y, Page and Gray (who also in- vented the iir.st articulating telephone), are they who made the great u;'-coverie.s, and added to theti'ea.sury of human knowledge the truths upon which these wonderful and beautiful results are jiroduccd. Passing by them, and coming to ihc men who made the new combinatiouH <;f mechanical devices, to utilize those discoveries, w(^ have in order — Morse, Cooke, Steiidieil, lieiss, Stearns, Edison, Bell, Dolbear — all names worthy t)f lienor and respect. '^^IMie first arc investigators in .science, who have discovered new trutlus — who have ascended from nature to nature's God — who have traced out some of the secret links that bind together liumanity an(i the Supreme Being in one common chain ; the others are men who have, by their ingcnuit}' and mechanical skill, developed these discoveries into usefulne,s.s, niniv jiiiil more perfect, for man. Let us think of them, and be thankful to them, for what tluy have done for u.s. Then- names are for ever as,soeiated witli this izreat art, under which VI IXTKODUCTION. SO much advance has been made in civilization, in refinement, and in love among men — so much has been done to dispel the dark clouds of war from earth, and make us all one oonimon family — the brotherhood of man. Along the amootli and slender wires The sleepless lieridds run, Fast as tlio clear and living riiys Go streaming from the sun. No peals or flashes, heard or seen, Their wondrous flight betray; But yet their words are quickly felt In cities far away. Nor summer's heat, nor winter's cold. Can check their rapid course ; Unmoved tlicy meet the fierce v.-ind's Ijlast — The rough waves' sweeping force. In the long night of rain and wratli. As in the blaze of day, Tlioy rusli, with news nf weal or woo To thousands far away. '^. CHAPTER! H.M,Pomeroy,M,D. THE SPEAKIxa TELEl'HON*li:°^ Angeles, Cal. The Speaking Telephone, a recent American invention, which at the present moment is exciting the wonder and admiration of the civilized world, is a device for transmitting to a distance, over an electric circuit, and accurately reproducing at any desired place, various kinds of sounds, including those of the human voice. The function of the telephone is analogous to that of a speaking tube capable of almost infinite extension, through which conversation may be carried on as readily as with per- sons in the same room. Before proceeding to give a description of the apparatus employed for communicating or reproducing articulate sjieech at a distance by the telephone, it will be well to devote some con- sideration to the process by which the ear distinguishes the vibra- tions of a particular tone, or the aggregate of the vibrations of all the tones which simultaneously act upon it, for by this means we may be enabled to ascertain the conditions under which the transmitting and receiving apparatus must act in order to effect the desired result. It is well known that the sensation which we call sound is excited by the action of the vibrations of the atmosphere upon the tympanum or drum of the ear, and that these vibrations are conveyed from the tympanum to the auricular nerves in the interior parts of the ear, by means of a mechanical apparatus of wonderful delicacy and precision of action, consisting of a series ot" bones termed respectively the hammer, anvil and stirrup. In the process of reproducing tones by electro-magnetism, an arti- ficial imitation of the mechanism of the human ear is emi)loyed, consisting of a stretched membrane or diaphragm corresponding to the tympanum, which by its vibrations generates and controls 6 THE SPEAKIXG TELKPHONE. an electric circuit extended lo ii distant station by a, metallic conductor. If we analyze the process by which the ear distinguishes a simple sound, we find that a tone results from the alternate ex- pansion and condensation of an clastic medium. If this jirocess takes place in the medium in which the car is situated, namely, the atmosphere, then at each recurring condensation the elastic membrane or tymjianum will be pressed inward, and these vibra- tions will be transmitted, by the mechanism above referred to, to the auricular nerves. The greater the degree of condensation of the elastic medium in a given time, the greater is the amplitude of the movement of the tympanum, and consequently of the mcclianism which acts v.pon the nerves. He:.ce it follows that the function of the human ear is the mechanical transmission to the auditory nerves of each expansion and contraction which occiu's in the surround- ing medium, while that of the nerves is to convey to the brain the sensations thus produced. A scries of vibrations, a detinite number of ■v. iiich are produced in a given time, and of which we thus become cognizant, is called a tone. The action which has thus reached our consciousness, being a purely mechanical one, may be rendered much more easy of comprehension by graphical delineation. If, for example, we assume the horizontal line a h to represent a certain period of time, let the curves extending above the line (f h rejiresent the successive condensations ( -f- ), nnd the ciu'ves below the lino the successive expansions ( — ), then each ordinate represents the degree of condensation or expansion at tlie moment of time cor- responding to its position upon the linea // and also the amplitude of the vibrations of the tympanum. A simple musical tone results from a continuous, rapid and uniformly recurring series of vibrations, provided the number of THE CHARACTERISTICS OF SOfND. 7 complete vibrations per second falls within certain limits. If, lor example, the vibrations number less than seven or eight per second, a series of successive noises are heard instead of a tone, while if their number exceeds forty thousand per second, the ear becomes incapable of appreciating the sound. The ear distinguishes three distinct characteristics of sound : 1. The tone or pitch, by virtue of whicli sounds are high or low, and which depends upon the rapidity of the vilmatory move- ment The more rapid the vibrations the more acute will bo the sound. 2. The intensity, by virtue of which sounds are loud or soft, and which depends upon the amplitude of the vibrations. 3. The quality, by which we are able to distinguish a note sounded upon, for example, a violin, from the same note when sounded upon a flute. By a remarkable series of experi- mental investigations Ilelmholtz succeeded in demonstrating that the different qualities of sounds depend altogether upon the number and intensity of the overtones which accompany the primary tones of those sounds. The different characteristics of sound may be graphically represented and the phenomena thus rendered more easy of comprehension. In lig. 1, for example, let the lines c 8 represent a certain length of time, and the continuous curved line the successive vibrations producing a simple tone. The curves above the line represent the compression of the air, and those below the line its rarefaction ; the air, an elastic medium, is thus thrown into vibrations which transmit the sound waves to the ear. The ear is unable to appreoiai. any sensations of sound other than those produced by vibrations, which may be represented by curves similar to that above described. Even if several tones are pro- duced simultaneously, the elastic medium of transmission is under the influence of several forces acting at the san.e time, and which are subject to the ordinary laws of mechanics. If the diff'irent forces act in the same direction the total force is rep- resented by their sum, while if they act in opposite directions, it is represented by the difference between them. 8 THE SPEAKING TELEPHONE. Ill fig. 1 three distinct simple tones, c, g and e are represented, the rapidity of the vibrations being in the proportion of 8, 6 and 5. The composite tone resulting from the simultaneous pro- duction of the tln-ee simple tones is represented graphically by the fourth line, which correctly exhibits to the eye the effect pro- Pigs. ^, 2, 3. duced u})on tlie ear by the three simultaneously acting simple tones. Fig. 2 represents a curve formed of more than three tones, in which the relations do not appear so distinctly, but a musical ItEISSS MUSIOAL TELEPHONE. 9 expert will readily recognize them, even when it would be diffi- cult in practice for him to distinguish the simple tones in such a chord. This method of showing the action of tones u[)on the human ear possesses the advantage of giving the clearest illustration possible of the entire process. We may even understand by reference to fig. 3 why it is that the car is so disagreeably affected by a discord. It will be observed that the curves in the diagram represent the three characteristics of sound which have been referred to. The pitch is denoted by the number of vibrations or waves re- curring within a given horizontal distance ; the intensity by the amj^litudc of the vibrations — that is their comparative height above or depth below the horizontal line — and the quality I'y the form of the waves themselves. It is, therefore, easy to understand that if, by any means whatever, we can pro- duce viVjrations whose curves correspond to those of a giv'^ tone or a given combination of tones, the same impression will be produced upon the ear that would have been produced by the original tone, whether simple or composita The earliest experiments in the production of musical sounds at a distance, by means of electro-magnetism, appear to have been made in 1861 by Philip Reiss, of Friedrichsdorf, Germany. Ilis apparatus was constructed in the manner shown in fig. 4. A is the transmitting and B the receiving apparatus, which arc supposed to be situated at different stations. For the sake of clearness, the appliances by which the apparatus is arranged for reciprocal transmission in one direction or the other have been omitted. Furthermore, it may be well to state that, as the ap- paratus was constructed merely for tlie purpose of making known to a wider circle the discoveries which had thus flxr been made, the possibility of extending the action of the apparatus to a dis- tance beyond the limit of the direct action of the current had not been taken into consideration. This is a mere question of me- chanical construction, and has no especial bearing upon the phe- nomena under consideration. The tone transmitter A, figure 4, 10 THE SPEAKING TELEI'HONK. is on tlio ono liand coniiectnd bj a metallic conductor with the tone receiver 15 at the distant station, and on the other with the battery C' and the earth, or the return conductor. It consists of a conical tube, a b, about 6 inches in length, and having a di- ameter of 4 inches at the larger and 1^ inches at the smaller end. HEISS.S MUSICATi TELEPnONK. 11 with tlie witli the onsists of r laving a di- maller end. It, was found by experiment that the material of wliich the tube was constructed had no influence upon tlie action of the appa- ratus, and the same is true as to its lengtli. An increase in the diameter of the tube was found to impair the elFect, The inner surface of the tube should be made as smootli as possible. The smaller or rear end of the tube ia closed by means of a collodion membrane, o, against the centre of wliich rests one extremity, c, of the lever c d, which lever is in electrical connection with the metallic conducting wire through its point e and supporting bracket. The proper length and proportion to be given to the respective arms c o and rf e of the lever c e d ia determined by mechanical considerations. It is advisable that the length of the arm c e should be greater than that of d e, so as to produce the necessary movement at c with the least possible exertion of force at d. The lever itself should be made as light as possible, in order that it may follow with certainty the movements of the membrane, as any inaccuracy in tliis respect will give rise to a false tone at the receiving station. When the apparatus is in a state of rest the contact at d ^ is closed ; a delicate spring n maintains the lever in this j^osition. The metallic standard / is connected with one pole of the battery C, the other pole of which is connected to the earth, or to the return wire leading to the other station. A flat si)ring g is attached to the standard f, and is provided with a contact point corresponding to that at d upon the lever c d. The position of this contact point may be adjusted by means of a screw h. In order to prevent the interference occasioned by the action of the sonorous vibrations of the atmosphere upon the back side of the membrane, when making use of the apparatus, it is advis- able to place a disk about twenty inches in diameter upon the tube o b, in the form of a collar or flange, at right angles to its longitudinal axis. The tone receiver B, fig. 4, consists of an electro-magnet m, mounted upon a sounding box or resonator lo, and included in tlie circuit of the electrical conductor from the transmitting station. Facing the poles of the electro-magnet is an armature 12 THE SPEAKING TELEPHONE. which is attached to a broad but thin and light plate, i, which should be made as long as possible. The lever and armature are suspended from the upright support k, in the manner of a pendulum, its motion being regulated by tlie adjusting screw I and the spring a. In order to increase the volume of sound, the tone receiver may be placed at one of the focal points of an elliptical chamber of suitable size, while the ear of the listener is placed at the other focal point The operation of the apparatus is as follows : When the different parts are in a state of rest the electric circuit is closed. If an alternate condensation and rarefaction of the air in the tube a 6 is produced by speaking, singing, or playing upon a musical instrument, a corresponding motion is communicaied to the membrane, and from thence to the lever e d, by which means the electric circuit is alternately opened and closed at d g, each condensation of the air in the tube causing the circuit to be broken, and each rarefaction in like manner causing it to be closed. Thus the electro-magnet m m, of the apparatus at B, becomes demagnetized or magnetized, according to the alternate condensations and rarefactions of the body of air contained in the tube a b, and consequently the armature of the electro-mag- net is thrown into vibrations corresponding to those of the mem- brane in the transmitting apparatus. The plate t, to which the armature is attached, transmits the vibrations of the latter to the surrounding atmosphere, which in turn conveys them to the ear of tlie listener. It must however le admitted, that while the apparatus which has been described re^Toduces the original vibrations with per- fect fidelity, so far as thei- number and interval is concerned, it cannot transmit their intensity or amplitude. The accomplish- ment of this latter result had to await the further development of the invention. It was in consequence of this defect in the apparatus that the more inconsiderable differences of the original vibrations were distinguished with great difficulty — that is to say, the vowel HKI3SS MUSrCAIi TELEPirONK 18 sounds were heard with moro or loss iiidisiiiictness, for the reason that tho character of each tone depends not merely upon the number of tho sonorous vibrations, but upon their intensity or amplitude also. Tins also accounts for tho observed fact that while chords and melodies were transmitted and reproduced with a surprising degree of accuracy, single words, as pronounced in reading or speaking, were but indistinctly heard, althougli in this case, also, tho infl i.tionsof the voice, interrogative, exclama- tory, etc., could be distinguished without difficulty. Figure 5 illustrates another form of Reiss's apparatus. A is a hollcnv wooden box, provided with two apertures, one at tlie top and tlio other iu front The former is covered with a membrane S, such as a piece of bladder, tightly stretched in a Fig. 5. circular frame. When a person sings into the mouthpiece Af, which is inserted in the front opening, the whole force of his voice is concentrated on tho tight membrane, which is thrown into vibrations corresponding exactly with tho vibrations of tho air produced by the sound of the singing. A thin piece of pla- tinum is glued to the '^entre of the membrane and connected with the binding screw a, in whicli a wire from the battery B is fixed. Upon the membrane rests a little tripod c fg, of which tlic feet e and /rest in metal cups upon the cu'cular frame over which the skin is stretched. One of them, J\ rests in a mer- cury cup connected with tho binding screw h. The third foot, r/, consisting of a platinum contact point, lies on the strip of plati- u TilK SPEAKING TELKl'HONK. iiiim wliich is plncod upon tlio ccntro of tlm vibrating mrmhrnne ami hops up and down with it. By this inoans tiiu closed circiiii which passes tlirough tho aj)paratus from B or from B to A, depends simply upon the direction of the motion of n 5. 18 THE SPEAKING TELEPHONE. The electricity thus generated in the wire by such vibratory movements varies in strength, as already observed, with the variations in the movement of the armature ; the line wire be- tween two places will, therefore, be filled with electrical pulsa- tions exactly like the atrial pulsations in structure. These induced electric currents are very trnnsient, and their effect upon the receiver R is either to increase or decrease the power of the magnet there, as they are in one direction or the other, and consequently to vary the nttractive power exercised upon the iron plate armature. Let a simple sound be made in the tube, consisting of 256 vibrations per second ; the membrane carrying the iron will vibrate as many times, and so many pulses of induced elec- tricity will be imposed upon the constant current, which will each act upon the receiver, and cause so many vibrations of the armature upon it; and an ear held near /• will hear the sound with the same pitch as that at the sending instrument If two or more sound waves act simultaneously upon the membrane, its motions must correspond with such combined motion ; that is, its motion will be the resultant of all the sound waves, and the corresponding pulsations in the current must reproduce at B the same eflect. Now, when a person speaks in the tube, the membrane is thrown into vibrations more complex in structure than those just mentioneil, differing only in number and inten- sity. The magnet will cause responses from even the minut- est motion, and, therefore, an ear near r will hear what is said in the tube. Consequently, this apparatus is capable of transmitting ^:Dth the pitch and intensity of the tones which enter the tube T. The receiving instrument consists simply of a tubular electro-magnet R, formed of a single helix with an ex- ternal soft iron casi', into the top of whif;h is loosely fitted the iron plate r, which is thrown into vibrations by the action of the magnetizing helix. The sounds produced in this manne were quite weak, and could be transmitted but a short distance ; but the mere accomplisiiment of the feat of transmitting electric impulses over a metallic wire which should reproduce articu- DOLBEARS SPKAKING TELEPHONE. 19 late speech, even in an imperfect manner, at the farther end, ex- cited great interest in a scientific as well as jiopular point of view, throughout the civilized world. During the ensuing autumn some important changes in the telephone were effected, wherel)y its articulating properties were greatly improved. Professor A. E. Dolbear, of Tufts Col- lege, observing that the actual function of the battery current with which the line was charged in Bell's method had simply the effect oi polarizing the soft iron cores of the transmitting and receiving instruments, or of converting them into permanent magnets, and that the mere passage of the constant voltaic cur- rent over the line had nothing to do with the result, conceived the idea of maintaining the cores in a permanently magnetic or polarized state by the inductive influence of a permanent mag- ^ net instead of by a voltaic current. He therefore substituted ])crmanent magnets with small helices of insulated copper wire surrounding one or both poles, in place of the electro-magnets and battery previously employed. Another important improvement made by him consisted in using the same instrument for botli sending and receiving instead of employing instruments of different construction, as all previous inventors han done. The principle and mode of operation of the improved appara- tus is represented in figure 8. It consists of an ordinary permanent bar magnet, N S, a single helix, n, of insulated copper wire placed upon one end of the magnet, and a metallic diaphragm, D, consisting of a disk of thin 20 THE SPEAKING TELEPHONE. sheet iron, two and a quarter inches in diiimctcr and one fiftieth of an inch thick, forming an armature to the magnet, N S. The vibratory motions of the air produced by the voice or other cause are directed towards and concentratctl u})ou the diaphragm, D, by means of a mouthpiece, T. It will thus be seen that when vibrations are communicated to the air in front of the mouth- piece the impact of the waves of air against the elastic dia{>lu'agm will cause a corresponding movement of the latter. This in turn, by reacting upon the magnet, disturbs the normal magnetic con- dition of the bar, and since any change of magnetism in this tends to generate electrical currents in the surrounding helix, the circuit in which the helix may be placed will be traversed by a series of electrical pulsations or currents. Moreover, as these currents continue to be generated to long as the niotion of the diaphragm continues, and as they increase and decrease in strength with the amplitude of its vibrations, thus varying with the variations of its amplitude, it is evident that they virtually possess all the physical characteristics of the agent acting upon the transmitting diaphragm. Consequently, by their electro- magnetic action upon the magnet of an apparatus identical with the one above described, and placed in the same circuit at the receiving end, they will cause its diaphragm to vibrate in exact correspondence with that of the transmitting apparatus. ' During the past year many ingenious persons have turned their attention to the subject of telephones, and by the introduction of various modifications have succeeded in greatly improving the invention, so as to make it available for practical applica- tion. Prominent among these is ^fr. G. M. Phelps, mechunician of the Western Union Telegraph Company, to whose ability in the invention of valuable improvements, as well as in the scien- tific arrangement of details in tlie construction of the apparatus, the public is indebted for some of the most eflective telephones yet introduced. Tiie peculiar excellence of these instruments consists in their distinct articulation, combined with a loudness of utterance that is not often met with in the numerous other forms that have appeared up to the present time. Both of these PHELPS S DUPLEX TELEPHONE, 21 qualities, manifestly so desirable, are developed in these instru- ments in a very remarkable degree, while the distance over which they may be used is also another of their distinguishing charac- teristics, circuits of over one hundred miles having been worked by them with the most admirable results. The most essential improvements introduced by Mr. Phelps consist in combining two or more vibrating diaphragms and two or more corresponding magnetic cores, enveloped in separate helices, connected in the same circuit, with a single mouthpiece or vocalizing chamber ; in mounting two magnetic cores, when combined with separate diaphragms and coils, and a single mouthpiece, upon opposite poles of the same permanent magnet, ami in subdividing a single continuous induction plate into two or more separate and distinct areas of vibration, thus virtually forming two or more separate diaphragms, each of which acts or is acted ui)ou b\' a separate magnetic core, to the conseciuent in- creased usefulness of the apparatus. Figure 9 represents a form of the instrument constructed upon the above principles, which, both as regards distinctness of articulation and the facility with which it permits conversation to be carried on in consequence of the loudness of its tone, leaves little else to be desired. It consists of the permanent magnet M of hardened steel, which is bent into an oblong form, so as to occii|iy but little space, and also bring its poles conveniently near each other ; two helices, 11 and II', of copper wire, placed respectively upon the north and south poles of the magnet; two 22 THE SPEAKING TELEPUONE. metallic diaphragms, D and D*, and the speiiking tube or mouth- piece T, which may be made of wood, metal, or suoh other substance as fancy may suggest. The diaphrngms are placed upon opposite sides of a short cylindrical piece of hard rubber, provided with a lateral opening for the insertion of the mouth- piece, and, together with it, form a sort of chamber, within which the air is alternately condensed and rarefied, in conse- quence of the motion or impulses communicated to its particles by the voice when directed toward the opening of the tube. Hence, it will be seen that each condensation exerts an outward pressure of its own upon the diaphragm, while ench rarefaction causes a corresponding pressure from the external air, and thus a vibratory movement is imparted to both diaphragms at one and the same instant ; consequently, if the helices are so con- nected that the direction of the current pulsations, which are inductively produced by the vibrations of the diaphragms in the raanner already explained, are similar when they become united in the line, the magnetic force, as exhibited in the receiving ap- paratus at the distant station, will be augmented considerably above that produced by the action of a single coil and diaphragm alone, and thereby a corresponding increase in the loudness of the sound will be produced. The besteirocts are obtained when instruments of this form are employed both in transmitting and receiving, the advantages they possess for the latter purpose being quite as marked as for the former, as will appear obvious enough when we consider that every time a current p:\s.«es through the helices tlie attractive forces thereby imparted to the cores or magnet poles are such as to cause the centres of the two diaphragms to be drawn directly from eacli other, thus produc- ing a "" 'ch greater rarefaction of the air within the chamber than ^^ald be obtained by the action of a single diaphragm alone. A corresponding condensation, on tlic other hand, is pro- duced at each cessation of tlie current, owing to the return of the diaphragms, in virtue of their elasticity to their normal position. The greater the degree of condensation and rarefaction, how- ever, the greater the amplitude of tlie sonorous vibrations — one PHELPS S DUPLEX TELEPHONE. 23 •r mouth- loli other re placed 1 rubber, le mouth- :r, within in conse- ! particles the tube. I outward arefaction and thus ;ras at one re so con- which are ^ms in the irne united leiving ap- tisidcrably liaphragm oudness of ,ined when litting and !r purpose ar obvious ent p;\s.«es rted to the of the two us produc- le chamber diaphragm and, is pro- turn of the al position, ction, how- itions — one expression being the equivalent of the other — and, therefore, the <'-reater will be the intensity or loudness of the sound produced. We might add, in this connection, that the introduction of a second helix in the lino circuits presents in itself a slight disad- vantage. This arises from the inductive action of the pulsatory currents upon themselves in the coils and the reactive influence of the core, wliereby other and opposing currents are produced, which tend to delay, and, in part, neutralize the effects of the former. The latter are termed extra currents, to distinguish them from those produced in circuits exterior to that in which Fi^j. 10. tlie inducing currents are passing. As tlicy are found to accom- pany all electro-magnetic action whenever one i)art of a circuit is brought in proximity to another, as is the ca-^e in magnet helices, it will readily be seen that they must become the more troublesome as the number of stations are increased — it being necessary to keep the vibratory bells at eacli station in cir- euits, in order that calls may be heard. By the use of con- densers, consisting of alternate sheets of tin foil and paraffined yiaper jilaeed around tlic bell coils, we are enabled to overcome the difficulty these currents would otherwise present. Con- 24 THK SPKAKING TELEPHONE. dcnsers, therefore, hccoino ahnosL indispensable in cases where many telephones are employed iu one circuit. The instrument we have just described is made separate by itself, to be used as a transmitting or receiving instrument, or it is combined in a box represented below, with a call bell and the oval shaped telephone to be consii^ered presently. In the latter case it is usually employed to transmit alone, while the oval form serves for receiving ; it can, however, be used for either purpose. Fiij. n. Mr. Phelps also found that the cllicieucy of tlic telephone for transmitting tlio human voice was iimeh improviMl by reducing the cavity or chamber in which the diaphragm vibrates to tlie smallest practicable dimensions. Further gain was also made by cushioning the bearings of the diaphragm on both sides with rings of paper. In the for;n described below t!ie diaphragms are still further cushiuned on the .side towards the mauinets by a O.Xtl repi ofh nee <'011 I'UKLPS'S DLTLEX TKLKPHONK. 25 es where )arjite by jnt, or it I and tbe the latter 3val form • purpose. cphouo for )y reducing ates to the .rio made by sides with Hiragms are iguets by a number of small spiral springs, j)laced under a hard rubber ring wliich supports the diapliragm. The value of these last named improvements lies not so much in increasing tlie loudness of tone as in eliminating the reverber- atory quality characteristic of most of tlie early telephones, and which gave an unnatural and hollow sound to the voice trans- mitted by them. Foj. 12. Another of the forms designed by Mr. Plielps, and now being extensively introduced by the American Teloiihone Company, is repn;sentc"d in lig. 10. It consi.sts of a polislied oval shaped case of llard rubber, with magnet, diaphragm and coils inside. In con- nection witli this there is also a small magneto-electrical maclime, toutained in the oblong box shown iu fig. 11, which is used for 26 THE SPEAKING TELEPHONE. operating a call bell when the attention of the correspondent at the distant station is required. The currents generated by this machine, when the crank is turned, are convoyed by the conducting wires through the helices of a [)o]arized magnet, shown on the under side of tlie cover, fig. 12, and cause the ham- mer attached to the armature lever to vibrate against the bell, thus producing a violent ringing during the time the crank is turned. By the use of polarized magnets — the latter so named on account of their armatures being permanent magnets — the arma- ture levers are retained in a definite position, depending upon the direction of the current last sent into the line, and no retractile spring whatever is required. At the same time, also, the alter- nating currents produced by the magneto-electrical machine arc permitted to act with their maximum power, as the repelling force exercised in one pair of c )ils urges the armature in the same direction as that of the attractive force in the other, and the two effects are thus added. It is usual to supply two telephones with tliis apparatus — two being preferable to one — as then one can be held to the ear while the other ia being used to speak into. By this means any liability of losing a word while the instrument is l)cing passed from the month to the ear, supposing one <^nly to be used, is entirely prevented, and consequently the necessity for repetition avoided. When the telephone is not in use it is placed in a slide, as shown in fig. 11, which causes a spring, shown at the end of the box in fig. 12, to be pressed inward and cut out the instrument, leaving only the magneto machine and call bell in cu'ciit. The spring, when \a its normal position, on the other hand, cuts out tlie machine and call bell and leaves the telephone alone in circuit. Fig. 13 represents a somewhat more expensive but at the same time also a more desirable combination of the teleplione and its accessories. The box is intended to be fastened ]iermanently to the wall. It contains, in addition to the extra loud telephone PHKLl'S'8 DUPLEX TELKl'UONE. 27 3spondent crated by 3d by the I magnet, 3 the liam- t the bell, ! crunk is named on -the arma- upon the 3 retractile ', the alter- lachinc are 3 repelling turo in the other, aqd ratus — two e ear while means any iing passed be used, is ir repetition I a slide, as Q end of the instrument, rcuit. The nd, cuts out no alone in b at the same ieplione and permanently ad telephone with double diaphragms, which was described above, a call bell and a magneto-electric machine of improved construction. When not in use, only the call bell of this apparatus is in the main line circuit — the magneto machine, unlike that in the box just noticed, being cut out, so as to guard against accidental demagnetizaliou of FKg. 13. the permanent magnet by lightning discharges, or by currents from telegraph lines when the latter are crossed or in contact with the telephone line, which is sometimes liable to occur. When we wish to send a signal, however, it is only necessary to turn the 28 THE SPEAKING TELEPHONE. crank of tbo magneto machine, shown in front of the case, and at tbo same time press upon the push button C, which is visible on the left. The latter movement, by a change of connection to bo more fully described presently, puts the magneto machine in circuit, and thus allows the currents generated by it to pass into tlie line and act upon the distant call bells. The switch near the top of the case serves for cutting the ap- paratus in and out of circuit When it is turned to the right, and tho telephone is in the fork or holder, as represented in the figure — in which case it presses against a button correspond- ing to the spring in the former box and cuts itself out of circuit — only the call bell is left in with the main line. When it is Fig. 14. turned to the loft hand or opposite side, which should always be done whci left at night, all of the apparatus is cut out of circuit. A lightning arrester is provided in each box for the protection of the apparatus; but during thunder storms, and especially severe ones, it is best to cut the apparatus out of circuit altogether by means of the switch, as the best arresters sometimes fail. The accompanying diagrams, showing the internal arrangements of the different boxes, will give a much clearer understanding of the connections. Figure 14 represents the parts and connections of the improved apparatus, which is ])laced in a portable box, like the one shown in ligure 11, without, however, the addition MAGNETO- KLB:CTKIC JIKLI, CAM- 29 of what wo havo called tho extra loud Speaking 'relcphono. In tlio ordinary working condition of tho apparatus the switch S should bo 2>lac('d on tho button contact, sliown jimt to the rigiit of it, and the telephone hung in its fork, wliieh causes the spring A to be forced against the insido contact point. Tho telcplionc and magneto machine are thus cut out of circuit, as will be see > on tK.cing tho connections, but tho call currents arriving frc m a distant station on the line, find a ready path TS Fig. 15. through the coils of the bell magnet B and spring below the push button C to the spring A, and thence by switch S to line again or ground, as the case may be, the final connection de- pending, of course, upon whether the station is located some- where in the centre or at the terminal of the line. A call given liy any one of the stations in the circuits will, therefore, be heard at all tiie others, as the connections at each arc precisely similar. In giving the call, it is necessary, in addition to turning the crank of the magneto machine, to press against the push button 30 THK SPEAKING TELEPHONK. C, SO as to bring tlie adjacent spring in contact with the little connecting piece which is metallically joined to tlie coils of the machine. Unless this is done no current will be sent into the line, because it is by this means alone that the inductive appa- ratus is placed in the circuit. When the button is down, the path opened for tlie current may be traced from the line terminal of the instrument by way of the bell and magneto coils to the spring beneath C ; thence by way of spring A and switch S to line or ground. LIAIE UNE Fig. IG. It will be obvious that the above arrangement supplies the means for giving a variety of calls in case there are several offices in one circuit ; for, while turning the crank, the push button can be used, like a Morse key, to give different signals. The removal of the telephone from its fork or holder puts it in circuit, and cuts everything else out, as will readily be seen by tracing the connections. The manner in which the apparatus is cut out of circuit, by turning the switch S on the lefl hand con- tact point, will also be seen on referring to the diagram. Figures 15 and 16 show the internal connections and arrange- (IRAYS BATTKHV TKLEPUOXE. 31 meiit of tlio large box, figure 15, being the arrangement for a ter- minal, and figure 16 that for an intermediate station. The loud speaking instrument is shown in both. Figure 16 also shows the manner of connecting the condenser D around the bell coils, so as to avoid the previously noticed inductive difficulties which present themselves when many sets of the apj^aratus are placed in one circuit. The liglitning arrester is represented at L. It will hardly be necessary to say anytliing further in regard to the connections in the last two figures, as the same letters that were used in the preceding figure have been retained for correspond- ing parts in these, and have, therefore, been already considered. Fi'J. ' '. Figure 17 represents a form of Gray's Sneaking Telephone manufactured by the Western Electric Telegraph Company, of Chicago. Figure 18 shows a section of the same, reduced to about one third the natural size, and designed to show the internal mechan- ism. By referring to the latter it will be seen that the core C is fas- tened to the upper end of the curved metallic bar II, which serves as the handle of the telephone. The lower end of the handle is in like manner attached to the metallic brace B. To this brace is secured, by means of a stout screw, the iron rim 32 THE SPEAKING TELEPHONE. which holds the diaphragm ; thus the core and the diaphragm form the two ends of a rigid metallic system, every part of which is of sofl iron. Around the core two helices of insulated copper wire are wound. One of these — the polarizing helix — is somewhat longer than the other, and cotitains wire of larger gauge. In using the telephone, this helix is connected in circuit with a local battery. The soft iron system is in consequence rendered magnetic, the end of the core exhibiting opposite polarity to that of the dia- phragm confronting it. By employing the battery current to charge the soft iron core, Pig. 18. a greater degree of magnetism is thereby secured than could be obtained by the use of a permanent magnet of the same dimen- .ons. The difference also of magnetic potential existing between the diaphragm and tlie core is increased by making these respectively the opposite poles of the same magnet. The other hel'x is made of very fine wire, and serves to con- vey to the line the undulating currents induced by the vibrating diaphragm. At any point on the line these currents may be reconverted into sound by introducing an instrument similar to the above. GRAYS SPEAKING TELEPHONE. 88 In adjusting this telephone advantage is taken of the elasticity of the brace B, which hus a tendency to approach the handle II. This tendency is checked and regulated by the adjusting .screw A, a turn of which will cause the brace to move towards or recede from the handle ; and, consequently, the diaphragm will also move to or recede from tlie core of the magnet. • Another of the forms devised by Mr. Gray is shown in fig. 19. In I'li. t!i( 'ire two diuplirapms, and no battery is used to cliarLa iron cores of the telcplione, tis is done in the original ;qij)aratus, the same result being obtained by the use of a ]»ermanent magnet, bent into a form like the letter U, as seen iu the iigiu'c. The niagnet also answers as a handle, by which rves to con- Fig. 19. I tlie instrument maybe he. ! -on veniently. Two soft iron pieces I lire seeured l)y screws to the poles of the magnet and carry helii-es (it eopper wire, whieh are joined together, and terminal wires leading therefrom .serve to put the instrument in eireuit. The mouthpiece, wliich is of metal, lias two divergent tubes oon- iiivting with narrow chambers, within whieh .''(• pieces of the m.^gnet and in close proximity thereto. When- er. therefore, aiw -novement is produceil in the air at the Ji |.(iiiiiir of the till " 're resultant impulse is readily conveyed iiiiiifh it iind its l)i,ir.L'i)es to the ehamiiers. und thus eommuni- •'■s luutiuu to the diaphragms. The priuciple of the action in 34 THE SPEAKING TELEPHONE. this apparatus is, of course, the same as that in the other forms of ni'iguetc) telephones. It will be observed that all the Speaking Telephones which we have described, possess certain common characteristics em- bodied in Mr. Grav's o; 'wi^] discovery, and are essentially the same in principle althougi ing somewhat in matters of de- tail. All, for example, enij. . a diaphragm at the transmitting end capable of responding to the acoustic vibrations of the air ; all em])loy a diaphragm at the receiving end capable of being thrown into vibrations by the action of the magnetizing helix, correspondmg to the vibrations of the transmitting diaphragm ; all depend for their action upon undulating electric currents pro- duced by tlie vibratory motion of a transmitting diaphragm, which increases and decreases the number and amplitude of the electric impulses transmitted over the wire without breaking the circuit; and, fuially, in all practically operative tele])hones. whether A'ocal or harmonic, the cores of the receiving instru- ment are maintained in a permanently magnetic state by the inductive action, cither of a permanent voltaic current or of a ])ermanent magnet. Repeated experiments have shown, also, that this pcnnanent magnetic condition of the cores is absolutely essential, in order that the receiving magnet may become prop- erly responsive to telephonic vibrations, es])ccially when these are of great rapidity and comparatively small am))litude. Mr. Thomas A. Edison, of Menlo Park, New Jersey, has in- vented a telephone, which, like that of Gray, shown in figure 6, is based upon the principle of varying the strength of a bat- tery current in unison with the rise and fall of the vocal utter- ance. The problem of practically varying the resistance con- trolled by the diaphragm, so as to accomplish this result, was by no means an easy one. By constant experimenting, however, Mr. Edison at length made the discovery that, when properly prepared, carbon possessed the remarkable property of changing its resistance with pressure, and that the ratios of these changes j moreover corresponded exactly with the pressure. Fig. 20 rep- resents a couveuicut and ready way of showing the decrease in j KD13UX3 SPEAKING TELEPHONE. 86 i-t'si>tancc of tliis substance when so sul)jeete(l. The dcviec^ con- sists (jf ii carhon disk, two or three cells of liattery, and a tan- 'jcnl or other form of galvanometer. The carl)on C is ]ilaced be- 1 ween two metallic plates whicli arc jcnned witli the galvanome- tiT and hatterv in one circuit, through which the battery current is made to pass. AVheu a given weight is ])laced U])on the u])per ]il;ite the carbon is subjected to a definit(> amount of pressure, which is shown by the deflection of tlie galvanometer needle tlinmgh a certain nundier of degrees. As additional weiglit is added, the deflection increases more and more, .so that by care- fnllv noting tlie deflections corresjionding to the grafbial in- crease of pressure we can thus follow the various changes of resistance at our leisure. Here, then, was tlic solution ; for, Fi(j. 'JO. by vibrating a diaphragm with varying degrees of pressure against a disk of carbon, which is made to form a portion of an electric circuit, the resistance of the disk would vary iu ])reci.se accordance with the degreaof pressure, and consequently a proportionate variicion would be occasioned in the strength of the current. The latter would thas possess all the character- istics of the vocal waves, and by its reaction through the medium of an electro-magnet, might then transfer them to another disk, causing the latter to vibrate, and thus reproduce audible speech. Fig. 21 shows the telephone as constructed 1)y Mr. Edi- son. The carbon disk is represented by the black portion, E, near the diaphragm, A A, placed between two platinum plates, I ' and G, which arc connected in the battery circuit, as shown by till' lines. A small piece of rubber tubing, B, is attached to the ('••ntreof the metallic diaphragm, and presses lightly against an ivory piece, C, which is placed directly over one of the platinum 36 THE SPEAKING TELEPUONE. plates. Whenever, therefore, any motion is given to the dia- phragm, it is immediately followed by a corresponding pressure upon the carbon and by a change of resistance in the latter, as described above. The object in using the rubber ju.^t mentioned is to dampen the movement of the di.^k, so as to l)ringit to rest almost immediately after the cau.se which juit it in motion has ceased to act ; interference with articulation, which the prolonged vibration of the metal tends to produce in consequence of its Fig. 21. elasticity, is thus prevented, and the sound comes out clear and distinct It is obvious that any electro-magnet, properly fitted with an iron diaphragm, will answer for a receiving instru- ment in connection with this apparatus. Fig. 22 shows a sending and receiving telephone and a box containing the battery. In the latest form of transmitter which Mr. Edison has intro- duced the vibrating diaphragm is done away witli altogether, it having been found that much better results are obtained when a EDISON'S SPEAKING TELEPHONE. 37 .ison lias intro- Iv altogether, it ,btained when a. rigid plate of metal is substituted in its place. With the old vibrating diaphnigni the articulation produced in the receiver is more or less muffled, owing to slight changes which the vibrating disk ocea.sioiis in tlie pre^ssure, and which probably results from tanly dampening of the vibrations after having been once started. In the new arrangement, however, the articulatioa is Fig. 22. SO clear and exceedingly well rendered that a whi.sper even may readily be transmitted and understood. The inllexible plate, of c'oni'se, merely serves, in consequence of its comparatively large area, to concentrate a considerable portion of the sonorous waves 11] lull tlie small carbon disk or button ; a much greater degree of pressure for any given elTort on the i)art of the speaker is thus 88 THE SPEAKIXG TELEPHONE. lironght to boar on the disk thuu could l>o ubtaiuod if only its small surface ulono were used. The best substance so far discovered for these disks is lamp- black, such as is produced by the burnnig of any of the lighter hydrocarbons. Mr. Edison has found, however, that plumbago, hy])eroxidc of lead, iodide of copper, powdered gas ret(jrt car- bon, Uack oxide of manganese, amor])hous phosphorus, ihiely di- vided metals, and inan\' sulphides may be u.sed ; indeed, tufts of fibre, coated with various metals by chemical means and pres.sed into buttons have also been eni[)loyed, but tliey are all less sensi- tive than the lampblack, and have consequently been abandoned for the latter substance. With the telephone, as with the ordinary telegi-aphic instru- ments, there is of course a limit beyond which the apparatus cannot be rendered practically serviceable, but in most cases this limit is sooner reached for the telephone than for other instruments that are employed for the transmission of telegraphic matter. One reason why this is so is ])robably due to the fact that the ciuTcnt pulsations generated by the vibrating diaplu-agm arc made to follow each other with so much greater rapidity than those that are sent into the line by the ordinary hand manipulation, that less time is allowed for charging and discharging the line, and the phenomenon of inductive retardation thus becomes soonest manifest in the former case. Another reason, however, and perhaps the principal one, is that the disturbances created by the inductive action of elec- trical currents in neighboring wires combine with the signals, and so confuse the latter in many cases, that it becomes altogether impossible to distinguish them. It is necessary, tlierefore, when we wish to speak over long di.stance.«. or over wires in close prox- imity to Morse lines, either to employ some nicans for neutral- izing these disturbances, or to so increase the loudness of the ar- ticulation that it can be heard above this confused mingling of many sounds. One of the best means so far suggested for overcoming the diffi- culty is the employment of metallic circuits throughout for the EDISOXS TELEPIIOXTC REPEATER. 39 trlqilinnc, placiiif? the two wires forming a single circuit very (•los(! together, so as to render tlio iuductivo netion ])racticaily tlie same in eacli. Tlie resulting currents would thus neutralize each other and leave the telephone rpiite free. It is claimed that the inductiv^c disturbances just noticed are much less marked witli Mr. Edison's tele])hone than with any of the other forms, owing to the fact that the signals or sounds in the former are produced by stronger currents, and the re- eeiving iTistrumcnts arc made less sensitive to those fugitive currents that are always met with in telegraph lines. !^^r. Edison has recently invented a telephonic repeater, which is designed to bo used in connection Vi'ith his a})2)aratus for in- creasing the distance over which it may be made available. The principal ]iarts are shown in fig. 23. I is an inductioQ coil, whose M ^t-. i Fi'j. 2.3. pocondary is connected in the main line L', into which the repeat- ing is to be done; C is a carbon transmitter, included with hattery B in the primary circuit, and op(>rated by the magnet M instead of by the voice. The variations in the current pro- duced by speaking against the disk of the instrument at the transmitting end of the line, cause this magnet to act on the re- lieater diaphragm, and thus jiroduce different degrees of pressure im the carbon disk and thereby change its resistance. A coitg- sponding cliange consef|uently takes ]»lae(! in the current of the lirimary coil, and thus gives rise to a series of induce. 1 currents in the secondary, which i)ass into the line, and, on reaching 40 THE SPEAKING TELEPHONE. the receiver at the opposite terminal, are there transformed into uu(li1)le sound. Wc have not yet personally experimented with this apparatus, but if it can be made only in a .'flight degree as elfectivo as the ordinary carljon telephones, which already have 2:)ermitted conver- sation to be carried on over five hundred miles of actual tele- grai)h line, its advantage must sooner or later l)c made ser- viceable. ' Instead of tlie magneto machine and call bell, which have already been described in connection with the telephone, a bat- tery and vibrating bell may be, and sometimes arc used for sig- naling purposes. Fig. 24 represents the connections for an arrangement of this kind. The line wire is joined to the back end of a four point button switch, S. The right hand front con- tact leads to one end of the helices which surround the bell magnet, and whose opposite end is in metallic connection with the armature lever. In its normal ])ositi(in this lever is held by a spiral spring against the back stop, which is joined to a wire leading to the ground. The middle front point ot the switch communicates with one pole of a battery. E. whose opposite ])oie TELEPIIOXK AXn VIBBATINTr HEI,I,. 41 is ill connection with tlio ground wire, and tlio left hand point is coiiiu'ctc'd to one or two telephones, T, iilso in coinmunieation willi tli(! ground. Wlicii the iipparatus is not being used the switch is hh on llic riglit hand contact, so that a cun-cnt coming from tiie line liiis a frt'o })atli through the lieliccs, armature lever and hack stop to cartli. Tlie soft iron core is thus rendered magnetic and attracts tlie anuaturc, Init after the latter has moved ii short distance it leaves the sjmng forming \nirt of the back stop, and in so doing lireaka the circuit The magnetism of the cores coiiscMpieiitly disajijiears, and the armature is drawn back so as to complete the circuit once more, when another attraction fol- lows, and so the jirocess goes on alternating as long as battery is ispoiident when wanted ; the local battery has been oiuitted in the diagram. "When the switch is turned to the left the telephones alone are in circuit. 42 TlIK Sl'KAKINO TELEI'irONK. Ik'foro Ic'iviiit^' \\n' snlijcH't we iimst iikhv partionlarlv mention ()' e imiiit ill cnniu'ctiiiii therewith that, is of ton niueh interest to lie ()vei'h)()keil. Tiiis is in ivhitioii to the various charaeteristicM or forms of action that taive j)hiei! in the transmission of articu- late speech, and which furnish ns, in the o|)eration of tlio Spoiiking 'J'cle|)lioiie, with a most beautiful illustration of the correlation of forces, or of their mutual convcrtibilit}' from one form into another. When wc speak into a tclcpliono the muscular elforts exerted npon the luugs force the air through the larynx, within which are situated two mcm])ranc3 called the vocal chords. Tiiose can be tightened or relaxed at will by the use of certain muscles, and, being thrown into vibra- tion by the passage of the air, give rise to a series of sonorous waves or aerial pulsations, varying in pitch witli the tension or laxity of the chords. The impact of there pulsations against the metallic diaphragm produces, in turn, corresponding vibrations of the latter, wliich, as we have seen, is in close proximity to the poles of a permanent magnet. By tliis means, therefore, the inductive action of the diaphragm on tlie magnet is called into play, and there is consequently generated in the surrounding helix a series of electrical currents, which the intervening con- CORUELATIO.V oi' KOUCE3. 43 ductor conveys to tlio distant station, wliero their further action is then spent in the j)roductioii of magnetism. Tho receiving diaphragm, being then thrown into vihralion by tlic resalting attractions, rcsjioiid.s with faithful accuracy to tho vibrations origiudly produced at tho transmitting end of the line, and thus Pi-J. 20. also reproduces those sonorous waves which reach the ear and give us the sensation of sound. Here, then, we have, first, the mechanical cfFects of muscular action converted into electricity, then into magnetism, and finally back again into mechanical action. At each transformation, however, a portion of the u THK Sl'EAKlxa TELEPHONE. energy is lost, so far us its available usefulness is concerned ; and, therefore, the sound waves which reach the car, althougli pre- cisely similar in pitch and quality to those first produced by the vocal organs, are nevertheless much enfeebled — their amplitude, on which alone loudness depends, being diminished by the amount of energy lost in the transformation. rOj. 27. During tlie past year the articulating or Speaking Telephone has attracted very general interest and attention, not only in this country but also in Euroj)e. It has already been extensi\-fly introduced here upon inany of cur .'itch. of its own, and by whispering certixin vowels in succession a musical scale can be distinctly perceived. Our aim was to determine the natural pitch of each vowel ; but unexpected difficulties nuuh; their appearance, for many of the vowels seemed to possess a double 2>iteh— one due, probably, to the resonance of the air in the }nouth, and the other to the resonance of the air contained in the cavity behind the tongue, comprehending the j)harynx and larynx. lIKLMlIOi;i'/, S KXl'f^RlMKNTS. 51 I liit upoii an expedient for determining the jiitch, which, at tliat time, 1 thought to he original with inyself. It eonsisted in \ibrating a tuning fork in front of the mouth while the positions of the vocal organs for tlie various vowel sounds were silently taken. It was found that each vowel position caused the rein- forcement of some particular fork or forks. I wrote an at-count of these researches to Mr. Alex. J, Ellii?, ( >f London, whom I liave very great i)leasnre in seeing here to- night In reply, he informed me that the experiments related had already been performed hy Ilelmholtz, and in n much more perfect manner than I had done. Indeed, he said that Helm- holtz had not only analyzed the vowel sounds into their con- stituent nmsical elements, but had actually jjerformed the syn- thesis of them. lie had succeeded in jjroducing, artillcially, certain of the A-owel sounds by causing timing forks of diJQEerent pitch to vi- brato simultaneously by means of an electrio current Mr. Ellis was kind enough to grant me an intervi(.'w for the jjui-pose of explaining the apparatus employed by Ilelmholtz in 2)roducing these extraordinary effects, and I spent the greater part of a de- lightful (lay with him in investigating the subject At that time, however, I was too slightly acquainted with the laws of electricity fully to understand the explanations given ; but the interview had the effect of arousing my interest in the subjects of sound and electricity, and I did not rest until I had obtained ])Osscssiou of a copy of Ilelmholtz's great work,^ and had at- temi^ted, in a crude and imperfect manner it is true, to reproduce his results. While reflecting upon the possibilities of the pro- duction of sound by electrical means, it struck mo that the prin- ciple of vibrating a tuning fork by the intermittent attraction of an electro-magnet might be apjolicd to tlio electrical production of music I imaginc(l to myself a series of tuning forks of dilferent pitches, arranged to vibrate automatically in the manner shown 1 Ilelmholtz. Die Lohro von dom Tonompflndungon. (Unglisli translation, hy Aleiundor J. Ellis, Theory of Tone.) 52 THK SPEAKING TELEPHONE. by Helmholtz — eacli fork interrupting, at every vibration, a vol- taic current — and the thought occurred, Why should not the depression of a key like that of a piano direct the inteiTupted current from any one of these forks, through a telegraph wire, to a series of electro-magnets operating the strings of a piano or other musical instrument, in which case a person might plfiy the tuning fork ])iano in one place and the music be audible from the electro-niagnetic piano in a distant city ? The more I reflected upon this arrangement the more feasible did it seem to me ; indeed, I saw no reason why the depression of a number of ke3-s at the tuning fork' end of the circuit should not be followed by the audible production of a full chord from the piano in the distant city, each tuning fork affecting at the re- ceiving end that string of the piano with which it was in unison. At this time the interest wliich T felt in electricity led me to study the various systems of telegraphy in use in this country and in America. I was much struck with the simplicity of the Morse alphabet, and with the fact that it could be read by sound. Instead of having the dots and dashes recorded upon papei*, the operators were in the habit of observing the duration of the click of the instruments, and in this way were enabled to distinguish by ear the various signals. It struck me that in a similar manner the duration of a musi- cal note might be made to represent the dot or dash of the tele- graph code, so that a person might operate one of the ke3'3 of the tuning fork piano referred to above, and the duration of the sound proceeding from the corresponding string of the distant piano be observed by an operator stationed there. It seemed to me that in this way a number of distinct telegraph messages might be sent simultaneously from the tuning fork piano to the other end of the circuit by operators, each manipulating a differ- ent key of the instrument These messages would be read by operators stationed at tlic distant piano, each receiving operator listening for signals of a certain definite pitch, and ignoring all others. In this way could be accomplished the simultaneous transmission of a numl>cr of telegraphic messages along a single tel pe( pii anr TELErilOXIO CURREXTS. 68 a vol- )t the •upted rirc, to ano or lay tlie e from [casible )ression , should rd from t the re- . tiuison. 1 me to country ;y of the )y sound, aper, the the cUck stinguish (f a niusi- the tele- e key3 of iou o£ the ae distant seemed to messages UK) to the ig a difier- )e read by ■g operator snoring all nultaneous og a single wire, the number being Hmited only by tlio debcacy of the listener's ear. The idea of increasing the carrying power of a telegraph wire in this way took complete possession of my mind, and it was this practical end that I had in view when I com- menced my researches in electric telephony. In the progress of science it i.s universally found that com- plexity leads to simplicit}', and in narrating the history t)f scien- tific I'csearch it is often advisable to begin at the end. In glancing back over my own researches, I find it necessary to designate, by distinct names, a variety of electrical cuiTents by means of which sounds can be ])rodueed, and I shall direct your attention to several distinct species of what may be tei'med tele- phonic cuiTcnts of electricity. In order that the peculiarities of these cun'ents may be clearly understood, I shall ask Mr. Frost Direct Jntamittenti h, ft 3 yy i^^^Hi^k* d, A Fig. 29. to pmject upon the screen a graphical illustration of the different varieties. The graphical method of rej>resenting electrical currents shown in fig. 29 is the best means I have been able to devise of studying, in an accurate manner, the effects pniduccd by various forms of telephonic apparatus, and it has led me to the conception of that peculiar sjiecies of telephonic current, here designated as nndula- tory, which has rendered feasible the artilicial production of articulate speech by electrical means. A horizontal line {ij g') is taken as the zero of cnrrcnt, and im- pulses of positive electricity are I'cpresented above the zero line, and negative impulses below it, or vice versa. The vertical thickness of any electrical impulse {b or d), mea- sured fi'oin the zero line, indicates the intensity of the electrical 54 TIIK SPEAKING TELEI'HONK. current at llio point observed, and tlio liorizontal extension o{ the electrio line (b ov d) indicates tlie duration of the impulse. Nine varieties of telejilionic currents may 1)0 distinfruished, but it will only be necessary to show you six of these. The three primary varieties designated as intermittent, pulsatory and nndulatory, are re]U'eseuted in lines 1, 2 and 3. Sub-varieties of these can be distinguisluul as direct nr rc- vei-sed currents, according as the electrical impidses arc all of one kind or are alteraately positive and negative. Direct cur- rents may still further be distinguishiMl as positive or negative, according as the impulses arc of one kind or of the other. An intermittent (Hirrent is characterized by the alternate pres- ence and absence of electricity uj)on the circuit ; A i)ulsatory current results from sudden or instantaneous changes in the intensity of a continuous current; and An undulatory cuiTcnt is a cuiTcnt of electricity, the intensity of which varies in a manner proportional to the velocity of the motion of a particle of air during the production of a sound : thus the curve rejircscnting grai^hically the undulatory cuiTent for a simple musical tone is the curve expressive of a simple pendulous vibration — that is, a sinusoidal curve. I f lutermittont o o 2$ ~ E Pulsatory Undulatory Direct Direct Direct i Positive 1 Positive interniittent current. ( Negative 2 Negative " " Reversed S Reversed " " j Positive i I Negative 5 Reversed G i Positive I Negative 8 Negative Reversed 9 Reversed Positive pulsatory current. Negative " " Reversed " " Positive undulatory current. And here I may remark, that, althotTgh the conception of the undulatory current of electricity is entirely ciigmal with myself, methods of i)rodueing sound by means of intermittent and pul- satory cuiTents have long been known. For instance, it was long since discovered that an electro-magnet gives forth a de- VAdKH GALVAN'IC MI'SIC. 65 cklcd sound when it is suddenly mafrnctized or demagnetized. Wlien the circuit upon wliich it is ])]ac('(l is rapidly made and broken, a saecession of explosive noises proceeds from tlie mag- net. These sounds produce upon the car the cflEect of a musical note when the current is interru2)ted a safTuncnt number of times per second. The discovery of Galvanic Music by Page,! in 1837, led inquirers in difTerent })ai'ts of the world almost simultaneously to enter into the field of telephonic research ; and the acoiisti(!al effects produced by magnetization were carefully studied by Marrian,^ Beatson,^ Gassiot,* Do la Rive,'' Matteucci,' Guillemin,'' Wertheim,* AVartniann,* Jan- Jiiur,!* Joule, ^^ Laborde,!'^ Legat,is Reis,** Poggeudoi-fl, * * 1 C. 0. Ihge. " Tlie rroiUtctioii oC (ialvimio Miisio."' Sillimun's .Iniiiii., I'iST, xxxii. ji. a'.MJ ; Sillimuii'n Journ., isay, xxxiii. [>. lis ; Bibl. Uuiv. (uuw tiurius;, IsJJ'J, ii. i<. 3'J8. 2 J. P. ilarrian. Pliil. Mii(,'., xxv. p. 3«'J ; Just., IsiS, p. 20 ; Aroli. tlo I'Klectr., V. p. J!»5. 3 IF'. Heatson. Ak'Ii. ilu 1' Klccar., v. p. IHT ; Arcli. do So. I'hys. ct Nut. (L'd serifs), ii. p. 113. ^ Ocueiot. Sec "TreatiBo on Kleetrlcity," by Do In Rive, i. p. 300. " JJe la Rice. "TreiitiMU on Eleotricity," i. p. 300; Pliil. Mug., xxxv. p. 422; Aroli. Jc I'Kloctr. v. p. 'jm ; Inst. ]s4il, p. 83 ; f'oniptes Retx'.ds, xx. [i. l-.i-'T ; Comp. Koiid. xxii. p. 432; I'o^ ; Pogg. Ann. Ix.wii. p. 43; IJcrl. Bcr. iv. p. 121. " Elie Wartr/Kinii. Comp. Kond. xxii. p. 544; Phil. Miis. (3d series), xxviii. p. 544 ; Aroh. d. Sc. Phys. et Nut. (2d jiea), i. p. 41!i ; Inst. l8lii, p. 2ii0 ; Monutsolier. d.Berl. Akad. lS4i',, p. 111. 10 Jannair. Comp. Rend, xxiii. p. 319; Inst. 184ii, p. 2ii9 ; Arch. d. So. Phys. et Nut. (2d series), ii. p. 394. » 1 J. J'. Joule. Pliil. Mug. .xxv. pp. Ii',, 225 ; Berl. Ber. iii. p. 489. 1 8 Lahorde. Comp. Rend. I. p. 092 : Cosmos, xvii. p. 514. IS Legal. Brix. Z. S. ix. p. 125 1* lieis. "Telephonic." Polytechnic Journ. olxviil, p. 185; BiUtger's Notizhl. 1803, No. 0. IS ■/. C. Ihggendorff. Pogg. .Vnn. xcviii. p. 198 ; Berliner .Monutsber, 1S50, p. 133; Cosmos, ix. p. 49; Bcr!. Bcr. xii. p. 241 ; Pogg. Ann. Ixxsvii. p. 139. 66 TIIK Sl'KAKlXG TELEl'lIONE. Du Monocl,! Delozoniic' and otliers. ' It should also be men- tioned tliut Gore* ohtiiineil loud musical notes from mcreury, ucoiinpanied l)y sinjfularly beautiful erispations of tlie sur- face, during the course of exixiriments in electrolysis; Page* produced musical tones from Trevelyans bars by the action of the galvanic eiu'rent ; and furtlicr it was roduction of an instrument for making and breaking a voltaic circuit with extreme raiii. 402; Polytofiliiiic .Tourn. c.v. p. in ; Cos p. 4:1 ; Gli'isciier 'I'raiti! gem'Tul, iV-c. p. :i.")ii ; Dcivc-KpimtI. vi. p. ^)^ ; Vov .\Ui\. p. 411 ; liurl. Hui-. i. p. 144; Arch. d. So. I'ljys. ct Nat. xvi. p. 40il ; Encj'olopicdia dur Pliysik, pp. 1014-1021. * ifore. ProL'eodings of Koyal Society, xii. p. 217. S C. G. ruge. " Vibration nf Trovclyau'.-* linrs by tlic fralvaiiic current. man's .Tournal, ISoO, i.\. pp. 10.")-los. « Sullivan, "Currents of Eli^ctncity produced liy Ibo vibration ol' .Mctid.- Mag. Is45, p. 2(il; Arch, du I'jiluctr. .\. p. 4-0. ino.s, IV. ir. Ann. Kuiin'd " Silli- .'•riiii.
  • on tho circuit, so that a telegraphic despatcli sent by tho man- ipulation of tho key K' at the station shown in fig. 31, will bo received upon tho receiving instruments li' at ail tho other stations ui)on tho circuit. Without going into details, I shall merely say that the great defects of this j'lan of multiple telc- gra])hy were found to consist, firsth", in the fact that the receiving operators were required to possess a good musical car in orderto discriminate tho signals ; and secondly, that tho signal? cimld only pass in one direction along tho line (so that two wires wouhl be Jieeesdary in order to complete couiumuicatiou in both direc- 68 THE Sl'EAKXNO TKLKPUUNE. 1 1 i ! \ \ • \ • \ _'71»' '\ r \—^ r — 1 '■ 1 ■ - — 1 t- - '-: f- '-C : 1 f^r' 1 ._ . ■■'^ tl-^ . k> ; i t^ . ' M-l 1 -Jc ■ — -fed f* Er, * ^^ 1 1 i 'I- 1 i ■£. ", BS^M^IH 1^ iHr? ^ ■ II ^^^ 1 - - — i' - — ■S> w VIBRATORY CIRCUIT BREAKER 59 tions). The first objection was got over by employing the de- vice which I tenn a "vibratory circuit breaker," shown in the next diagram, whereby musical signals can be automatically re- coi'ded. Fig. 84 siiov/s a receiving instrument, li, with a vibratory cir- cuit breaker V attached. Tlio light s])ring lever V overlaps the free end of the steel reed A, and noi-mally closes a local circuit, in which may be placed a ^forsc sounder or other telegraphic apparatus. When the reed A is thrown into vibration by the passage of a musical signal, the spring arm V is thrown upwards, opening the local circuit at the point C. When the spring arm V is so arranged as to have uornially a much slower rate of vibra- tiou than the reed A, the local circuit is found to remain penna- Fig. u. . nently open during the viliration of A, tho spring arm Y coming into contact with the point only upon the cessation of the re- ceiver's vibration. Thus tiie signals ])rod\iced by the vibration of the reed A are reproduced u])on an ordinary telegraphic instru- ment iu the local circuit. Fig. .35 shows tlie a})])lication of electric telcpl ony to auto- graphic telegraphy, q. '/ represent the reeds of transiuiti';.^ nistru- ments of dilTcrcnt pitch, s, s the receivers at the distant statuMi of correspcniding pitch, and u, u, etc'., the vibratory circuit breaki rs attached to tlie receiving instrument's, and connected with meta.lic bristles resting upon chemically prepared jiapcr iv. The mes.sagc or picture to be copied is written upon a metallic surface, p, with non-metallic ink, and placed upon a meUUlic cylinder connected with the main l)atterv, c; and the chemically ])repared paper, upon which the message is to l)e received, is j^laccd u]:)ou a 60 THE SPEAKING TELEPHONE. metallic cylinder connected with the local battery d at the receiving station. When the cylindera at cither end of the cir- cuit are rotated — but not necessarily at the same rate of speed — a fac simile of whatever is written or drawn upon the metallic surface^ appears upon the chemically prepared ])apcr w. The method by means of which musical signids may be sent simultaneously in both directions along the same circuit is shown in our next illustration, figs. 36, 37 and 38. The arrangement is similar to that shown in figures 81, 32 and 33, excepting that the interinitteut cuiTciit from the .transmitting iustrumeuts is passed /•7f/. :i5. through the ]inmarv wires of an indiietitm coil, and the receiving instruineuts are placed in circuit with tlie sco )ndarv wire. In this way fi'eo cartli communication is secured at either end of the circuit, and the musical signals produced by the manii)ulation of any key are received at all tlic stations upon tin? line. The great objection to tiiis plan is the extreme complication of the parts and the necessity of employing local and main batteries at every station. It was also found by practical ex])erinient that it was difficult, if not iinpos.sible, upon either of tlio jdans hero shown, to transmit simultaneously th<5 number (jf musical tones MULTIPLE TELEGRAPHY. 61 62 THE SPEAKIXG TELEPHONE. that theory showed to 1)e feusible. Miiture consideration re- vealed the fact tiiat this diiliculty hij in the natnro of the electrical current cmjiloyed, and was finally obviated by the invention of the undulatory current. It is a strange fact thiit impoi'tant inventions are often made alrno.st simultaneously by diilerent persons in dillerent parts of the world, and the idea of multiple telegraphy, as developed in the preceding diagrams, seems to have occurred independently to no less than four other inventoi-s in America and Europe. Even the details of the arrangements upon circuit — shown in figs. 31, 32, 33 and 36, 37, 38 — are ex'.emoly similar in the plans proposed by Mr. Cromwell Varley, of London, Mr, Eiisha Gray, Mg. 39. of Chicago, Mr. Paul La Cour, of Copenhagen, and 'Mr. Tliomas Edison, of Newark, New Jei-sey. Into the question of priority of invention, of course, it is not my intention to go to-night That the difficulty in the use of an intermittent current may be more clearly understood, 1 shall ask you to accompany me in my explanation of the elfect produced when two musical signals of different pitch arc sinmltaneously directed along the same circuit. Fig. 39 shows an arrangement whcrel)y the reeds r r' of two transmitting instrument'^ are caused to interrupt tlic current from the same battery, B. We shall suppose the musical interval between the two reeds to be a major third, in which ca;c their vibrations arc in the ratio of 4 to 5, i c, 4 vibrations of r are made in the same time as 5 vibrations of r'. A and B represent the intermittent currents produced, 4 ini- MUi;iIl'I,K 'IKLKGliAl'llV. pulses of B being mado in llic samo tiiuo ii.s o impulses of A. Tho line A -|- B represents tiu; resultant effect upon tlu; main line wlieu tho reedi^ r and r' arc; simultaneously caused to make and break tho same circuit, and from the illustration you will perceive that the resultant current, whilst i-etaining a \iniform intensity, is less interrupted when both reeds are in ojjeration than when one alone is employed. By carrying your thoughts still further, you will understand that Avhen a large number of reeds of diHerent pitch or of ditl'erent rates of vibration arc sim- ultimeously making and breaking tho same circuit, thi'. resuitant effect upon the main line is practically ei[uivalent to rgaiis, and I liaV/. 47. brano. I determined, tlicrefore, to construct a phonautograpli modelled still more clo.sely upon the rneclianism of the human ear, and for tliis pnrpo.so I sought the assistance of a distin- guished anri.^t in Boston, Dr. Clarence .1. Blake. lie suggested the u.se of the liumaii car itself as a ]>hoiiautograpli, in.rana tympani and the ossiculas with a mixture of glycerine and water the necessary mobility of the parts was obtained, and upon singing into the external artificial car the .stylus of hay was thrown into vibration, and tracings were obtained upon a piano surface of smoked glass jiassed rapidly underneath. While engaged in these (>\- pcriments I was struck with the remarkable disproportion in weight between the membrane atid the bones that were vibrated by it It occurred to me that if a membrane as thin as tiss\ie paper could control the vibration of hones that were, compared to it, of immense size and weight, why should not a larger and thicker membrane be able to vibrate a piece of iron in front of an electro-magnet, in which case the complication of steel rods show^n in my first form of telephone, fig. 45, covild bo done away with, and a simple piece of inm attached to a membrane be placed at cither end of the telegraphic circuit. Fig. 48 shows the form of apparatus that I was theit employ- ing for producing undulatory currents of electricity for the pur- j)oses of multiple telegra])liy. A steel reed. A, was clamjjcd firmly by one extremity to the uncovered leg h of an electro- magnet E, and the free end of the reed projected above th(> covered leg. When the reed A was vibrated in any mechanical way the battery current was thrown into waves, and electrical undulations travci-sed the circuit B K W E', throwing into vibra- tion the corresponding reed A' at the other end of the circuit. I immediately proceeded to i)ut my new idea to the test of practical experiment, and for this purpose I attached the reed bell's INOPEKATIVE TE1RT.H0NK. 71 A (fig. 49) loosely by one extremity to the uncovered polo h of tlio mag!ict, uiid fastened the other extremity to the centre of a stretched membrane of goldbeaters' akin n. I ]iresuinc(l that upon speaking in the neighi)orhood of the membrane nit would be thrown into vibration and cause the steel reed A to move in a similar manner, occasioning undulations in the electrical cur- rent that would corres])ond to the changes in the density of the air during the production of the sound ; and I further thought that the change of the intensity of the current at the receiving end would cause the magnet there to attract the reed A' in such a manner that it should copy the motion of the reed A, in which case its movements woiUd occasion a sound from the mendirane n' similar in timbre to that which had occasioned the original vibration. Fig. 49. The results, however, were unsatisfactory and discouraging. My friend, Mr. Thomas A. Watson, who assisted me in this iirst experiment, declared that lie heard a faint sound proceed from the telephone at his end of the circuit, but I was unable to verify his assertion. After many experiments, attended by the same only partially successful result.'^, I determined to reduce the size and weight of the spring as much as possible. For this purpose I glued apiece of clock spring, about the size and shape of my thumb nail, firmly to the centre of the diaphragm, and had a similar instrument at the other end (fig. 50) ; we wen; then enabled to obtain distinctlv audible effects.' I remember ' On tho 14th of February, ISiTj, Mr. Klisliii Crniy, of Chictt(,'o, filed ii cuvoat in the Patent OfHcu at Washington, Joscribing tlie Spualviiig Telephone shown in flgiirc Ii, page 15, and which, npon examination, will \n: found to be identical witli lluit shown in fiirures f.O and U'l. On the Haiiic day Professor Rell filed an applica- tion in the Patent Ollicu at Washington, Ueseribing the apparatus shown in liguro 72 THK SPEAKING '1 KLEPlloNi:. an cxn. rimjiit in;i(le with this telephone, which ;it tlio time gave me givat .viiiskctioii ami delight Quo of tlic telephones was I'htced in ii'y lecture room in tiio Boston University, and the other in the basement of the adjoininle])hon(! to oljserve the; elTects of articulute speech, 'vhile 1 uttered the sentence, 'Do yuu Firj. 50. understand what I say?' into the tele]>hone placed in the lecture hall. To my delight an answer was returned through the in- struinc-' *■ itself, articulate sounds ])roceeded fn^m the steel spring attach('(l to the membrane, and I heard the sente-iee, "Yes, I understand you ])erfeetly " It is a mistake, however, to suppose /"(■;/ . Tii. that the articulation was l)y any means jierfect, and expectanev no douL* had a great deal to do with my recognition of the sentence; still, the articulation M-as there, and I recognized tiic fact that the indistinctness was entirely due, to the imperfection of the instrument. I will not trouble you by detailing the 49, wliicli lie horci aekiiowlodges would not work, mid it was not until after ho ha.i substituted tlie apparatus shown in Mr. Grav'^" ••avcat in iilare of it. tliat hr wis enulih'd to suceessfull.v acconiplisli the (rrand ohjuot of reproducing urticulate Hpeceh at a distuuue. See note, i)a^'e Tv.— G. 13. I'. fJKAYS TELKPIIONIC TKAXSMrrj'ER. 73 various stages tlirough wliicli ihe jipparatu;-; missed, Imt shall merely say that after a time I j)n)duee(l the form of instrument tiliDWii in fig. 61, wliieii served wry \yo\\ as a receiving lele- plione. ]ii this ecndition my invention was exhibited at the Centennial Kxhihition m Philadelphia, The telephone shown in fig. 50 was iisecl as a transQiittiiig instrument, and that in fig. 51 as a. reeeiver, so that vocal couimuiueatiou was only established ni oiu! direction. An(jther fonn of Iransmitting teie])hone exhil)itcd m Phila- ndin(? of the tc.\t it iniplit bo erroneniisly int'iiri>il thiit the iippiirntu."* hIiowm in iijfuri; 52 was invented by I'rot'es.sor Boll, and exhibited by hmi ut tho i'eiiteiinial Exhibition. Priilehsor Bell neither invented nor exhibited it. Tho iilxive fiirure rein'eseiitu tlio tri'iisiiiittinLf porti'in of Eli.-ilia Gray'n oriirinal Speakiiii; Telei>hcini' - the tirst articiilatintr ti'lephono ever invented. Tlie eonipli te apparatus iH sliown in tiirnro <1, jiane 1.''. Mr. (iniy exporinieiited with his telepliono at the Oentennial Exhiiiition at IMiilu(lel|)hia in l^Vci.^ons to investigate tlie I subject, ann' distinctly audible to an audience of six hunaratns required, and I aiu ha])py to reconl the fact that they (•(Uninnnicated to me each now discovery as it was made, and eveiy new step in their investigations. It was, of course, almo.sti* inevitable that these gentlemen should retrace much of the ground \ that had been gone over by me, and so it has happened that I many of their discoveries had b<'(>n anticipated by my own re- searches ; still, the very hoiinraliKj way in which they, from time to time, placed before mo tlie I'osults of their discoveries, entitles them to my warmest thanks ami to my highest esteem. It was always my belief that a certain I'atio would be found Ix'tween the several parts of a telephdne. and that the size of the instru- rnont was inunaterial ; but Professor Poircc was the first to de- mcmstrati! t\\o extreme smalluess oi the magnets which might 1)(> em])loyed. And lu're, in order to show the parallel lines ni which W(! wer(^ working, I ma\' mention the fact that two or thi'ee days after I had constructed a tele|ihone of the jiortable form (lig. 55), containing the magnet inside the handle, Dr. Chainiing was kind (Miougli to send me a pair of telephones of a siniil.ir pait^'rn, which had been invented by the Pro\-i(li^nce experimenters. The eonveuunt form of mouthpiece shown m c tl I'EIUCES TELEl'IIONK MOUTHI'lliCl-;. 77 i\'j. 55, now iulopted by lac, was iuveiitod .solely by iny friend, Pvofessor Peirfo. I must also express my oblii'-atioiis to my frii'iiil and associate, Mr. Tlioimis A. Watson, of .Salem, Massa- ehusetts, who has for two years past given ine his pereonal assist- ance in carrying on my researches. In pursuing my investigations I have ever had one end in view — the practical improvement of electric telegraphy — but I have eotae across many facts which, while having no direct bear- ing upon the subject of telegra])hy, may yet pcjssess an interest for you. * / For instance, I have found that a musical tone ])roceeds from a piece of ])lumbag(j or retort carbon when an intermittent cur- rent of electricity is passeil through it, and I have observed the ^ most curiiKis audible elfcH'ts produced by the passage of reversed | intermittent currents through the human body. A rheotome was placed in circuit with the ])rimary wires of an induction coil, and the line wires were connected with two strips of brass. One of these strips was held closely against the ear, and a loud sound [)roceeded fi'om it whcncvei' the other slip was touelied with the other liand. Tiie stri])s of brass were ne.xt held one in eacli hand. " The induced (nirrents occasioned a muscular tremor in the iingci's. Upon placing my fordinger to my ear a loud crackling noise was amlible, seemingly proceeding from the lin- ger itself. A friend who was }jresent ])laced my linger to his ear, but heard nothing. I requested him to hold the strips him- .self. lie was the listinctly cor icious of a noise (which I was unable to perceive) proceeding from his linger. In this case a portion of the induced currents jjassed through the head of the observer ■< "n he ]/K.ced his ear against his own linger, and it is possib' rhat the sound was occasioned by a vibration of the surfaci's ..f the ear and linger in contact. When two per.=i-ns receive a shock from a RuhmkorlT's coil by clasjjing hands, ^.ach taking hold of one wire of the coil with the free hand, a st)und proceeds from tlie cliisped lumda 'i'lie ^, 1 f^co liesearcheg in Telephony. Trons. of .\inerionti Aoud. of Arts iinJ Scioiioos, vol. xii. ]). 1, 78 THE SPKAKING TELEPHONE. effect is not produced when the hands uro moist. Wlion either of the two touclics the body of the otlier u li^nd sound comes from the parts in contact Wlien the arm of one is ])laced against the ai'ui of the otlicr, tlie noise proiluced can be heard at a distance of several feet In all these cases a sliglit shock is experienced so long as the contact is preserved. The intro(hiction of a piece of paper between the parts in contact does not materially interfere with the pnjduction of the sounds, but the unj)leasant effects of the shock are avoided. / When an intermittent current from a liuhndcorff's coil is ) passed through the arms a musical note can be perceived i^ I when the ear is closely applied to the arm (^f the person experi- \ mcntcd upon. The .sound seems to proceed from the muscles of the fore-arm and from the biceps muscle. IMr. Elisha Grayi has 5 Fig. ftS. also produced audil^h* clTt-etx bv the pa-sage of electricity through the hunijiu bod v. An extremely loud nuisical r>>te is occasioned })y the spark of a Ruhmkorff's coil when the primary circuit is made and broken with sufficient rapidity. When two rheotomes of different pitch are caused simultuieously to open and close the primary circuit a double tone proceeds from the spark. A curious discovery, which may be of interest to yon, has been made by Professor Blake. lie constructed a telephone in which a rod of soft iron, about six feet in length, was used instead on impiiry this proved not to have jeen the case. Attention having thus bceti directed to the phenomenon, a watch was kept \ipon tlu> instruments, and 6U THK SPEAKING TELEPHONE. npnn a sniisoqnont occnsion tlio samo fact was ohsorvod at both cuds of the lino \>y Dr. Cluimiing ami liis friends. It was prov^od that tlio sounds oontinuod for al)oiit two hours, and usually com- menced about tlie same time. A .searching examination of tin; hue disclosed nothing abnormal in its condition, and I am unable to give you any explanation of this curious phenomenon. Dr. Chauning has, however, addressed a letter u])()n the subject to the editor of one of the Providence pajjcr-s, giving the names of such .songs as were recognized, with full details of the obser- vations, in the hope that ])ublicity may lead to the discovery of the performer, and thus aflord a .solution of the rnj'stery. My friend Mi; Fredcric^k A. Gower communicated to me a curious obst'i'vation made by him regarding the slight earth con- nection required to establish a circuit for the telephone, fmd together we carried on a series of experiments with rather start- ling results. We tooic a coujDle of telephones and an insulated wire aliout 100 yards in length into a garden, and were enabled to carry on conversation with the greatest ease when we held in our hands what should liave been the earth wire, so that the con- nection with the ground was formed at cither end through our bodies, our feet being clothed with cotton socks and leather boots. Tlie day was fine, and. the grass uj)on which we stood was .seemingly perfectly dry. Upon standing upon a gravel walk the vocal sounds, though much diminished, were still per- fectly intelligible, and the same result occurred when standing upon a bri<;k wall one foot in height, but no sound was audible when one ot us stood upcin a block of freestone. One experiment which we made is so very interesting that I must speak of it in detail. Mr. Gower made earth connection at his end of the line by .standing upon a gra.ss plot, whilst at the other end of the liiKs I stood upon a wooden board. [ re- quested Mr. Gower to sing a continu(;us musical note, and to my surpri.se the .sound was very distinctl> audible from the telc- [thone in my hand. LIpon examining my feet I discovered tha.t a single blade of grass was bent over the edge of the board, and that my foot touched it. The removal of this blade of grass PHKECKH TKLKl'IloNIC OHSKUSATIONS. 81 was followed liy tin; cossatiou of tli(! sound from the tcleplionc, and 1 found that tlu! moment I touelied with the toe of my l)oot a l)la(lc of f^niss or tlie petal of a daisy the smnid was ag'ain aiulible. The quostion will naturally arise. Throu^di what lenuth of wire can the telephone he used? In reply to this [ may say that the maximum amount of resistance; tln'ouLdi which the un- dulatory current will ]iass, mid yet, retain sudieient force to pro- duce an auilil)le souny Mr. Preece : " Wiiilc on the one part Professor Bell has placc(I in our hands, to a certain extent, a new power, lie has, on the <)th(>r hand, thrown upon our shoulders an extra weight. The poor telegraph engineer has now to master many .sciences. Not only must he know something of electricity and magnetism — notonly must he know a good deal of chemi.stry — not ordy must lie |)ass through various stiiges of mathematical knowledge, hut now, thanks to Professor Bell, he is ohliged to he master of the in- tricacies of acoustics. I do not blame him, because the study of .«o)md is in itself a beautiful occupation, and when it becoines linked to one's profession it becomes almo.st a luxury. Professor Bell alluded to the ^act that ex])cctancy led him in his first teleplume to anticipate what was said. I will give you an illu.stration of the effect of expectancy. It was my pleasure, on a recent occasion, to exhibit the telephone before a very large audience. Many learned men were present There is one very remarkable feature of a learned meeting. When you call u])on a learned member to make a learned remark he frequently malces a foolish one. Now, I selected one of the leading scien- tific men of the day, and placed the telephone in his hand. It was in connection with a similar instrument fifty-five miles away. Of couree we expected to hAI). 1 Of all modern iiivontioiis coiinccteil with the transmission of telegnipliic! signals, the tek-phoiii', devised l)y Mr. Alexander r interval. The essential ])art of the instrument consists of an electro-magnet with an iron armature attacheil to one end of a lever. At the otluM' end of the lever is a pointer or pencil, and a paper ribbon moves at a constant rate in front of the end of the pointer. When the coils ol the elcctro-niagnct arc traversed by a current, the iron armatui'c is attracted, and the pointer comes in contact with the paper ribbon, on which it makes a mark, long or short, according to the duration of the cui ront Thus are produced the dots and dashes. These arc combined in a similar way to the right and left movements of the needle in the needle iustruracut In some UNDri.ATIXr. CI'IUIKXTS. 85 H :i of tlio more reiinccl instruments letters arc indicated and even printed directly at the receiving station. Tlii.s is. of course, a great simplilication ; but with such arrangcniciits we cannot liuve more tliaii tliis. The page of print rei)resents the limit of wiiat such instrimicnts and methods can do for us. It is true that a skilled operator with the Morse instrument can interpret the sig- nals as they arrive without looking at the murks on the paper, simply by using his ears. i<]vcry time the circuit is made or broken a click is heard, and long practice has taught him to i-ely on the evidence of his ears with as much confidence as one less accustomed to the work would trust his eyes. Nevertheless, he hears only a succession f)f clicks, which must Ijc interpreted before th(y becom(» intelligible to any one but himself. In these forms of apparatus, it will be observed, the eiirrents are intermittent; each current, circulating through the coil, is followed by an interval of rest. Tluy begin and eml ;ibru!itly, and all perform the same kind of work; that i.s, they (h'llect a needle, or produce mai'ks on a jiiecc of paper. Telc})honic cur- rc'its. on the other hand, rise and fall, ebb and ilow. chang(> in intensity within comparatively wide limits, but pi'cserve their continuity so long as "(Uitinuous sounds arc being uttered in the neighborhood of the telephone. Tiny ari' called nndulatory current.s, to distinguish them from the intermittent currents of tlic ordinary telegraphic apparatus ; and their peculiar character is an essential feature of the telephone. No skill or training is required for the efl'ectivo use of the telephone. The operator has merely to press the instrumcit to his ear to hear distinctly every .sound transmitted from the dis- tant end. For this, it is true, an eflort of attention is rc(juired, and some persons use the insti'ument at the tirst trial with more .success than othcns. Individuals diifer in the facility with which they ure able to concentrate their attention on one car, so as to be practically insensible to what goes on around them. But this habit of attention is readily acquired, and when it is once accpiired tJie telephone may l)e used by any one who has (\ai's to hear and a tongue to spe;'' . In sending a message, the iustru- 86 TIIK .Sl'KAKlNci TKI-KIMIONE. ment is held aVtoiit i\n iiicli in front of the mouth, and the sender merely tiUlvs into the inoutlipiecc in his ordinary, natural man- ner. The words are repeated by tlie instrument at the other end of the circuit with the same pitch, the same cadences, and the same relative loudness. But what strikes otio the most is that the character of the speaker's voice is faithfully preserved and reproduced. Thus one voice is readily distinguished from another. No peculiarity of inflection is lost Nor is this result effected over short distjuices only. No doubt a sen- tence will be heard with diminishing distinctness as it comes over an increasing distance. In this country cxjieriments have not yet been made, so far as we know, over very long dis- tances; but Mr. Bell states that he carried on a conversation without any difficulty between Bo.'ston and Now York, two hun- dred and fifty-eight miles apart, through an ordinary telegraph wire. A man's breathing was distinctly heard one hundred and fortv-nine miles away. At the Newport torpedo station, in Rliode Island, speaking was carried on through a line including five miles of submerged cable and an equal length of land wire. Resistance coils were added two thousand ohms at a time, until twelve thousand ohms were introduced into the circuit, without interfering with the transmission of speech. Tlie importance of this test will be understood when it is remembered that the ve- sistimce of the Atlantic cable is e(pial to seven thousand ohms only. 1 The experiments at Newport were continued by the addi- tion of a total resistance of thirty thousand ohms, but beyond twelve thou.sand ohms, tlie sound was found to diminish in inten- sity. Mr. Bell states that the maximum amount of resistance through which the undulating current will pass, and yet retain sufficient force to produce an audible sound at the distant end. 1 It by no meiinH follows, as the writer would lend us to infer, that the tclopUono ciui be used tn triiiisinit artiouliite s|iui'oh throii^fh i:xti'iide;ni;ths of eahlo simply beoauso it has s.rved well, under very dissimilar eireiimstuiices, to eomiriunieate throu);h un etiuivalent resistaneo of artifleiul line. The hnvs retrardinj^ tlie phenom- enon of induetive retardation in lonjf oeean eables. like those aeross tlie Atlantic, liold (food for eurrerts produeed by the teleiihone as well as for currents derived from any other source whatever. IXDfCTlOX (TRRKNTS. 87 has yet to be determined. In the laboratory he has conversed through a rosistanco of sixty thousand ohms. Tliere is a prac- tical diiliculty in traiismitting telephonic signals through a tele- graph wire running parallel to a number of other wires which are being used for ordinary telegraphic purposes. Induction currents are produced in the telephone wire, whi(fh greatly inter- fere with the distinctness of the sounds. The difliculty is said to be overcome by having an e.xtra return wire, instead of util- izing the earth for a part of the (tircuit, as is ordinarily done. The two wires are put side by side in close proximity, ami the detrimental cllcct of tlie inductive currents is thus partially or entirely disposed of. The following extract from a letter which appeared in the Daily News a few weeks ago shows that induc- tive action, when the parallel circuits are not numerous, does not seriously interfere with the transmlssi(jn of speech: The experiments with the telephone were made by mo upon the cable lying between Dover and Calais, which is twenty-one and three-ipiarter miles long. Several gentlemen and ladies were present, and conversed in French and English with a second party in France for upwards of two hours. There was not the slightest failure during the whole tune. I was only using one wire. The other three (it is a four wire cable) were working di- rect with London and I'aris, Calais and Lille. I could distinctly hear the signals by the three wires on the telephone, and at times, when but one of the three wires was working, 1 could decipher the Morse signals, and read a message that was passing from Glasgow to Pans. Yet when all the tliree wires were working simultaneously, the telephone sounds were easily and clearly distinguishable above the click of the signals . I hap- pened to know several of the ])arty in France, and was able to recognize their voiee.>*. They also recognized mine, and told us immediately a lady spoke that it was a female voice. When making some trials upon a line three fourths of a mile long, I arranged a musical box (the tones of wliich are very feeble) un- der the receiver of an air-pump, the top of the receiver being open. Upon this opening I placed the telephone, and every 88 THE SPEAKTXrr TELEPHONE. note came out at tlio second en J so clearly as to enable those who were present to name the tune that was played. Unfortunately we liad not the same means in Knvnce, but simply iield the jnouth of the telephone close to tlie box, and some of the notes were audible, but not so perfect as on the short line. One younf^ lady burst out laughing tlie moment she placed the instrument to her ear, and exclaime!, ''Si /me one is whistling, 'Tommy, make way for your uncle!'" As my correspcmdont and my.self liad had a little practice, we were, without the slighte.st difliculty, able to talk in our usual manner, without any strain upon the voice or any uimatural lengthening of .syllables. We were not able to hear bre.-ithlng, in conseipicnce of the continued ])ecking caused bv indnetion from otiier wires. The construction of the telephone (tig. 57) is remarkably simple. Fig. 57. It consists of a steel cylindrical magnet, about five inches long and three eighths of an inch in diameter, encircled at one ex- tremity by a short bobbin of wood or ebonite, on whicii is wtjund a quantity of very fine insulated copper wire. Tlie magnet and coil are cont;iined in a wooden cylindrical ca.sc. The two ends of the coil are soldered to thicker ])ieces of copper wire, which traverse the wooden env(^lo]ie from one end to the other, and terminate in the binding sei'cws at its extremity. Inunediately in front of the magnet is ;i thin circular u'on plate, wiiich is kept in its place by being jiunmed between the main portion of the wooden ease, and a wooden cap carrying the mouth or ear trumpet. Tlieso two jiarts are screwed together. The latter is cut away at the centre, so as to expose a portion of the iron plate, TlllCKNKSii UK 'I'llK DIAI'IIHAOM. 89 iib)Ut half iin iiicli in diameter. In the experiments which Mr. Bell lias carried out in order to determine the influence of the vari- ous piirts of the teleplionc on flic results j^rodnced, and their rela- tions to each othorwhen the best elfeets ar(!ol)tained, he ciiijiloyed iron jihites of various areas and tiiicknesses, from hoiler plate tliree-eighths f an inch in tliiekncss to the thiimest ]ilate pro- <'urable. Wonderful to relate, it ajipears that scarcely any plate is too thin or too thick for the purpose, hut the hest thickness is that of the ferrotype plate used by jihotograjihers. Thin tin plate also answers very well. The iron plate is cut into the form of a disk, ahont two inches in iliauieter, and is placed as near as possilile to the extremity of the steel magnet witiiout actually toucliing it; the cfleet of this position lu'ing that, while the in- duced nuignctism of the plate is considerahlc, it is .susceptible to very r,\\ui\ eliMUges. owing to tlus freciloin with which the plate can vibrate. The dimensions of the various parts oC the instru- ment her(! given are found to lu; convenient, but they are by no uiciiiis essential. Good results have been obtaiiuMl by means of a magnet only an inch iind a half long, and a working instru- ment need not be to(j large foi" the waistcoat jjocket. There is no dillerencc between the transmitting and the receiving tele|ilione; each instrument serves both ])urposes. Nevertheless, in order to avoid the ineonvenience of shifting tin; instrument backwards ;••.({ forwards bet'- en the ear and iIk^ n.'outli. it is better to have two on the circuit at each .station. The operator then holds one |icnnanently to his ear, while he talks with the other. it will not be suppos(>d that tlic^ idea of this marvellously .simjile piece ot .-qjparatus w;is cvolveil ready formed from the inventors brain: veiy far otherwise. It is the final outcome of a long series ot ]);itient researches c;irried out by ^[r. Bell in the most SKI ful and nnUoson hieal manner, in which one modilica tion suirifested another, accessorv a fter accessorv was Hiscardci and linallv the instrument was i)runed d and dunensions. Teh iMHiones b own to its ]ircs(Mit form iv(^ i)een lonji Known. Af ew rebv articulate sounds could years ago a simple arrangement wher l)e transmitted over a distance of liftv or sixtv vards, oi' e\en fur- 90 rilK SI'KAKINU TKLKPUONK tlicr, could !)(• l)i>ii!i-lit ill tin- .streets for ii penny. It consisted of ii piiii' ol" pill l)o.\es, tiie bottoms of wlii(!li were connected by a piece of string stretclied tight, wliihi over tlus mouth of each was ))astod tissnt^ ])aper. On speaking to mw of tiie jiill boxes the tissue ])aper and I'Ueloseil air were set in vibration. 'Die vibra- tions so ])roduccd were eonnnunicated to tlie thread and tnms- mittcd to the distant ])ill box, wliieli wa- held cK)se to tlie ear, where they affected the air in such a way as to reproduce the original sounds. Tlie sim])le apj)aratus was more effective than would be at first imagined. Electric telephones were devised in this country about the same time that the telegraph was intro- duced, but the best of them d'ffered widely from the modern in- strument. They were (•apal)le of eoiiveving to a di.stance sounds of various pitch, so that the succession of notes constituting a melody could be reproduced many miles away, but the special character of thi' voice by which the melody was oi'iginated was entirely lost. ^ Now tli(> great interest which attaches to Mr. Bell's telephone, and the intense wonder and curiosity it has aroused, are due to its ])OW(>r of conveying aV).solutely unaltered every peculiarity of voice or musical instrument, A violin note rea{>])ears as ii violin note : it cannot be mistaken for anything else. And in the case of a human voice, it is not less easy to distinguish one speakei- from another than it would bo if the speakers were in the room close liy instcail of being miles or even hundreds of miles away. 'IMiis is the charm of the new telephone; this it, is which renders it immeasurably superior to anything of the kind which prt'ceded it. Mr. Bell's researches in el(!Ctrio telephony began with the arti licia! proiluetion of musical sounds, suggested by the work in which he was then engaged in Boston, viz: teaching the deaf and duml) to speak. Deaf mutes are dumb merely because they are deaf. There is no local defect to prevent utterance, and Mr. Bell has jjractically demon.strated by two tlum.sand of ' Rc'ihs'k teli-'plione was tlio first inveiitioti which could lu'oompli.sli tlio ri'siilt here Htated. ami this was mvcnti'il in (funimiiy, in tHiil. Scu (Ifsuripticm of Kuiss's tclephoui', \>ui!v II. TKACINGS OK AlK VIUllATIONS, 91 his own pujiils Unit wli 'ii tlio deut' and dumb know liow to con- trol tlio iictioii ()[ tlioir vocid organs, they van urticiiihito witli conipiinitivo fticility. Striving to perfect his system of teaching, it oeetirred to Mr. Bell that if, instead of presenting to tiie eye of tiie deaf mute u system of symbols, lie couhl make visible the vibrations of the air, the apparatus might l)o used as a means of teaching articulation. In tliis ]iart of his investigations Mr. Bell derived great assistance from the phouaulograpli. He suc- ceeded in vibrating by the voice a style of wood, about a foot in length, attached to tiie mend)rane of the phonautograph ; and with tills he obtained enlarged tracings of the vibrations of the air, ])roduced by tlie vowel sounds, upon a i)lane surface of smoked glass. Mr. Bell traced a similarity between the manner in which this piece of wood was vibrated by the membrane of the iihonautograph and the manner in which the ossiculte of the human ear were moved by the tympanic membrane. Wishing to construct an apparatus closely reseml)ling tlie liuman ear, it was suggested to him by Dr. Clarence J. Blake, a distinguished aurist of Boston, that the human ear itself would l)e still better, and a specimen was prcjiared. Our readers are aware that the tympanic membrane of the oar is con- nected with the internal ear by a series (jf little bones called res pectively the malleus, the incus and the stapes, front their [)ecu- liarsiiapes. and that by their means the vibrations of the tympanic membrane are communicated to the internal ear and the audi- tory nerves. Mr. Bell removed the stapes and attached to the end of the incus a style of hay about an inch in length. L'pon singing into the external artilicial ear, the style of hay was thi'owii into vibration, and tracings were obtained upon a ])lane surface of smokeil glass passed rapidly underneath. The curves so ob- tiiined are of great interest, each showing peculiarities of its own dependent upon the vowel sound that is sung. Whilst engaged in these experiments Mr. Bell's attention was arrested by obi-erv- ing the wonderful dispi-oportion which exists between the size and weight of the membrane — no thicker than tissue paper — and the weight of the bones vibrated by it, and he was led to 92 TIIK UPKAKING TKUKl'HONE. inquire wlictlicr a tliiuker iiu^ml)riui(' iniglit not he iiblf to vibrali- ii piece of iron in front of an clectro-iMagiu't. TIk^ exjieriiuent was at once tried. A piece of steel spring was attached to a stretched membrane of gold beater's skin and })laeed in front of the pole of th»^ magnet Tiiis answered very well, but it was found that the action of the instrument was improvi'(l by in creasing the area of nietid, and thus the menil)rane was done away with and an iron ])lat(> substitute(l for it. It was important at the same time to determine tlmelTeet produced by altering the strength of the magnet; that is, of the current which ]iassed round the coils. The battery was graduall}' rcibiccd from lifty cells to none at all. and '<. however, ultimately reached. Iieyoud whicli no improvement was efTected, aniatiou liy strikinj^ or drawing a violoncello how ai'i'oss its ])roujrs. The fork yields its own proper jiotu, which will be loud or the reverse, accordinte vibrates cxactlv twice as fast as the other. If tho one performs a hundred oscillations in ji second, the other which is an octavo above, comj)letes two hundred in the same interval of time. Thus, tho pitch of a note yielded by a tuning fork Te isii tiiird, cqimlly, if not iiioro iin- jMirtniit, iiiifl t)y no mciiiis so simplf of cxpliiiuitioii. W'c rcfr-r to what is usually spoken of in Knirlisli books on acoustics as the (juality of the note ; the Freiieh ciill <' tinil)re and the (Jor- inaiis klan^ffarbe. It is that which constitates the dillcrcnce be- tween a violin and an or^Mii, or between an or^un and a |iiiino- forte, or between two human voi 'cs ; ind(.'cd between any two musical sounds which are of the same pitch and louchiess, but are still distiuffuishable from each other In order to explain the physical cause of quality, we will suiiposc we have ;i thin metallic wire about a yard lon when vibratinj^ in this manner is called its fuiulanu'iital note. If the wire be damped a^ its centre, by layinj^ on it witii slight pressure the; feather of .i quill pen, and pluck«'d at a [loint half way betwcvn the cientre and one end, both halves will vibrate in the same manner, and independently of each other. That is to say, there will 1)G two eipial vibrating segments and a point of rest or node nt the centre. ]?ut the rapidity of vibration of each segment will be twi(!e as great as tliat of th(! wire -rhen vibrating as a whole, and consequently the note emitted will be the octivve of the fun- damental. When damped at a point one third of the length from either extremity, and ])Iucked half way between that point and till* nearer extremity, the wire will vibrate in three ccpial di\ i- sion.s, just as it vibrates in two divisions in the previous oas^e. The rate of vibration will be now three times as great as at fii-st, and the note produced will be a twelfth abov(! the funda, mental. Similarly, by damping and plucking atsuitidile ])oints the wire may be made to vibrate in four jkuLs, live; part.s, six parts, etc., the rate of vibration increasing to four, five, six, etc., times what it was at fii-st. Let us suppose that when the wire was swinging as a whole, and sounding its fundamental 96 'rriK SI'KAKINC TKI.KI'HOXE. iiot(\ the number of oscillations po I'l'ormed in a second was one liundivd. Then we sec that by takinji' suitable j)i'eeautions tlie wire can Ijcniade to break up into two, three, I'our, live, six, etc., vibrating segments, the rates of vibration l)eingres[)ectively two hundred, three hundred, four hundred, live liunibvd, six liundred, etc., and the series of note.s emitted being the octave abcjve the fundamental, the lifth above the octave, the double octave, the third and fifth above the double octave, and so on. We now come to an important point, which is this — that, the wire l)eing free, it is practically imiiossible to .strike or pluck it in such a way as to make it vibrate aecoi'ding to one of the above systems only. Jt will vibrate as a whole wherever and however it be struck, but this mode has always a.ssociated with it or superpo.«ed upon it .some of the other modes of vibration to which we have just re- feiTed. In other words, tlie fundamental note is never heard alone, but always in condonation with a certain nuird)er of its overtones, as they arc called. Each form of vibration called into exi.stenee sings, as it were, its own song, v.-ithout lieecling what iy being done by its fellows, and the con.sequencc is that the sound which reaches the ears is not simple but highly coni[)()sit'j in its character. The word clang has l)een siiggestcd to denote such a eomjKxsite sound, the constituent simple sounds, of which it is the aggregate, being called its 1ir.st, second, thii'd, etc., partial tones. All the po.^sible partial tones are not necessarily present m a clang, nor of those which are present are the intensities all the same. For instiinee, if the wire l)e struck at the (,'cntre, that point cannot be anode, but must be apointof maximum disturbance : hence all the even partial tones an; exchulcd and only the odd one.s, the first, third, fifth, and so on, are heard. That characttristic of a musical note or clang, which is called its quality, denends upon the number and relative intensities of the i)artial tones which go to form it. The tone of a tuning fork is approximately simple ; so is that of a stop[)cd wooden organ pipe of large aperture blown by only a slight pressure of wind. Suoh tones sound sweet and mild, but also tame and spiritles.s. lu the clang of the violin, on the other liand, a large number of SOUNDS OF THE IirMAN VOICK. 9/ partial tones arc represented ; lienec tlie vivacious and brilliant character of this instrunieiit. Tlic sounds ol the human voice arc ])roduced by the vibrations of the vocal chords, aided by the resonance of the mouth. Tiic si/.e and shape of the cavitv of the mouth may be altered by opening and closing the jaws, and bv tightening or loosening the lips. We should expect that these movements would not bo without elTcct on the resonance of the contained air, and sucli proves on experiment to bo the fact. Hence, when the vocal chords have oi-iginatcd a clang contiiining numerous well developed partial tones, the mouth cavity, \>y successively throwing itself into diflerent postures, can favor by its resonance first one overtone and then another ; at one moment this group of partial tones, at another that. In this manner endless varieties of quality are rendered possible. Any one may prove to himself, by making the experiment, that ■when singing on a given note he can only change from one vowel sound to anotiier by altering the shape and size of his moutli cavity. Having thus briefly indicated the physical causes of the vari- ous diircrences in musical notes, and the production of sounds by the organ of voice, we will devote a few moments to consider how these sounds arc propagated through the air and reach the plate of the telei)hone. When a disturbance is produced at any point in an aerial medium, the particles of which are initially at rest, sonorous undulations spread out from that point in all di- rectiona These undulations are th .Tect of the rapid vibratory motions of the air particles. The analogy of water waves will help us to undcrsUmd what is taking place tinder these circum- stances. If a stone be dropped into the still water of a pond, a series of concentric circular waves is produced, eacii wave con- sistinff of a crest and a hollow. The waves travel onwards and outwards from the centre of disturbance along the surface of the water, while the drops of water which constitute them have an oscillatory motion in a vertical direction. That is to say, fol lowing any radial line, the water particles vibrate in a direction at right angles to that in which the wave is propagated. The 98 THE SPEAKING TELEPHONE. distance between two successive crests or two si\ccessive hollows is called the length of the wave ; the amplitude of vibration is the vertical distjince through which an individual drop moves. In a similar manner sonorous undulations are propagated through air by the oscillatory motion of the air particles. But tiiere is this impoi'tant diilerence between the two cases, that, in the lat- ter, the vibrating particles move in the same direction in which the sound is being propagated. Consc(iuont]y such waves are not distinguished by alternate crests and hollows, but by alter- nate condensations and rarefactions of the air, the transmission of which constitutes the transmission of sound. The wave length is the distance between two consecutive condensations or rarefactions. It depends upon the pitch of the transmitted sound, being shorter as the sound is more acute, while the extent of vibration of the air particles increases with the loudness. Such are the peculiarities of the vibratory motion in air corresponding to the pitch and loudness of the transmitted sound. But what is there in the character of the motion to account for diilerence in quality? A little consideration will show that there is only one thing loft to account for these, and that is the form of the vibration. Let us incntally isolate a particle of air, and follow its movements as the sound passes. If the disturbance is a simple one, produced, say, by the vibration of a tuning fork, the motion of the air particle will be simple also, that is, it will vil)rate to and fro like the bob of a ])endulum, coming to rest at each end of its excursion, and from these points increasing in velocity until it passes its neutral point Such, however, is clearly not the only mode of vibration possible. If the disturb- ance bo produced i)y a clang conij)rising a number of j)artial tones of various intensities, all excited siniultiineously, it is ob- vious that the air particle must vibrate in obedience to every one of these. Its motion will be the resultant of all the motions due to the separate partial tones. We may imagine it, starting from its position of rest, to move forward, tlien stop short, and turn back for an instant, then on again until it reaches the end of its excursion. In returning it may perform the same series of to- tl s a St SONOROUS UNDULATI'^NS. 99 and-fro motions in the opposite direction, or it may move in a totally different way. Nevortholess, however complex its mo- tion may be — and, as a rule, it will be cx-jccdingly complex — its periodic character will be maintained. All the tremors and per- turbations in one wave length will recur in all the other?. When sonorous undulations impinge u])on the iror plate of the telephone, the latter is set in vibration. Its particles move to and fro in some way or other. The complexity of their mo- tion will depend upon that of the air from which it was derived But for the sake of simplicity we will assume that the plate has a simple pendulous motion. It will be remembered that the iron plate is placed (juite close to, liut not (piite in contact with, '.he extremity of the steel magnet It becomes, tlierefore, itsf If a magnet by induction ; and, as it vibrates, its magnetic powei is conhtantly changing, being strengthened when it approaches the magnetic core, enfeebled as it recedes. vVgain, when a magnet moves in the neighborhood of a coil of wire, the ends of which are connected together, an electrical current is develojied in the coil, whose strength depends ujion the rapidity with whicli, and the disUmce through which, the magnet moves. In the t(!lei)hone then, as the plate moves towards the coil, a current is induced in the latter which traverses the whole lengtli of wire coimecting it with the disUmt instrument ; the plate returning, another current with reversed sign follows the iirst The intensity of these cur- rents depends, a.s we have said, on the rapidity with which these movements are effected, but is largely influenced also by the fact that the plate does not retain a con.stant magnetic strength throughout its excursions. Under the a.'^sumption we have made with respect to the simplicity of the plate's motion, it follows that the induced currents, alternately positive and negative, fol- low each other in a uniform manner, and with a rapidity corre- si)onding to the pitch of the exciting note. These currents pass along the circuit, and circulate round the coil of the distant tele- phono. There they modify the magnetic relations between the steel magnetic core and the iron j)late in such a way that one current — say the positive — attracts the plate, while the other 100 THE Sl'EAKIXG TELEPHONE. — the negative — repels it And since the arriving currents fol- low each other, first positive and then negative, with perfect regularity, the plate will also vibrate in a uniform iiianiier, ;ind will ])orl'onn the same number of vil)nitions per second as did the plate of the sending instrument Hence the sound heard will be an exact copy, except as to loudness, of that produced at the sendmg stiition. Having thus followed the sequence of phenomena in tliis simple case, we are enabled to extend our explanation to the case in which composite sounds of more or less comjilexity — vowel sounds and speech — are transmitted. We are compelled to admit that every detail in the motion of an air particle, every turn and twist, nuist be passed on unaltered to the iron mend)rane, and that every modilication of tlie motion of the membrane must have its counterpart in a mochtication of the induced currents. These, in their turn, alfecting the iron plate of the receiving telcj)hone, it follows that the plates of the two telephones must be vibrating in an absolutely identical manner. We can thus follow in a general manner the coui-se of the phenomena, and explain how air vibrations are connected with the vibrations of a magnetic plate — how these latter give rise to electrical currents, which, passing over a circuit of hundreds of miles, cause another magnetic plate to vibrate, every tremor in the first being reproduced in fae-simile in the second, and thus excite sonorous undulations which juiss on to the ear. We can understand all this in a general way, but we are not the less lost in wonder that the sequence of events should be what it is. That a succession of currents could be transmitted along a tele- graph wire without the aid of a battery, that, by simply talking 1o a magnetic membrane in front of a coil of wire, the relations of the magnetic field between the two could be so far modified as to produce in the coil a succession of electrical currents of sufficient power to traverse a long circuit, and to reproduce a series of phenomena identical with those by which the currents were brought into existence, would ha,ve been a few yeara ago pronounced an impossibility. A man would have been derided who proposed an instrument constructed on such principles. UNiVE^lSITY OF VICTOftl>.> Victort*, 8 C. NIOLES TUBULAll El-ECTRO- MAGNET. 101 Nevertheless, here it is realized in our hands. We can no longer doubt, we can only wonder, and admire the sagacity and pa- tience with which Mr. Bell has worked out his problem to a suc- cessful issue. 1 The articulating telephone of Mr. Graham Bell, like those of Reiss and Gray, consists of two parts, a transmitting instrument Fig. 60. and a receiver, and one cannot but be struck at the extreme simplicity of both in.struments; so sin)]ile, indv .', that were it not for the high authority of Sir William Thomson, one might be pardoned at entertaining some (h)ubts of their capability of producing such marvellous results. The trausmittiug instrument, which is represented in fig. 60, Fiij 01 consists of a horizontal elcctro-maiiiiet, nttachcd to a pillar about 2 inches ai)ovo a hori/contal mahogany stand ; in front of the poles of this magnet — oi', more correctly speaking, magneto-electric inductor — islixed to the stand in a vertical j)lanc a circular brass ring, over which is stretched a mcml)rane, carrying at its centre a small oblong jiicce of soft iron, which plays in front of the in- ' iMiu'liiecriiii;, I"-". 102 THE SPEAKING TELEPUONE. 'Inctor mapfnet wlienever the membrane is in a state of viliration. 'I'liis membrane can be tightened like a drum l)y tli(! three mill lieaded screws shown in the drawing. The ends of the coil sur- rounding the magnet terminate in two binding-screws, by which the instrument is i)ut in circuit with the receiving instrument, which is shown in fig. 61. This instrument is nothing more than one of the ttibular elcetro-magnets invented by M. Nicies in the year 1852, but which has been reinvented under various fancy names several times since. It consists of a vertical bar electro-magnet inclosed in a tube of soft iron, by which its mag- netic field is condensed and its attractive power within that area increased. Over this is fixed, attached by a screw at a point near its cii'cnmfercnce, a thin sheet irc.n armature, of the thick- ness of a sheet of cartridge pajjjr, and this, when under the influence oi the transmitted currents, acts partly as a vil)rator and partly as a resonator. The magnet with its armature is mounted upon a little bridge, which is attached to a mahogany stand similar to that of the transmitting instrument The action of the ai)paratus is as follows: When a note or a word is sounded into the mouthpiece of the transmitter, its mem- brane vibrates in unison with tiie sound,, and in doing so carries the soft iron indut-tor attached to it backwards and forwards in presence of the electro-magnet, inducing a series of magneto-elec- tric currents in its surrounding helix, which are transmitted by the conducting wire to the receiving instrument, and a con-e- sponding vibration is therefore set up in the thin iron armature sufficient to ])roiluce sonorous vibrations, by which articidated words can be distinctly and clearly recognized. In all previous attempts at producing this result the vibrations were produced by a make and break arrangement ; so that, while the number of vibrations per second, as well as the time measures, were correctly transmitted, there was no variation in the strength of the cur- rent, whereby the quality of tone was also recorded. This de- fect did not prevent the transmission of pure musical notes, nor even the discord ])roduced by a mixture of them, but the com- plicated variation of tone, of <|uality, and of modulation, which WORKIXG OVKU AUTIFICIAL LINK. 103 make lip tlie human voice, required 8onietliing more than a mere isochronism of vibratory impulses. In Mr. Bell's apparatus not (mly are th(! vilirations in the receiving instrument isochronous with those of the tran.smitting membrane, but they arc, at the same time, similar in ({ualit}'' to the sound producing them ; for, the currents being induced by an hiductor vibrating with the voice, differences of am[)litude of vibration c;inse differences in strength of the impulses, and the articulate sound as of a person speaking is produced at the other end. 1 Th(! telephone has been regarded as a toy, or a curiosity to be played with ; but, while it is undoubtedly extremely interesting as a novelty, it is very much more than ,iiis; it is, scientifically and practically, a great success. Tliere are, undoubtedly, diffi- culties in its use, but, considering that it is a contrivance but of yestenhiy, the wonder is that it is so perfect. When a telegraphist ".rst gets into his hand this beautifully simple and electrically delicate instrument, his first inclination is to test its carrying power. This is, of course, a closet experiment, not working with actuid telegraph line, but with a resistance coil equivalent to a telegraph line of stated length. An experiment of this nature gives Ijctter results than could be obtained by a veritable line, because the insulation is, so to speak, perfect. No leakage at undesigned points of contact, or disturliance from un- favorable atmos[)heric conditions, is felt, and the experiment is entirely under the observer's control. The apparatus used is designed to offer the .sime lal)or for the electric current to over- come as woidd be ollered by a stateil length of outside telegraph line, 'iliis artificial resistance is nicely graduated, and, as the method of testing was suggested by Ohm, a German electrician, the unit of resistance is termeil an ohm. Removing the tele- I)hone to such a distance that the two observers wen; out of ear- shot, the test with resistance was tried, and with a resistanc(! of 1,000 ohms — roughly speaking, e([ual to seventy miles of a well constructed line — the sound was perfect, although not very loud. I Climiihers' .liiinial. 104 THE SPEAKING TELKPHONE. Kvery .irtionlation of tlio speaker at the other end could he dis- tinguislicd s(j long as silence was maintained in the room, or so l(jng as no heavy lorry rumbling over the stones outside sent in no liarsli noise which drowned the faint w]iis})er of the instru- ment. The resistance was gradually raised to 4,000 ohms — nearly 800 miles — with like favorable results ; and for some lit- tle distance beyond, articulation could still be made out. But by the time 10,000 ohms had been applied, ])uttiiig the speaker at a distance of, say, 700 miles, sound only, but not articulate sound, reached the car. The tone was there, and every inflection of the voice could be followed, but articulaticn was absent, although the listener strained every nerve to catch the sound, while the s]ieaker, as was afterwards ascertained, was shouting in a loud, clear voice. The prolonged notes of an air sung could be heard with the resistance, but again no words could be distinguished. The next experiment was to join uj) the telephones in the olHce with diirei'cnt line wires in succession going to various distances, and working with different kinds of telegraph in.stru- ments. When this was done, the real obstacle to teleplionic progress at once asserted itself in the shape of induction. The first wire experimented with was 2)artly overhouso and partly underground, and the offices ujjou it were working Wheatstone's step-by-step dial instruments. It is difficult to render clear to the person ignorant of telegraphic ])henomcna the idea exi)ressed by the word induction. Brit'llv, it maybe }nit thus : that, when aa electric current is passing on a wire, it has the faculty of setting up a current of opposite character in any wire in its vicinity. In various recent articles on the telephone, mention has l)eon made of contact as the cause of disturbance. This wonl, how- ever, althougli it has been used by telegraphists, is misleading, and can only be used as an endeavor to express popularly an electric fact. Actual contact of one wire; with another would spoil the business altogether. A wire bearing an electric cur- rent seems to be for the time surrounded, to an undefined dis- tance, by an electric atmosphere, and all wires coming within DIFFICULTIES FROM INDUCTION. 105 this .atmospiiprc have a piirrent in an opposite direction set up in them. Tiiis i.s as near an exphination of the ])henornena of in- duction as thi! state of telograpli science ut present affords. Now, tlie telephone worlcs with a very delicate niad for private telegra]>hy, or for the least important i)ublic unices, because it re(iuires no code to be learned by the manipu- lator, .so it woidd likel) be the first to be displaced if an acoustic tt'legra])h jiermanently took the field. So the sentient little Wlieatstone dial opens it.s mitrailleuse fire on the intruder, on who.se delicate current.s, in the words of an accomplished elec- trician, it ])lay.4 old Harry. The peculiar character of the sounds we borrow on the tele])1ionc from this instrument ari.ses from the fact that, as the needle flies round the dial, a distinct current or ])ulsation i:)as3cs for each letter, and the final op we have tried to 10»3 THE SPEAKING TELEPHONE. roprcsoiit shows tlic stoppa;.'!* <)f the ncedlo at the letters as words woro spcllofl o\it. It iimst not 1)0 understood that the sounds of those various instrniiieuts are actually heard in the telephone. What happens is, that the currents .stealin;^ ulonj^ th(^ telephone wire liy induc- tion ])roduco vilirations in the diaphrajrni of that instrument, the little nu'tal ineud)rane workinjr on the niajruet in ready response to every current. set ui)l)y the latter. When it isrenieniliered that the i)riiiciple of the tele})houe is that the sounhonc wire, cause disturbances in the sound vibrations, and th<>reby cripple the instrument One instnnuent of either kind named would have a certain efTect, but one Morse would not have any greatly ])rojudicial effect. But a nuinlicr of Morses going together, such as were heard in our exi)eriments, would cond)inc to be nearly as bad as onc^ W^heatstonc dial or fast- speed Monse. So delicate is tlu^ diaphragm to sound (and neces- sarily so) that, in all experiments with the telephone itself, every sound from without broke in. giving eilect like the well-known niunuur of the shell. Joining up our wire now to a more ilistant station at .sonu^ miles along the railway, and having on its poles a nundier of wdiat are known as heavy circuits, the ])ot-iK)iling sound assumeil even more marked characteristics. The Wlu-aistone dial n<) longer alh'cted \is ; but a number of Morse instruments were in full gear, and tlui fast-speed transmitter was al-so at work. While we were listi>ning, the circuit tatstone dial was, however, absent, so that our experiment ])roved highly suc- cessful. For some rea.son or another — jirobably an imperfect condition of the wire, or the efTeets of induction over and above 108 TlIK SPEAKING TKLKI'HONE. what inado itself an(lil)lc to us — tlic si)oken sounds wore deficient in distinctness: but souffs sunjjf at either end were verv beauti- fully lieunl, and, indeed, the sustained note of sunjf words had always a better carrying ])o\ver than ra[)idly spoken words. Every syllable and every turn of melody of such u song as ■• My Mother liids me Bind my Hair," sung by a lady at oiu' end, or " When the Heart of a Man," sung at the other, could lie distinctly heard, but with the elleet before noticed, that the voice was mullled or shut in, as if the singer were in a cellar, while it was not always jiossible to say at once whether the voice was that of a man oi" a woman. In the course of some domestic experiments it was remarkcvl that, in playing the scale downward from C in alt on the piano, the result to the listener was a tit only for the four ujiper notes, although all bcjow that had a clear ting, and the octaves below were mostly distinct, although at the low notes of the ])iauo i!ic sound was again lost. The ringing notes of a m.isical box were not .'^o successful, but, with close attention, its rajiid execution of '• Tommy Dodil " could be well enough made out. An enrocoss n[ tiippiiifr liy t('l(']ilioiu> <'nMl(l not lie carricil (lilt if the iiistniiiu'iit in use was a WlioatstoiK! dial ssfully us(m1 where its wire is absolutely isolated from all other telect wiis the same as before. The ringing is heard both when 1 C. G. PuKC, Silliiuuu's Jcjurnul, vol. xxxii., p. 3iMi, July, 1S.'37. TONKS PRODUCED «V KLECTKICAli CIRKENTS. Ill the contuct is made imd In-oken ; when tlie contact is made, tiio sound emitted is very feeble ; wlion l)i'okoii, it may he heard at two or three feet distance. The exj)erimf'iit will hardly succeed with small magnets. The first used in tiic exjieriment consisted of three horseshoes, supporting ten pounds. The next one tried was compo.sed of six magnets, su])porting fifteen pounds by the armature. The third suppoi't(>d two jiound.s. In each of these trials the .sounds produced differed from each other, and were the notes or pitches jiecnliar t(j the several magnets. If a large magnet supported by the bend be struck with the knuckle, it gives a musical note ; if it be slightly tapped with the finger nail, it returns two sounds, one its pro])er musical pitch, and another an octave above this, which last is the note given in the ex})eri- ment ox THE DISTURBANCE OF MOLECULAR FORCP:.S BY MAGXETLSM. * A .short article on this subject appeared in the last number of this journal under the caption, '' Galvanic Music." The following experiment (as witnessed by yourself and others not long since; ailords a striking illustration of the curious fact, that a ringing .sound accompanies the disturbance of the magnetic forces of a steel bar, provided that bar is so poised or su.sjiended as to ex- hibit acoustic vibrations. An electro- magnetic bar four and a half inches in length, making five or six thousantl revolutions })er minute, near the poles of two horseshoe magnets properly suspended, produces such a rapid succession of disturljanecs that the sound becomes continuous and much more audible than in the former experiment, where only a single vibration was pro- duced at a time. TOXKS I'RODUCEI) HV ELECTRICAL CURRENT.S. 2 Mr. Page was the first to discover that an iron bar, at the moment it became magnetic through the galvanic current, gave a ])eculiar tone, and this fact has since been confirmed by Mr. Delezennc. 1 C. 0. Piitfi', SiHiniairs .loiinial, vol, xxxiii., p. Us, ()otiil)or, l^rit. » W. Werthuiiii. Auimleii dur I'liysio uiul Chomio. L.WVIt, .luiiu, ISiy. 112 THK SI'EAKINCr TELEPHONE. Without being awaro of tliis discovciy, I publislied, in 1844, a trcntiso in wliicli I dealt witli several (juestioiis relating to this subjeet. In this work I attempted to prove : 1st. That the elcetrieal eurrent eauses a temporai'v weakening of the eoeflieient of the elastieity of iron. 2d. That likewis(>. tlie magnetization is aeoompanied by a very slight deerease of the eoeflieient of the elastieity of the iron, which diminishes only ])artially when the magnetizing cnrrent is inter- rupted, and tliat this result does not manifest itself at onee, but only upon the continued action of the currents. The production of sound thnnigh the outside current (that is, {[ current wliieh ]ias.ses through a helix in whose axis is an iron bar or extended iron wire) was lirst accurately noticeil by Mr. Marrian. According to these physici.sts, the sound |)roduceil was identical with that obtaineil by striking the rod on eillu'r ntes this movement to a temiiorarv increase ol! the elasticity of tiie iron effected liy magnetization. vVt the same time I delivered to the academy a short note, in which, without entering into the details of the experiments, 1 explained the results wiiidi I had obtained, and how. according to my opinion, the .sounds were to he accounted for. The pres- ent treatise contains develoiiments and proofs to sustain the opinions given l>y me at that time. Jt seems superfluous to repeat here the discussion wliich occurreil at the time of writing this note, between Ak'ssrs. De laliive, (luillcmfn and Wartmann. I desire simply to say that the last named scientist was the lirst to notice that a current passing through a wire may ])roduce a sound without then; being, in the wire, a resistance of any amount to oppo.se. Sound may therefore be produced as well in an iron bar as in an extended iron wire, heat having only an insignili- cant ])art to jilay in the phenomenon. Later on Mr. De laEive senta treati.«c to the Royal Society, in London, which dealt with a jiart of this subject. After admit- ting that no .sound is producc(l ly ;i current pa.ssing through any metal, other than iron, he goes on to describe a new class of facts. All conductors, when expo.scd to the inlluence of a powerful electro-magnet, give, at the moment of the jia.s.sage of an inter- rupted electrical current, a very distinct sound, similar to that of Savart's cogged wheel. Tlie influence of magnetism on all con- ducting bodies .seems to c;onsi,st in its imparting to the latter, similar })roperties to tho.se possessed by iron in it.self : thus devel- oping in these conductors tiie pro])erty of emitting sounds whicii are shnilar to those given l)y iron and other metals without aid from the action of a magnet. VIURaTIONS of TKEVELVAN'.S BAHS 1!V 'I'IIK (lALVANIC crUUKXT. * The vibrations of Trevelyan's bars l)y the action of heat i.s an experiment more interesting than familiar, and one whicli » Silliimm's Journal, 1850. Vol. ix., p. lO."). 114 THE .Sl'EAKIXa TEI.EJMIONE. has boon variously and vaguely exj)laii)od by most authors. It will not be necessary for nie to reea[)itulate the several deserip- tions and solutions of this phenomenon, as the novel experi- ment about to be detailed will embrace substantially the whole subject. About a year since, while exhibiting to a cla.ss the vibration of these bars by heat, it became inciuiveiiient to prolong the ex- j)eriment, as the vil)ration ceases as .>^oon as the temperature of the bar is somewhat reduced, and 1 was induced to .seek for some method by which the vibratory motion could l)c produced and continued at i)leasure without the trouble of reheating the bars for each trial. Ai'ter various fruith'ss etforts, [obtained a most beautiful result by using the heating power of a galvanic Fitj. 02. current Fig. 62 shows the mode of ])erforming the experi- ment with the battery. .V ;nid ]? arc the two forms usually given to Trevelyan's bars, which, when to be vibrated by the action of heat, are made of brass, aiul weighing from one to two liound.s, and after being sufTiciently heated are placed u])on a cold block of lead, as seen in lig. iS'.]. The two bars may be ])laccd u])on the same block, though the vibrations are apt to interfere when two are used. When the Iwirs are to vibrate by the galvanic current, they may bi; ot the same size and form a3 shown, and of any kind of metal — brass, or cojjper, or iron, how- ever, seeniing to be most convenient. One or both of the bars may be ])laced at once, without reference to temperature, u])on the stand, as in fig. 62, the bars resting upon metallic rails E F, trevp:lyan' s experiment. 115 which latter are made to communicate each witli the poles of a galvanic battery of some conHiderable heating power. Two j)airs of Daniell's, of Smoe's, or of Grove's battery of large size are sufTicient. Tiie battery I em])loy consists of two pairs of Grove's, with ])lat!nuin plates four iiiclies scjuare. 'J'he vibration will ])rocccd with great ra}>idity as long as the galvanic current is sustained. In lig. 68 one ]w>le of the Ijattery is connected with the metallic block, and the other pole with mercury in a little cavity in the centre of the vibrating bar. Tlie ex})eriment succeeds much better with the rails as in fig. 02, and quite a number of bars may be kept in mo+i(>;i by increasing the number of rails, and l)assing the current from one to the other through the bars rest- ing upon them. Fig. 63. The rails are best made of brass wire, or a strip of sheet brass, though other metals will answer — the harder metals which do not oxidate readily, however, being i)referred. A soft metal, like lead, is not so favorable to the vibrations in this experi- ment, although in Trcvclyan's (X])crimcnt lead seems to be almost the only metal that will answer to supi)ort the bar, which is usually made of brass. Prof. Graham and other authors have attributed the vibration of Trcvclyan's bars to the repulsion between heated bodies, and others have classed the jihenomenon with the s|iheroidal state of heated bodies. I do not consider that any repulsive action is manifested or necessary in either of these cases, nor do 1 know of any instance in which a repulsion has been proved between heated bodies. It is obvious some other solution is required for this curious phenomenon, and it appears to me that the motion 116 TUK HI'EAKIXfl 'IKI-KI'lIONK. is due to an expansion of the metallic hlock at the jioiiit of con- tact, and, \i[Ht\i this supposition, it api)ears plainly why a block of lead is rcipiired. That is, a metal of low conductinj^ power and high expansibility is necessary, and lead answers these con- ditions best In a fiiture communication I will analyze this matter and explain more fully. The size of the bars may be very nnich increased when the galvanic current is enij)loyed, and some curious motions are ob- served when long and large cylinders of metal are used. If they are not exactly balanced, which is almost always the case, they commence a slow rolling back and forth, until finally they roll entirely over, and if the rails were made ^-ery long they would Fig. G4. go on over the whole length. .\n inclination of the rails is re- quired in this case, but it may be so slight as not to be jicrcep- tible to the eye. If a long rod of some weight l)e placed across one of the bars, as shown in fig. 04, the vibrations will become longer, and by way of amusement I have illustrated this with a galvanic see-saw, as it may be termed. It is well hr.own that where mere contact (without metallic continuity) is made by metals conveying the galvanic current, the metals become most heated at the ])oints of contact, and if the current be frequently broken the heat at these points is still more augmented. It is for this reason we are able to use various MOLKCULAR ACTION OF MAGXKTIC ]iOJ)IES. 117 kinds of metals for the experiment, witliout reference t( tlieir conducting powers and expansibilities. VIBRATORY MOVEMENTS AN'l) MOLKCULAK EFFECTS DETER- MINED IN' MAGXETIO BODIES liY THE INFLUENCE OF ELEC- TRIC CURRENTS. ^ Ml". Page, an American philosopher, had observed, in 1837, that on bringing a liat spiral, traversed by an eliT-trio cui'rent, near to the jiole of a powerful magnet, a sound is produced. M. Delozen.ic, in France, also succeeded, in 1838, in producing a .sound by revolving a soft iron arnuiturc ra})idlv before the poles of a horseshoe magnet. In 1843, I niy.self remarked that plates or rods of iron give out a v(>ry decided sound when i)laced in the interior of a helix whoso wire is ti'aversed by a powerful olectrio current; l)iit only at the moment when the circuit is closed, and when it is interrupted. Mr. Ga.ssiot, in London, and Mr. Marrian, in IJirniingham, had also maile an analogous experiment in 18-44. Attril)Uting this singular ]ili( nomenon to n change; brouglit abmit by the magnetism in the molecular constitution of the magnetized body, I wc'nt through a great number ot experiments, in order to study this interesting subject. It is above all things im])ortant. in order to obtain a numerous .scries of vibrations, to be provided with a means of interrupting and of completing, many times in a very short space of time, the circuit of which the wire that transmits the current forms a part; in other words, to render a current discontinuous or continuous. With this view, I made use of one of the numerous apparatus called rheotomes, or cut-currents, and which are intended, when place(l ill the circuit, to render a curi-ent discontinuous. One of the most convenient (lig. (I.j) consists of a hoi'i/.ontal rod, carrving two nceiUcs, inserted perpcndiculai'ly and parallel with ' Treatise (111 Kleetl'ieily in Tlienrv uiul rriu'lice, \cl, argentine, and magnetic bodies in general ; but in diilerent degrees for each, 122 THE SPEAKING TEI.El'IION'^. depending on the coorcitiv(! force that opposes the plienom- cnoii. r Wires oC copper, platinum, silver, and, in general, any metals, except the magnetic, do not give forth any Hoiiiid, whether under the influence of transmitted currents, or under that of ambient currents, such .as the currents that traverse the convoluti; 'is of a wire coiled into a helix around a bobliin. Tiio sound t^.at is produced wlien a discontinuous electric current is made to pass in an iron wire, explains a fact that had been for a long ])criod observed, and had been described as far back as 17S5, by the Canon (Jottoin de Coma, a neighbor and a contemporary of Volta, This fact is, that an iron wire of at li-ast ten yards in longtli, when stn^tchcd in tiic ojien air, spontaneously gives foith a sound under the inlluence of certain variations in the state of the atmosj)liere. The circumstances that accompany, as well as those that favor the production of the phenomenon, demonstrate that it must be attributed to the transmission of atmospheric electricity. This transmission, in fact, does not <}ccur in a continuous manner, like that of a current, but rather by a series of discharges. Now, Mr. Beatson lias demonstrated that the ilischarge of a Leyden jar through an iron wire causes this wire to produce a sound, provided i: does not occur too suddenly, but is a little retarded by passaj/e llirough a moist conductor, such as a wet string. The sounds given out by iron wire and by magnetic bodies, under the circumstances that we have been describing, seem to in- dicate, in an evident manner, that magnetism produced by the in- fluence of an exterior current, as well as by the direct transmis- sion of a current, determines in them a niodirication in the ar- rangement of their particles, that is to sa\', in their molecular constitution. This modification ceases and is constantly pro- duced again by the efTect of the discontinuity of the current; whence results the pi-oduction of a series of vibrations, and con- sequently different sounds. A gi'eat number of observations, made by different philoso- phers, have in fact demonstrated in a direct manner the influence JOULKS EXI'KUIMKN'I-S. 128 of iiiftgnetizati(jn u[)on tlio luoloculiir properties of maf^netic bodies. M. de Wertlicim, in an extensive work on tlie elasticity of nietiils, liiul iilri'ady observed, tliat niaf,Mi('ti/cation produced by means of a helix wliose wire is traversed liy tbt; electric current produces a ditninution in tbe eoeflicient of elasticity in iron wire and even in steel; a diminutio!i wliicli, in tlie latter at least, re- mains in part even after tlie interruption of llio current .\[. ! Guilleniin has also remarked moic recently, that a bar of soft ( iron, fixed i)y one of its extremities whilst the other is free, and) ■which, instead of remaining hori/ontid, is curved by thoeilect] of its own weight, or by that of a small ailditioiiid weight, im- mediately rai.-^es itself, when the current is made to pass in the ^ wire of a helix with which it is surrounded, wdiieli helix is itself raised up with the bar, all the movements of which it follows, , since it is coiled around it This cxpcritncMit possc.-ises this im- ])ortant feature.— it shows the magnetization determines a modi- , fication in the molecular state of iron ; for it cannot be exiilained I by a mechanical action, which could only occur if the helix is independent of the l)!ir. , Furthermore, an Knglish philosopher, Mr. .loule, succeede'l in determining the inlluence that magnetization can exercise over the dimensions of bodies. By placing a soft iron b; r in a well closed tube, filled with water and surmounted by a caiiillary tube, he lir.st satisfied himself that this bar experienced no varia- tion of volume when it was magnetized ly means of a powerful electric current, which traversed all the coils of an enveloping helix. In fact, the least variation of volume would have b(>eu detected by a chang(! of the level of the water in tlu! caiiillary tube; now not the .slightest is observed, however powerful the magnetization may be. 'Phis result is in accordance with what M. (ray-Iais.'Jae had discoverecl by other methods, and with what M. Wertlicim had also obtained by operating very nearly in the same manner as Mr. Joule. But if the total volume is not altered, it is not the same for the relative dimensions of the bar, which, under the influence of magnetization, experiences m increase in length at the same time as it does a diminution in 124 THE SI'KAKING TELEPHONE. diameter, at least within certain limits. It was hj means of a very delicate apparatus, similar to the instrument employed in measuring the dilation of si^lids, that Mr. Joule discovered that a soft iron bar experience,-! a decided elongation, whicli is about sTTTj^-u^th of its total length, at the moment when the current by which it is magnetized i^ established, and a shortening at the moment when it is interrupted. The shortening is less than the lengthening, because the bar always ret^uns a certain degree of magnetism. It would appear that the lengthening is propor- 1 tional, in a given bar, to the square of the intensity of the magnetism that is developed in it. When W(^ make use of iron wires instead of bars, it may hap])en that it is a shortening, ami not a lengthening, that is obtained at the moment of magnetiza- tion. This change in the nature of the elTect is observed wiien th(^ degree of tension to which the wire is subjected exceeds a certain limit. Thus an iron wire. 12.^ inches in length by tI- inch in diameter, di.stinctly lengthens under the influence of the nuignetistn, so long as it is not exi)oscd to a greater tension than 772 lbs. ; Imt the less so. however, as it approaches nearer to this tension. Setting out fn^m this limit, and for increasing tensions, which in one cxjieriment W';r(! carried up to 17i'i4: lbs., the wire was con- stantly seen to shorten at the moniiMit wlien it was magnetized. j Tension exercises no influence over highly tempered steel; so there is never any elongation, but merely a shortening, which I commences when the force of the current e\c(;eds that which is ' nccessai'v to magnetize tiie bar to saturation. •* M. Wertheim, on ins part, at the close of long and minute researches, snc<;eeded in analyzing the mechanical clTects that are manifested in magnetization, lie found that, when an iron bar is lixed bv one ol its extivmities, and the bob])in is so ])!ai'(id that its axis coincides with that of the bar, no lateral movement is observed, but merely a very small elongation, which rarely excecMls .(l()07'i' inch. This elongation is the gn-atcM- as the bol)- biu is situated nearer to th(^ free exti'cmity of the bar, and dim- inishes in ]irl)iii, tlic elongation still remains; but it is accompanied bv a lateral movement in the direction of the radius of the bobbin. The T)obbiii that was employed by M. Wertheini was 9.8-i inches lim^-, and 7 inches in interior diameter; gla.sses of a magnifying powei- of about 20 diameters, and mntaining two steel wins, were used to measure the elongation ami the lateral displace- ment. This displacement, or, what comes to the same thing, the versed sine of the curvatun^ of the bar, measui'cd at its <'xtrcniity, was determined for different intensities of current; and it ap- peared that it was in general ])roportional to this intensity, but it A'aried foi- each position of the bar in the interior of the bob- bin. However it may be, we are able to lind for each of the.se jiositions the mechanical equivalent of the unit of the intensity of the I'urrcnt, namely, the weight which, when apjilied at the extremity of the bar, would produce the .same versed sine. Thus, for example, by calling the length of the part of the 'radius, comprised between the axis of the bar and the axis of the bobbin D, the vcM'sed h\uv, of tlu^ curve /,' the w(;ight that would ])roducii tlu! .same ver.sed sine P, the following results have been obtainc— ."ill. 1, ./■ .•i;th>i fwi. .■t.itti;)a " 1,5-J4U " 1 J' ; n^.'.i'i irrw. ' 41. 'Ji! ! Ii2.r>7 1 Tr. 1 / .■J.'i^'i fcut. l,.Vi::i •' .y.'itiu " r .W.Ml jirs. •2:1.04 1-2.55 Tr. •> 3 We calculate P from the formula P. l^'L^ C, in which /'is the versed sine of the curvature, g the coeflicient of elasticity, which is 27,122,653 Ib.s. avoinlupois perscpiare inch for soft iron, i and c tlu! width and thiekne.s.s of the bar, and L its length from it8 lixcd point to its free extremity. From the j)receding table we deduce the value of the mechanical forct's that are between 126 THE SPEAKING TELEPHOXE. tliem : iov D=80, as 100 : 41.71 : 22.81 : find for D=50, as 100 : 40.50 : 23.34. So we may conclude, since the musses of the tliree bars are together as 100 : 40.5 : 25.5, tliat the elfcct, which is here an attraction, is jtroportional to the mass of iron u[)ou whidi tlie curnnit is actinjj-. We. in like manner, lind that it is proportional to the intensity of the current; which would render it an easy manner to construct upon tliis principle a \ ■^ry sensible galvanometer, by employing a prismatic b 'ibi. .da wide and thin iron band. Thus, all the experiments that we have been relating lead us to recognize that there is produced, by the effect of magnetiza- tion, a mechanical traction, due to a longitudinal component and to a transverse component: that tiic latter becomes null when the l)ar is situated in the centre of the helix ; that they are both in-oportional to the intensity of the current and to the mass of the iron. It is a more difficult matter to verify the elfeet of the trans- mitted current than that of the cxtei'ior current, by which nuig- nctizaiion is producecl. In fact, in tiie former ca.se, the mechan- ical effect of the current is very dillicultly separated from its calorific effect. However, it follows, from auxnv of Mr. Beatsnu's experiments, that an inm win^, at the instant it is jmt int ihi. circuit, ajtpears to undergo a small sudden expansion, an. very distinct from the dilatation that results in it, as Ut ..".cr metals, from the heating produced by the passage of the curren, These mechanical effects being once well studii'd, we can re- turn, with greater knowledge of the cause, to the study itself of the sounds that accompany !.>oth magnetization and the trans- mission of currents. M. Wcrtlieim has in a ])erfectly accuiate manner vcrilied the oxistence of a longitudinal sound in an iron or .steel bar when jilai'cil in the centre of helices traversed by discontinuous cur- rents. This sound, which is similar to that produced I' ; ■ iction, is due, as is proved by direct experiment, to vibration- ;■ uaUy made in the direction of the axis. AVith wires sub.stiti.te i for bars the effects are the same, except that, when the tension WKKTHEIM S KESEARCUES. 127 diminishes, wc hear, in addition to the longitudinal sound, a very j)eculiai' metallic noise, wliicii sccuis to run along the wire, as well as other peculiar noises. Witli transmitted currents we also hear tlus longitudinal .^^ound; and it remains nearly the same in intensity whether the current traver.- all ]>lace themselves ])arallel to the axis, that is to say, vertieally, and the fdings Urrange themselves iu small 128 THE Sl'KAKING TELEPHONE. clonpratpd pyramids in the diroction of tlip axif, which destroy themselves ami rapidly I'oriu a,iraiii wlieu tiie current is interniit- teiit. The action of tlie helix, therefore, u\ym filings, consists in grouping them under the forms of lilaments j)arallel to the axis — iihunents which gravity alone prevents being as long as the helix itself. This exiieriment succeeds equally well with inipal[ial)le ])0\vder of iron as with tilings; it succeeds erpially well with powder of nickel and cobalt; only if the current that traverses the helix is discontinuous, very diirerentefTects are observed witli each of these thn>e metals — effects that depend, as to their ]iar- tieular nature, upon the greater or less numl)er of interrujitions which the current experiences in a given time. The pyramids of filings are at their maximum of height wlieii the disk that sus- tains them is in the middle of thi' helix. They turn under the iidluence of discontinuous currents, jiroviding the succession of >^hese currents is not too rapid, so that there are not more than 60 or 80 in a second. With 100 there is no longer any eiVeet. The.sc difl'erences are imlircctlv due to the fact that the softest iron lias still some coercitive force, and that it requires a certain tinu! for magnetizing and demagnetizing. By comparing under this relation iron, nickel and cobalt, all reduced to an impalj)able powder, and prepared by hydrogen, we lind that nickel still mani- fests movements for a velocity of succession of currents, at which iron ceases to manifest any; and that cobalt, on the contrary, ceases to manifest them before iron, which is quite iri accordaiiee with what we know of the co(M'citive force of these three metals. The following is an experiment of Mr. Groves, which demon- strates in an elegant manner this tendency of the ])artieles of magnetic bodies to group tlu'iiiselve.s, under the influence of magnetization, in a longitudinal or axial direction. A glass tube, closed at its two extremities by glass ])lates, is filled with ■water holding in suspension line jiowder of a magnetic oxide of iron. On looking at distant objects llirough this tube, we per- ceive that a considerable ])roportioii of the light is intermitted by the irregular dis.seiiiination of the solid particles in the water. But, as soon as an electric current traverses the wire of a helix, GROVE S EXPERIMENTS. 12i> -with which the tube is suiToiindcd, tlic particles of oxide arrange themselves in a regular nml syminetrical iiiauner, so as to allow the larger jjroportion of tiie light to pass. The particles in this case are not small fragments of iron wire, art i Ilea 11 y disaggre- gated from a more cimsidcrabh^ mass, but iron precipitated chemically, and conseciucntlv in its natural molecular .state, such as constitutes a solid bodv bv its aggregation. This dis])osition of the particles of iron and of magnetic bodies to approach each other in the transvei'se direction, and to extend in the longitudinal diri-ction, under the influence of an exterior magnetization, which is probaldy due to the form of tlie element irv molecules, and to the manner in which they are polari/.ed, is now estal)lislie(l in an irrefragable manner by direct and jiurely mechanical ])ro(ifs. It is easy to see that it accounts in the clearest manner for the production of sound in a bur or a wire sul)jectcd to the influence of the intermittent cui'rcnt of the helix. The jinrticdes contend- ing against cohesion arrange themselves in the longitudinal direction when the current acts, and return to their primitive position as soon as it ceases: thert; follows from this a .', these liht- ments, instead of remaining rectilinear, join together hy their two edges, and envelop the sin-face of the wire, forming around it a cloi^cd curve, like a s))eeies of envelope composed of rings that cover each other and are jiressed against each other. Now, the arrangement assumed hy the particles of iron tilings round any conducting wire, iron as well as every other metal, when it trans- mits a cuiTcnt, ought to he in like manner assunicd hy the mole- cules of the very surface of a soft iron v»'ire itself traversed by a current, under the influence of the current transmitted by the en- tire mass of the wire. This, also, is equally demonstrated by the mechanical effects studied by Joule and Beatson, It follow.s, therefore, that when the transmitted current is intermittent the particles of the surface of the iron wire oscillate between the transverse position and their natural position, and that there is consequentlv. a production of vibration.s. These oscillations ought to be the more easy, and consequently the vilirations more pow(M'ful, as the iron is .softer; with hardened iron, and especially with steel, there is a greater resistance to be overcome ; DK LA KIVKS HKSEAKCIIES. 131 thus the offcft is loss sensible. If tlic wire thnt transmits the (liscoiiliiuiouri current is itself traversed hy a continuous current moving in the same direction as the discontinuous one, the oscil- latory movement oudit to In- auuuUeil, or at least notably di- minished, since the trausmissiou of the continuous current im- ])rcsses npon the ])articles in a ])enuancnt manner the ])Ositiou which the passage of the discontinuous current tends to give them in a temporary maTiner. Thus the sound in this ease would com- ])letely disa])])ear or notablv dimiuisli. If the wuv. is of steel or of well hardened iron, the continuous current is, on the contrary, favorable, by its presence, to the oscillating action of the discon- tinuous current, because it deranges the particles from their nor- mal position, without, however, being able couipletcly to im])ress ujion tiiem the transverse direction, on account of the too great resistance they op})ose to a displacement, which is easily brought about in soft iron. The two currents united pro, \vc perceive tliattlic iron liliugri arc attracted upon its two edges, which have also an opi)Ositc j)olarity. The detailed explanation that we have given of the molecular ])hcnoniena. which, in magnetic hodies, aceoiiipany the action of currents both exterior as well as interior, llnds a further con- firmation in the observMtion of several facts of different kinds. Thus I have remarked that ]>ermanent magnetization, whether impressed upon a soft iron rod by the action of an envclo[)ing helix, or by the action of a jiowcrful electro-magnet, increases, in a very decided manner, the intensity of the .sounds that are given out by this rod, when traversed by a discontinuous cur- rent. This reinforcement is, in fact, evidently due to the conflict that is established between the longitudinal direction that is impressed upon the particles of iron by the influence of the magnetization, and tlie transverse direction that the passage of the current t(Mids to give to them. The oscilhitions of tlie j)articles ought neces- sarily to have greater amplitude, since they occur between more extreme positions. The effect is more decided with .soft iron rods than with tiiosc of steel, and especially tempered steel. Mr. Beatson arriveil at a similar rcsiUt by quite another method. lie observed, that if a continuous current tra\er.-;es a wire, and if, at the same time it is subjected to the action of a helix in which a discontinuous eurivnt is passing, the wire will undergo a series of contractions and ex[)ansioiis which become inappreci- able, if the continuous current ceases to be transmitted, even when the helix continues to act in the same maimer. The autlun' drew from this the same conclusion that I had deduced from the sonorous effects, namely, that the action of the helix impresses ui)on the particles of iron an opposite state to that which is produced by tlu; transmitted current, and that one of these actions has the tendency to invert the arrangement which the other tends to establish. A very curious fact is that magnetization tends to impress MAGGI.S HEAT EXI'KUIMKNTS. 133 upon tlio particles of soft iron an arrangement similar to that which they jtosscss in tempered steel, even before it is magnetized. What conlirms the correctness of this remark is, that tlie S(jund which magnetized soft iron gives out under the action of the transmitted current, is not only more powerful than it is when then; is no magnetization, l)\it, it also acquires a peculiar diy tone, which makes it resemble that which steel gives out with- out being magnetized. The very remarkable influence of tension, which, beyond a certain limit, diminishes in soft iron wires their aptitude to give sounds, is a further consequence of our explanation. In fact, the molecules, by the elTect of tension, undergo a permanent derangement in their normal ])()sition, and are consequently found cripplcil in their movements, and arc no longer able, under the influence of exterior or interior causes, to execute the oscillatory movi^ments, and consequently the vibrations which constitute the >"und. Two facts, of a eliaractcr altogether different from the })r(>ceil- ing, still further show that the magnetization of iron is always attended by a molecular change in its mass. The lirst of these facts was discovered by Mr. Grove. It is, that an armature of soft iron experiences an elevation of tem- perature of several degrees when it is magnetized and demaguet izcd several times successively by means of an electro-magnet, or even of an ordinary magnet set in rotation in front of it. CobaU and nickel ])rescnt the same phenomenon, but in a somewhat slighter degnn; ; whilst non-magnetic metals, placed under exactly the same circumstances do not ])resent the slightest traces of calorific effects. Tiiis exjJerinuMit can only In; explained by admitting that the development of heat arises from the mole- cular changes whicli accompany magnetization and demagneti- zation. The sccoml fact, which is no l(>ss inq)ortant, is due to Dr. ^raggi. of ViM'ona, who ])rovcd that a circular ]ilate of very homogeneous soft iron condu(>ts heat with more facility in one direction tlian in the other when it is niagn(-tize(l by a powerful electro-magnet ; whilst, when it is in the natural state, its conduct- 134 TIIK SPEAKING TELEPHONE. ibilitv is tlic same in all directions, and, consequently, jieHectly uuilnrni. The j)late is covered with a tiiiii coating' of wax melted with oil, and the heat arrives at its centre hy a tuhe that tra- verses it, and in the interior of which the vapor of hoiling water is i)assing. Tin; ])late is jilaet'd horizontally on the two poles of a jiowerful eleetro-ina^niet, several insulatiiijr cards jire- vcnting contact between it and the iron of tlie electro-magnet. So long as it remains in its natural state, the curves that bound the melted wax assume the circular form which inrfnl is the magnetism it re- covers. Thus, a bar, that made a needle deviate 00^, having been brought by a sueeession of discharges to exercise no devia- tion beyond 0°, gave li° on falling from a height of 12.8 feet, 15° SO'on falling from a height of lo.O feet, a ' 21' on falling from a height of (i.l feet* This new polarit in the same direction a.s the primitive one. Even when, by destroying the primitive magnetization of the bar, we have actually imparted to it a new one in a contrary di- rection, we lind on letting it fall npoii the ])avement that we re- .'^tore to it thelirst that is jiossessed. ^I. Marianini would be dis- ])oS(>d to believe from this expiu'iment and other similar ones, that the bar had retained its fonner magnetization while still acquir- ing the contrary one, which ncntralizcMl the elT(>ct, of the Iirst and even surpasses I it ; and the shock merelv dcstnivcd the second, either in whole or in part, which ])ci'niittcd the former to reap- pear. Fle.xion, friction, heat, or an electric discharge traversing the iron directly, niay take the place of the shock, particularly when very line wires are iiMjuestion. The action that is exercised by an instantaneons discharge through the wire of a helix iipon a body already magnetized, in- creases or diminishes the magnetism of this body according to the direction in which it is sent ; but this increase oi- diniiimtioii isthe less sensible as tlit; iron is more magnetized. In any case, a given instantaneous current produces ]iroporti()natcly more elleet when it is maile to act with a view of diminishing the polarity in the magnetized bodies than when it is made to act with a view of increasing it. M. .Marianini, in order to ex])laiu the results of these experi- ments, admits a dillerence between what he calls polarity and MAUIAMM S KXI'KUIMRNTH. 187 magnotism. Thus, the sumo Jii;i<(iM't, ulthoiigli doprivcil of polarity, may very readily ivUiiumagiiolisin, wlieii magiit'tixcd ut one time in two contrary directions with iiii equal force. Wo must tli(>n su|)|)f)so that contrary magnetic; systems ])rodueing e((uilil)rium are able to exist in iron, and that exterior forces, such as a current or o, nieehanieal action, do not act with the same energy u))on tlio o])|)()sito systems. This opinion, which doea not as yet appear to us to rest upon facts sullieiently numerous, has, however, nothing in it that is inadmissil)le ; nothing, in fact, oj)poses there being in thesamo liar a certain numlierof ij.article.s arrange(l so as to produce a m; uiietization in a certain direction, and others so as to prcMluce magnetization in the op{)osite di- rection ; as, for example, the interior particles m.'iy l)e found to liavo in this r(>spect an arrangement the op|)osito of those on the surfaces; and that such exterior action operates proportionately with greater force nj)on the one than upon the other. This jKjint Would need to be made clear by further observations, and especially by comparative ex[)eriinents made upon bars of dif- ferent forms and different dimensions — upon liollow and solid cylinders, forexamjile. Rut if some doubts still remain upon the conclusions that M. Marianini has drawn from iiis experi- ments, there are not any iijion the new proof which they liring in favor of the connection that exists between magnetic and mole- cular phenomena. Tlic(bfTerent degrees of ai)titudeae(piired by iron under the influence of certain actions, of becoming more easily magneti/,cd in one direction tlian in thoother, arealNiuite in har- mony with tlio disposition with which the [)articles of Ixxhes are endoW(>d toari'angc; themselves more easily in one direction than in another. 'I'his los.s of ajititude, after the multiplied repetition of the contrary actions, corresponds with the inditlerenee to arrange themselves in one manner or the other, which is fin.ally presented by the j)articles of bodies, aft(>r having experienced numerous dcranw'nients in different directions, i Finallv the RMuarkable iWi' liiivu II rcniiirkiil)li'. cxiiinplu of tliU in tlu^ frii/ility |)rcs('iit('il by iron wlieii it has lici'ii for II loii|^ tiiiio HuliJL-ctfJ to riipid mid I'lvciuuia viliriitious, us arc tlir axles (if loc'oiucitivus. 138 THE SPEAKING TELEPHONE. effects of shock, flexion, heat, in fact, of all tliosc actions that change tlie relative position of the particles, ctviiie in supjiort of the relation tliat we liav(! endeavored to establish. Tlic whole of the nuigneto-molecular phenomena that we have been studying, lead us t( > believe that the magnetization of a body is due to a ]iartieular arrangement of its molecules, origin- ally endowed with magnetic virtue; Init whicli, in the natural state, are so arranged, that the magnetism of the body that they constitute is not a])])ai'ent. Magnetization would therefore con- sist in disturl)ing tliis state of e(|uilil)rium, or in giving to the par- ticles an arrangement that malce.; manifest the prop('rt3' with which they are endowed, and not in devcIo])iugit in tiieni. The coerci- tivc force would be the resistance of the molecules to change their relative i)ositii)iis. ileat, by facihtating the movenwnt of tlic particles in respect to each otiier, diminishes, as indeed does every mechanical action, this resistance, that is to say, the coerci- tive force. I'here remains an important question to be resolved. Are mechanical or otlier actions — ilisturl)ers, as they are, of the electri- cal state — al)le of tliem.selves to give rise to magnetism? or do they only facilitate the action passed through the spiral the discontinuous current of u galvanic battery. Other physicists, and especially Delezenne, Beatson, Marriau, Alatteucci, Dc la Rive, and Wertheim, in Ibilowiiig up the dis- covery, have sliown us that it is tlic intcrrnptc s:une time (^n the wire. Tilt! method wiiicli we ai'c now about to describe, and which the writer happened to discovei' accidentally in the fall of 1854, possesses the advantage of generalizing matters, as it shows that all metals can, under certain onditions, be made to emit tones; there are also other consid -atious which render it interesting as regards its connection with the theory of electricity. This method is based u[)on tlu^ intei'ruptions of a battery curnMit, although ill reality it is not the latter, but rather the induced (/urrents ]U'oduced by tlie intci'ruptions that nnist bo considered as the generator of the tones. In place also of bars or wires as 1 .1. C. Pn(t)reiulorf. I'i)if(,'i'udi)rf 8 .Viinuluii, .Moviii., p. l!»;i. Mdimtsburichti'ii dor Aoiul. Miirz, IKnii. 140 THE SPEAKING TELEPHONE. heretofore used for producing the tones, tuljes formed of sheet metal are substituted, and surround the coils through which the current is passed. The writer u.sed in his experiments coils five inches in length and about one and one eighth inches in diameter. Both wires of the coils were connected, .so tiiat their united length was about 100 feet; the diameter of the wire was 1.4 millimetres. The coils were maintained in a vertical i)osition by means of a .^tand provided for the purpo.se, and so ])luced that tlie lower ends could be connected to the battciy, which, as a rule, consisted simply of a single Grove cell. The tubes to be examined, which were about five inches long and from two to four inches in diameter, wert' then [)laccd over the coils. Some of them were left entirely o})en, sonu; closed by .soldering, and others bent together so that the edges just touched each t)ther. The ma- terial of the tubes consisted of platinum, copper, silver, tin, brass, zinc lead ami iron. A Wagcner hammer of peculiar construction, so as to dead(>n the noise of its own vibrations, and thus prevent it from interfer- ing with the investigations, was u.-;e(l fur interrupting the current From the experiments made with this ajtjjaratus it has been found that ikjiic of the metals, except iron, can be made to emit tones when formed into either open or completely closed tubes and placed over the eoils. If, liowever, th(> edges of the tubes just touch each otliei', then all metals can be made to emit a vcrv auililile lone, whicli will vary in louilness and ipiality of .-^ound with the dimensions of the tubes, the elasticity and qual- ity of the material employed, the strength of the current, and certain other minor considerations that will readily suggest themst'lve.'*. Iron is distinguished from the other metals by the fact, tlue no iloubt to its magnetic properties, that it giv(>s a crackling tone both whi'u matle into an open tube which surrounds the coil, and also when jilaced alongside of it. The tone in this case is similar to that heretofore notieed in sheet iron when laid in the coil, but it is much weaker than that heard when the edges of TONES PKODUCED HY ELECTKIUITY. 141 the tube come in contact In the latter case it seems as though a second tone appears with the former one. The sounds obtained in this manner from metallic tubes whose edges just come in contact with each other, arc evidently produced l)j the induced current generated in the mass of the tubes by tlie action of the intermittent current in the coil. They must evidently, therefore, become strong(>r or weaker as the con- ditions which give rise to them render the induced current stronger or weaker. For example, they are increased when iron wires are placed in tlie coils, as was done in the experiments made by the writer. They are also increased, but in a smaller degree, when tlie coil is connected with a condenser, which was also done in all of these experiments. The weakening of the tones. iio\v(>vcr, may be still more strikingly shown. For this pui'posc it is only necessary to place bclwccn the tube producing the tone and the induction coil another metallic tube, comiilctdy closed and of somewhat smaller diameter. As somh as this is done, the tone of the wider tube ceases inst;. , ly, and when the smaller tube is withdrawn again the tone lunence-; it once. Even two tubes of dill'ercnt diameti • - capable alone of g' . mg out tones will show this weakening. Imu if placed simultaneously one within the otiicr around the coil, the\ do not inli fere with each other. In ])lace of the smaller closed tube, which, for example, may consist of zinc or any other non-magnetic metal an open iron tube may bo substituted. In this case also the action depends u]ion the length and thickness of the metal, and weakens or destroys the tones accordingly; not, however, becaust'ai uluccd current is formed in it as in the ca.se of tlu> clo.sed y.\v- tube, but becau.se it becomes magnetized by the a(!tion of the I'oil, just a.s the c(jre does, and the effects of the coil and core consequently oppose each other. The ]n-oof of the connection of the tones with the induced current, if additional proof is nece.s,sary, is still further shown by the fact that they are quite iadependent of the diameter of the 142 THE SPEAKING TELEl'IIOXE. tubes. The writer has obtained tones from tubes of two, four, and ei])ortion between the length and diameter of the tubes. With projiortionatc length, a hollow evlimler of any diauietcr whatever would obviously be forced by tia; action of a single cell (if battery to emit t(mes just as wi-U as a tube of onl}- an inch in diameter Now, whil(> it may be considered sufficiently evident that the tones in question owe their origin to the imlueeil currents whicii are produced in the tubes ])arallelly with the convoluti(ms of the coil, and in this respect therefore correspond to the tones gener- ated in .steel or iron wires when an intermittent euiTcnt is passed directly through the latter, we must by no means conclude that they ai-e the result of a juolecular action extending throughout the entire mass of the metal, as is certainly the ca.se when iron wires or open iron tubes arc n«cd. On the contrary, as the writer is fully convinceil, the development of tones lirst noticed by him. has its origin at the points where the edges of the tubes touch each other, and that, in consequence of this, slight concus- sions occur which set the tubes to vibrating and thus give out tones. The tones, moreover, are only a secondary phenomenon, and may entirely fail wlien the material of which the tubes are made possesses but little elasticity, as, for instance, when lead is u.-^ed. 'riic real part of th(> acoustical ])henomenon lies in the'dull sound or kind of ticking, .somewhat similar to that of a watch, which is heard at the points where the edges come in contact .simultane- ously with the strokes of the vibrating hammer. It is consequently this ticking alone, and not the tone produc- tion, whose investigation properly comes witliin the province of electrical science, an ' which I eonser|uently made the especial subject of .study, but U]) to the present time I am obligeil to sav I have not yet succf ded iu bringing about a complete solution of the problem. TONES PRODUCED BY KLECTRICITY. 143 The tickinf^ tone is not anrlihlo in a tube whose edges have been soldered, and thus prol)ab]y made to resemble more nearly a hollow oast-ii'on cylinder. ICven a soldered t\xl)e. which has l)een so nearly cut in two that oidy a ])orti()n of metal of about a line in width remains, is found to give no ticking sound nnder the conditions I employed. This shows that a certain se]iaration of the cdgc.^s is required for the production of the sound; it is furthermore perfectly clear that the adja(!ent edges of the tnbe do not come in so close contact as the ]iaiticles within the ma.ss, and is also proven by phenomena in other provinces of physical science. With ap- parently the very best contact, also, wc must admit the exist- ence of a thin air stratum between the edges of the tube, the same as exists even in the dark centre of Newton's rings. The influence which distance between the edges of the tubes has on the ticking is shown by the fact that, the more the edges are pressed together the greater is the decrease in the sound, and it is not improbable therefore that if the compression were in- creased with force sufficient to press tlie partii'lesof metal firmly against each other, the scmnd could be eutii'clv destroyed. On the other hand, again, if a loud sound is wanted it is necessary to make the edges just touch each other loosely. It might be thought an increase of ].ressui'e would increase the number of contact jioints also, and in this manner cuuse the decrease in the strength of the sound. This coidd only have been the case when I caused greater portions of the edges of the tubes that were not quite parallel to a])proa('h each other, so that in general such a conclusion will hardiv be found to hold good. It has furthermore been found that when a short piece of wire or a sewing needle is placed between the edges of the tube, the ticking then bccoiues very loud, but decreases in like manner with increased pressure, although the needle is never made to touf^h at all points. Portions of the tube edges may also be in close metallic con- tact without tlu! entire disajipcarancc of th(> ticking if ouly other portions make but slight contact with each other. Hence tubes 144 THE SPEAKING TELEPHONE. which have hoeii partially cut in two, like those previously meutioned, will oonuuonce to give out sounds if a needle or wedge-sliape })iece of luetai is inserted in the slit. This exj)l;tins a pheuonienou which is observed with tin. When a sheet of this metal is bent around the induction coil and its edges are brought close to each other, they immediately become fastened together as if soldered, and yet the ticking continues to be heard exceed- ingly well, if, however, the neighboring edges are melted together with a spirit flame or soldering iron, the soimd ceases. The principal rpiestion in this examination is of course this: Wiiat causes the tickingsound at the divided edges? On lirst consideration it might be attributed to the ]iassage of sparks, but this certainly is not the origin of the sound. Sparks may gener- ally be .'Jeen by separating the edges of the tubes from each other at the moment the hammer interrupts the l)attery current. Tliey are also noticed, but in a lesser degree, with tubes which have been partially cut in two, when the wedge is allowed to drop into the opening. But so long as tlie edges remain quietly near each other no spark is observed, even in perfect darknes.s and yet .the ticking continues all the time without the slightest inter- Iruption. I further placed the induction coil with tiie metallic 'tube under the exhausted receiver of an air ])mnp, but even there the ticking was heard without the least .s])ark being visible between the edges of the tube. The sparks, moreover, ])ossess an exceedingly low potential, but this is not to be wondered at when we consider tliat they are produced in a metallic conductor of only a few inches in length. With ca.sily fusible metals, such as tin for example, sparks ar(> often seen to be projected for a distance of several lines, but these caimot be considered as genuin(! electrical sparks ; they are cau.sed rather by the projection of particles of melted and glow- ing metal, and their direction also is generally contrary to that of the electrical current, being sometimes towards one side and sometimes towards another. In any case, however, they can never be real electrical sparks, since the electrical ])otential of the current, as already stated, is too low for their production. It TOXES PHODL'CED BY ELECTRICITY. 145 made no difftM-enco how near I brought tlic edges togethei- witli- out causing alisoliite contact, I could never preceive the i)as- sage of sparks between them. The sbght space miglit also be closed 1)}' tiie moistened lingers, or the tip of the tongue even might he placed between the edges of tlie tuljes without feeling the sliglite--t sensation. If Sjiarks were the cause of the sound one would naturally suppose it woidd disappear in a (luid conductor, but while maintaining the tube in a horizontal position, 1 have dipped its edges III s])ring v>-ater, and even in diluted sulphuric acid, without being able to perceive any decrease in the sound. When, how- ever, a thin piece of blotting paper, which has l)een saturated with diluted sulphuric acid, is placed hetween the edges, and consecpicntly the metallic contact is broken, the sound disap- jtears. It also disappears with zinc tubes when the edges ai-e so thorougldy amalgamated that drops of mercury remain adhering thereto, obviously, however, l)ecausc perfect metaUic contact i.s thus established. On the other hand, again, the sound did not cease when tho edges wert' highly heated by the flame of a sjiirit lamp, but a decrease in its loudness was certainly n, if wonls themselves cannot he transmitted by electricity ; in other words, if one could not speak at Vienna and make oneself heard in Paris — the thing is practicable, and T will show you how. Imagine that you sjteak against a sensitive plate, so flexible as to lose none of the vibrations jirodueed by the voice, and that this plat(! makes and breaks successively the conununieation with an electric Jiile; you may have at any di.stanee another plate, which will undergo in the .— without the spring, however, making more vibrations on that account. It may be tliat the time is still distant when it will be ])ossible for us to hold a converstition with a friend at a distance, and to distinguish his voice as if he were in the same room with us. Still the probability of success in this has become as great as it was during the important experiments of Xiepce for tlie repro- duction of the natural colors by photography. CnAPTKR A^ GRAY S 'lELKI'lIOXK! ItKSKAUCIIES. * While engaged in studying tbo iihciiouieniuif induced cur- rents, I had noticed a sound pnjceeding fmiii an I'k'ctro-nmgnct connected in tlic secondary circuit of a small Klimukorfr coil, wliicli was at that time in o|icratioii. 'i^liis, of course, was not new (it having hccn ol)serve(l by Page. Henry and others that tho iMiignetization of iron is acconii»anied with sound), hut it helped to direct my mind to the subject of transmitting musical tones telegra|ihieally. Subse([uently I mailo a discovery that ]rd to a thorough investigation of tlio subject, and I have de- vnted my whole time since then to tho study which it suggested. 'riu! circumstance was a.s follows: My nephew was ]ilaying with a small incbiction coil, and, as iio expressed it, was ''taking shocks "for tho amusement of the smaller children. ]Ie Jiad connected one end of tho secondary coil to the zinc bning of the batli full, which was dry at that time, nulding tho other end of tlio coil in liis left hand, ho touched the lining of the tub with tho right. In making contact, hi.s hand would gliile along tlio side for a short distance. At these times 1 noticed a sound pro- ceeding from under his hand at the puint of contact, which seemed to have tiie same jiitch and quality as that of tlu; vibrat- ing elcctrot(jme, which was within hearing. I immetbately took the elcctrodo in my hand, and, repeating th(^ operation, to my astonishment fouml, that by rubliing liard and ra[iidly, 1 could make a much louder sound than tho clectrotome was makhig. I then changed the pitch <^f the vibration, increasing its rapidity, and found that the ])itch of the sound under my hand was also changeil, it still agreeing with that of the vibration. I then moistened mv hand and continued the rubliing, but no sound 1 Experinit'iital Ro.sciirelii's by Elislm (Iniy. Kcml before tlio Arncrioan f^lectri- (Mil Suc'iotv, Miircli 17, is;,';. 152 TIIK SPEAKIXa TELEPHONE. was pri)(lu('('(l so ]impf as mv I'avid roinaincd wpt : Imt as soon as tlic parts ill coiitacl bocaiiu' ilrv tlu> soiiml iva])pear('il. Tlu^ next, sicj) was t<> coiistriicl. a koy lioaivl, with a raiiixo at first of one octave, similar in appearance to llio cut shown in lig. 69, Avliich has two octaves. Each key lias a steel reed or electrotnme, tuned to correspond to its jiosition ill the nuisieal scale. A better understanding of tlie operation of a key and its corresponding clcctrotonic may lu' obtained by re ferrinir to the detached section shown in fur. 70. Fig. 69. a is a steel reed tuned to \'ibratc at a deliiiite rate, correspond- ing to its jiosition ill the scale. One end is I'igidI}' ii-\.ed to the jiost (j. while the other ciid is left free, and is actuatce tiie case when s(3 branclu>s are open at the key jjoints, neither of the batteries is closed unless u, key is tlcprcssed. If now the keys are manipulated, a tune maybe ])laycil which is audible to the jtlayer. When any key is depresse(|, the local battery sets in vibration its corresponding reed, which sounils its own fundamental note according to the law of acoustics. So far the instrunu'nt is an electrical oi-gan, the motive ]iower being electricity instead of ;iii-. The main battery has had no j'art whatcN'cr iti its operation. ]f, however, the mniii circuit is closed by connecting the (lis- taiit end to ground, aur one, owing to tlu; fact that the terminal secondaiy M'av(' is much more inten.^e than tlu; initial. J now held my hand still, and, while T could feel the shock just as distinctly as hefon', theri^ was no audible soiind, proving that the motion was a ncce.ssary condition in its prodnctidii. The seiisatinn when the .sotmd was proiluecil was as though my linger hail sndd(>nly ad- hered to the plate, and then as suddenly let go, producing a sound. The next experiment was with one hundred cells of gravity liattery. I connected one pole to the ])late and held the othei" in my hand, pressing my lingi-r against the jilate and revolving it as before. I inserted a thin [liecc of paper between my lingers and the plate to prevent jiaiid'ul eifects from the current, and my assistant made da.shes with a key in the circuit. T was thus able to notice the eifect of an imjml.-^e of longer duration. When the key closed there was a pen e])tible increase of the friction, so that my finger took a position farther forward on the plate, where it would remain as long as thi^ circiut remained closed. As s(xin as the key was op<'neil my linger suddenly dropped back on the plate, making the same noise I had before heard. This operation was repeated .«o often that there could be no question as to the eff(>ct it produced. From the foregoing experiments, I hnd that the following con- ditions are iieee. roccivina; plato must })(• soft and ]>lial)k', uiul iimst lie a ('(inductor of t'lcctncity up to the ])oint of contact, and there c a I'ubbini!' or jiiidinu' cuntact. •ith. The paiMs in c preserve tlic nccfssai'v dcuTce of I'csistance. It will he seen that we luivo hoi'O the conditions of a static charLa', the jilate receiving one polarity from the battery, and the hand tlie other jiolaritv : the interjiosed resistance ]ireveritiiig in u u'reut deurec the dvnaniic eircct. Jt is a well known I'uct. that Jug. VI. two bodies statically charged with opposite clcctricitios. attract each other. May not this be the vfhole solution of the ]ihcno- menon, that each wave as it arrives at the receiving end becomes 'for a moment static, which results in a momentary attraction be- tween the ])late and the ilnger, and this inunediately ceasing when the wave is gone, releases the finger with a noise or sound ? If, then, sounds are repeated asfa.st as the .sending i-ecd. vibrates, tlic production of a musical tone must follow, accord- ing to well known laws of acoustics, providing the waves are sent to line in musical order. In the winter of 1873-4, I experimented very elaborately, and worked out many new .applications of thejn'incijtle, not only to the transmissiou of muaic, but to the transmission of telegraphic GKAYrt TELEPHONIC RESEARCHES. 159 If, iustead of ilm revolviiifi: plato nnd llio animal tissno, wc place in tb(^ cii'cuit an eloctr()-iiKi<^iH't. or a mimlu'i' of thorn, and liavc a lunc playcil at the traiisuiittiiiti; end, tlio tunc will bo lioard from all these oloctro-iiiai^iiots. Tlio iimsic jiroduood will 1)0 ioiid or low; 1st, as the buttorv used is strong or weak: 2 I, as the lino oilers more or less resistance ; and 8d. as the magnets are mounted moi'c! or less fa\oi'alily for acoustic od'eots. In this ease, as in that of the animal tissue, each imiiulsc pro- duetts a sound; but it is jn'oduced diU'ereiitly in the two. It i.s u well known fact that an ii'on rod elongates wIuml magnetized, and eonti'acts a^iain when dcma'/ni'ti/od. TIk; elongation and contraction are so sudilon, that an audible sound is ])roduced at each change. In order to convert this sound into a musical tone, o is only neeessary to repeat it uniformly and at a definite rate of speed, which shall not be less than sixteen nor mor(> than four thousand per second. When the electro-magnet is properly mount(>d the tone may bo mari- mouts was the fact that not only simple, but composite toucs 160 TIIK .SI'K.VKI.VO TKLEPHONE. could be sont tlinmpli iho wire and received, either on tlie metnl plate or on tlic uia.u'nct. Sot only I'ould a simple melody be transmitted, Imt a harmony i>v (hscord could lie ennally well. From that time 1 have workccl assiduously with the view of makinLT a ra[Hd t('l(',L;'ra|ihic system cmliodyin.L^' this discoviay. The lii'st step was to iiiialyzc tlu' tones at the ri'ceiving end, wliieh, if suceessfully aeeomplished, would open the way to a multiple Morse, u last printing, an iiutographie and other sys- tems. It woidd bo impossible to give in this paper all the experi- ments tried, for they were very many indeed. 1 accomplished the analysis in a number of way.^. The method which seemed in all respects to give the be.st satisfaction is as follows: Fig. 73 is a [lerspective of one form of a receiving instrii- I Fig. 74. inent called an analyzer. The construction of the instrument is very simple. It consi.sts of an electro-magnet atlapted to the resistance of the circuit where it is int(>nded to be used, and of a steel rihbou .strung in front of this magnet in a solid metal frame, and jirovided with a tuning .sci'cw at one end, so aa to readily give it the proper tension. The length and .size of tlii' rihhon depends upon the note we wi.sh to receive upon it. If it is a high note we make it thinner and shorter ; if a low note we make it thicker and longer. If this ribbon is tuned so tliat it will give a certain note when made to vibrate nu'chanically, and the note which corresponds to its fundamental is then transmitted through its magnet, it will respond and vibrate in unison witli its ti'ans- mitted Xiotc ; but if another note be scut wliieh varies at all Ii'om GRAYS TELKI'ilOXIC KESKAKCllES. 161 its fiinflamonttal. it will not rospond. U a oompositc tone is sent, the ril)b()ii will rpspond when its own note is Ih'iul^ scut as a part of the composite tone, Imt as soon as its own tf^ne is left out it will immediately stop. Tims I am al)le to select out and indicate when any note is bcinu- sent, in lad, to analyse the tones which are j)assin,L( over the line. This method of analyzin,u' tones transmitted throuLdi a wire electrically is analugous to ili'lmlioltz's method of .•^(>)>arating tones transmitted through the air. The transmitting instruments n.scd in sending composites tones, are made similar in e\cry rcs})ect to the one slunvn in lig. 70, A' -1 t- LINE CARTf-l except that each reed is separately mounted. A cut of one of these transmitters, used in tclcgi'aph work, is shown in fig. 74. P'ig. 75 shows a diagram view of two transmitters and two receivers, with their connections. T^he local circuits, with their magnets, are left olT to avoid confusion. A and ]3 rei)rcsent two transmitters, placed at one end of a line. A' and IV, two receivers at the other cml. One end of the main battery is connectcil to line, and the other end to ground. Each transmitter is placed in a slnint wire, running from its main battery cunnectiuus around ouc half of the battcrv, A 162 TIIK SrKAKINi; TKLKI'lIONK. t'tiiiunon open circnit koy is ])1;u;l'(1 in cacli of those; slnnit wires. >5U[i|)t;n:ilv on the line. If the key of transniitver A is closeil, lialf of till! iiatteiy is being thi'own on and o(T ihe line, at the rate of 26-1- times ])er second, 'i'liis causes a succession of electrical wave- to How tlirongh the line at tlie same rate. If now the steel i iiou of the analy/er .V has lieen tuned in unison with these electrical waves, it will respond and hum the same note as the transmitter; but, if it is not in unison, it will remain practically quiescent, so that the n(;te can only be heard \>y sub- mittinL'' it to the most delicate test. To bring it in unison it is Fij. 76. only necessary to turn the tuning screw np or down, as the case may be. When the fuuduracntal of the ribhon corresponds with that of the sending reed, it .innoun(n>s the fact by sounding out loud and full. If (having the l<(y of transmitter A still closed, and consec[uently its corresponding analyzer still sounding) we clo.sc the key belonging to transmitter B, the other half of the battery will be thrown on and olT the line, at the rate of 320 times per second, and. another succession of electrical waves will How through the line, this one l)eingat the rate of 320 times per second. If the analyzer B' i.s in projter tune, so that its fun- damental is the same as that of its corresponding transmitter B, it will hum its note as long as the kev is closed, making a chord GUAYS TKI.KPllDMC KKSEAUCUKS. 163 witli A'. Ill tho sivmc way. a j/rriit iiumlM'r cif (lilTcrcnt )K>t03 may be somidiiiL'' at tlii; same tiiiif. at oinj t'lul nf ;i t('legra[ilii<; liiii', ami Ix; licai'il siiimltaru'Diisly at tlu^ otlicf rml. each uuto WDimdiii^' upon ;i iliHercnt rccciviim' iiistr-uuiciit. Tliu maniHT of makiiiL'' tli'-si' vil>rati()iis of lln- analyzer operate a suiuuler, a register, or other reoonliiig iiistruiueut, is shown ill fii' 76. 'I'he light eoiitaet lever <• is ami' 1 with a contact point at its free end, resting merely by the weigiit of tho lever itself in tho coneuve eiip (/, upon the, extremity of tlie armature a. When the armature is ihi'owii inio \ ihratioii tho contact le\'er ho[is ii[) and down, and docs not close tho local circuit (whicli is connected to / and Zj) witii siiliicii i.' linniiess to actuato the sounder, but when tho vibration stops tiio local circuit is closed. This I'overscs llic writing upon the si lundii', but it may bo op(>r- ateil by means of a local relay, or arrangcil in \;irious other ways which readily suggest themselves. 'I'Im' cmiplcto o[ieration is as follows: WIkmi tli(! o[)erat()r, at tlie sending statii^ii, closes liis key, l]i(i armature n, !> d is thrown into vibi'aihui, and remains so a.s long as the key eontinucs closed, but comes to rest imme- diately when the k(>y is opeiietl. I'Ik; lever c, not being able to follow the armature, rattles against it with a buzzing sound, dis- turbing the continuity of the, local circuit by throwing in a great resistance at the point (/. 'I'his resistance is sullicient to act upon tho sounder the same, jiractically, as a dead bi-eak. By tins means the sound r is made to follow tlio key of the; operator who is sending the propei- iiDte. In llie same manner ail the other tones may lie brought into service, each igiujring the other, and each seeking its own at the receiving end. A simpler eonstruetion i>f tho analyzer, and tMio which r(>n- ders the .sounder unneees.siry, is shown in lig. 77. The elee- tro-magnet M M, whicli has very short cores, is ]iroviiled with an arinaturo a, rigidly attached to the lower core, but scjiaratcd from the upper one l)j a space of ^'^ of an inch. M'his maybe increased or diminished hy'moviug the upper core in or out, by means of the screw 8. Tho armature is made thinner at the 164 TIIK SI'KAKIMI IKI.KrilONl ]K)int 7>, l)cing filnl ilowii until it; vibnitts to !i cortain nolo, llic riicci- iidjustinciit; licing ud'omplishcfl l)y adjusting the inov;il)k' weiglit W. 'I'lic wliolu is mounted upon ii sounding l)o.\ B, open nt one nid. wliicli is termed ;i resonator. 'I'lic prineij lis involved in tlio action oftlie resonator is this : A volume of air eontained in auopeu vessel, when thrown into vibrations, tends to yield a certain note, and eonseipiently strei.gLliO'.s lliat note, when the latter is sonnded in its neigliborhood. By placing the instru- ments upon eorn'sjiondiiig rcsonator.s. the sound is greatly strengthened, so that an operator may readily read iiy sound Fig. 77. the tele,gTaplii(^ charaetcns into which the continuous tone is broken hy the transmitting hey. Bv tiiis method not onlv mav diJTeront.me.ssages Im scntsimul- taneously, hut a tune with all its parts may be .sent through hundreds of miles of wire, and be ilistinetly audible at the receiving end. 1 Gray's electro-harmonic telegraph is founded upon the prin- ciple that an electro-magn(^t elongates under the action of tlie cleeti'ie current, and contracts agaiiL when the eui'rcnt ceases. * Ainor'u'aii Mocliiinical D'n'tinnarv. Vol. iii. (Tlio iiivciiliDii licru closurilnil is tt •iiodificatii)ii ot tUiit slinwii uii liarjcs l.j'.i ami \i\').) OKAYS EliECTKn-IIAHMONIC TELKl'HONK. 165 (-.'oiisequcntly, u succossion of impnlsos or iiitcrrupliouH will caiisii tlio iiiiigiict to vil)ruto, iiiul if tlicso vil)i-iitioiis ho of .siifR- ciciit frequency, a musical tone will \k' pi'iMlurcd, tln^ [litcli of which will depend upon the rapidity of the vii)rations. By interrupting an electric current at the transmitting end of a line, with suflicicnt freipicncy to produce a musical tone by .ui instrument vibrated by said interruptions, and transmitting the impulses thus induced to an elcctro-mnguct, at the receiving end of the line, tlie latter will vibrate synchronously with the trans- mitting instrument, and thus pnxUiee a musical tone or note of a corresponding pitch. Fi'j. 78. The instrument shown in tig. 78 consists of tlie transmitting a])])aratus, mounted on a base b(i:ii'd, and a receiving apparatus, shown in a position l)cncath the former. The induction cuil i' has the usual ]>rimarv and .secondary circuits. An onlinary automatic clccti'otomc c has a circuit-clcising S[)ring c'l, so adjusted as, when in action, to produce a given musical tone. A connnon telegra[ih key d is ]>Iaccd in the primary circuit a a, to nudcc or break the l)attcry connection. The key l)eing depressed, and the clectrotomc C()iisc(picntlv vibrated, the inter- ruptions of the current will simultaneously produce in the .sec- 166 THE SPEAKING TELEPHONE. ondarv circuit h b, of the i 'duction-coil, u scries of iridnccd curi'ents or iin])ulsc.s corresponding in nunil)cr with th(3 vibra- tioiKs oC tlic clccti'otonie, and as tlic receiving electro-magnet e is connected with tliis circuit, it will "he caused to vibrate by suc- cessive elongations and ''ontractions, thus ])roduciug a lone of corresjjouding ])itcli. the sound of which niav be intensihed l)y the tise of a hollow cylinder s, of metal, placed on the jiolcs of the magnet Wlien a single electrotomc c is thrown into action, its corre- sponding tone will be repi'oduc'ed on the sounder by the magnet. When ekrtrotomes c <-i, of dilfenMit pitch, arc succ 'ssivcly ope- rated by their respective keys dd^, their tones will V)e corre- spondingly re])roduced by the receiver ; and when two or more electrotom(>s an; simultaneously .sounded, tlic tone of etich will still be reproduced without confusion on the sounder, so that, by these means, mclodi(\s or tunes may be transmitted. Anotlier system is founded upon th(>. alternate making and breaking of a telegraphic circuit by means of the vibration of tuning forks, or musical reeds, as in llelmholt/.'s apparatus for the production and transmi.ssion of vocal sounds. If a given fork ])C nutde to interrupt an electric circuit by its vibrations, ami the intermit- tent current thus procbu'cd be yiassed through a scries of electro- magnets, each in coimection with a fork of dill'erent pitcii, and consequently dilferent rate of vibration, only that fork will be thrown into vibration which is in unison with the first one. Practically, the time required to do this is a small fraction of a second. The advantages of this method are mnnerous. Xot only may many receiving instnuncnts at one station be operated, each l)y its own key, through a single win^ but many dilferent stations in the same circuit may be o[)crate(l, that one alone receiving the mes.sage which has an instrument with the requisite pitch, so as to vilirate in syiK^hi'onism. .Many signals nia\', in this way, be transmitted over the .same wire at the .same time, and many dispatches .sent simultaneously to as many .stations. ^Ml this may be done, too, without affecting the line for its ordinarv use. GUAVS ELECTRO-HARMONIC TELEPHONE. 167 COMLINATIOX OF 'I'llK TELEPHONE AND MOUSE APPARATUS.' The metli(j(l of (■.•'iibiuiug the telephonic, or eU^ctro-liannoiiie, with the ordiiiiirv Morse pvstem of telegraphy, invented by Mr. Eli.sha Gi'av, o{ Chicagi), has for its objecit a moans whereby two coiinnuiiieations may be simultaneously transmitted in the same direction, or in ojipositc directions, or, in other words, to doulde the capacity of a Morse circuit, having thereon several inter- mediate stations, so arranged that while a communication is being transmitted from one terminal station to the other by means of the telephonic system, cither terminal station or any way station, may at the same time rc.'Ceive a message fmrn oi' transmit one to I'ither of the terminal, or any one of the way olliees by means of the ordinary Morse apparatus. This inven- tion has been subjected to a series of tests upon the lines of the Western Ilnicm Telegraph Company, with considerable success. One of the several circuits ujion which the system was testeil experimentally extends from Chicago to Duliu(pic — a distance of iS-J: miles — -with seventeen intermeiliate stations in the cir- cuit, the tot;d conductivity resistance of which, including all of the relays on the line, being about 5,000 ohms. The principle and mode of operation of this invention is shown in fig. 79, -which represents the instruments, in connection with th(> lini', at a terminal station, including l)oth the telephonic, or electro-harmonic, and the ordinary Morse apparatus, the former C(msisting of transmitter T, key K, local batteries c, e^ anil e^, vibrator (jr reed V^ receiving instrument or analyzer A, rejicat- ing relay A 1, sounder S, rheostat 11' and main battery B ; and the latter consisting of relay l>. sounder S', kt'v K', rneostat R and condeiiser C, the earth terminal of the line being at (i. Kacli intermedi;ite olVice is enjiip))ed with the Mor.se api)aratus only, including the condenser and rheostat last mentioned: while at the distant terminal station both the telephonic, or eli'ctro- ' Alistrih't cil'iiii iirtii'li' I'npiii tlir .Iimriiul hCiIh' Aiinrii'MM Kli'i'tr'n'ul Souic^ty, Vul. I.. No. :;, tiititlc'il, .V N'ew mill Pnn'tioal Applii'iitinu i>i'ihr Tolci>lioue, by Elisliu (iniv, Si'. J). lt)8 THE Sl'EAKlNO TELEI'IIONK. liiirmositii>n the rheostat!?, is cut out of the circuit, while that of key K and transniiltcr T is()}>eu. Disregarding for the ]ireHent the a]i})ar- r.tus at the distant t ernunal 1111 several intermediate stations, th n route of the circuit may he traced from tlie earth plate G to mai battery 15, hy wires 1 and -, to the receiving instrument or ana- lyzer A ; thence hy wire o to rheostat 11', and wire 4 to the lever « and spriiiir s of transmitter 'i" ; tlieuco hv^ wire 6 to relay 1> lay and key K^ to i\w line. With key Kclo, vihrator orieratuin ol ti'ansmitter ijiei' ^r, \] le I'oute I .f tl as or foil ows : l''rom earth pla te ( i 1 i\- wires and reed V, and wire "^ to stop o and spring s of transmitter llieiicr by station, !is wire 5 to .clay 1> and ke\' 1)1 'f( ire. ,- Ri to the line ami di.-tant 'he amount of resistance etni' loved in the rlieo.-tat K^ in ad- dition to tliatof the analyzer A, should he e([ual to the aiiparent resistance causei I hv the vilirat ion o f tl le reei I V that no variation in the streiiLi'th of llie cMirreiit goingto th(> line is mani- fested in till! Mors to a ield to the force if its retraetili nriug, thus opening th IOC al circuit of sounder S^. lie eo' nd( C eiiser U is arranger Wll h oiK! set of its poles con Ucclt to wire .) am 1 the other to tiie front .f ;e\- Ki s o as to shunt the iclav 1* and rheostat K, and thu~, when the kev is 170 THE SPEAKING TELEl'IIONE. opened and tlui ivsistanco E introduced into the circuit, the fnll diminution of the ciuTont docs not take jilace instantaneously, but only after an excecdiuglj brief interval of tiiue and in a gradual manner ^vhile the condenser is charging. Jiy this means the effect of a sudden change in the curnMit on the receiving in- stnunent or analy>^er A, whiih would tend to make the latter give a false signal, is entirely avoided. The conden.-^cr C also assists in maintaining a uniform condi- tion of magnetism in the cores of the Mor.' men- tione(l being givi'U upon sounder S dui'ing the o|)er; >n of l lever J>. Thus it will III! uiider.^tood that by a depression of key iv and the coiiseipicnt operation of transmitter n\ tlic electrical paLsi- tion3 cau.sed by tiie vibrating reed V will ]iass to the line find operate the analyzer A and reed E at the distant terminal, so as to record the culiaritics seem to l)e closclv coniK'ctcd with the short duration and llic rapid suc- cession of liu! single imjiulses. It is iiiv purixK-" in this j)aper to give the icsnits of some e.\p(>rimeuts on this subject, without :iUenipting to ])resent any wcll-(h!fined theoi'v in regard to the molecular aeliou wliicli takes place under the conditions dcscrilicd, l)Ut leaving tlie reader to make such explanation as may l)e suggeste(l In' tlie facts preseiUed. Among the I'emarkabli' developnients atteniling the intro- <]uction of the telephone there is, jierhaps, noin' more striking than tlie effect upon the amplitude of tiie recei\-ed vil)rati()ns whicii follows a change in the magn(!tic condition of the recei\-iiig elect r\perinients in the matter niiltiug nuisical and other sounds. 1 I'learly what I mean, [will at that time, were very much amazed at this new exhibition of the nnisical jiowers of their instrument.'- and I am told that one gentleman. si.\t\- mil(>s fi'om Milwaukee, closed his (jflicr that night much earlier than he was acciistonicil tf) do. Til.' relation of the insirument to the variou> i ircuits is shown in the diagram. Ilg. cSO. K ami ' represent the l)attei\ of two hundr(>(l cells used to siipjily the three telegraph lines I,, ex- tending through Wiseoii.-ni. T is a musical transmitter jilae^Ml in the short wire I'unning tn tlu! Newhall Ifuilse, and attac|i(vl to the l)atterv. iweutv cells from the irround end. I\ is a Moi'se Ivcv : ]\r is the electro-magnet, and U tlie armature "f the ido- ]ihonie rec'civer at tin- Newhall House. Tt- will be ?'eadilv observed, that ouch time the trauBmitling vibrator closed, the ri'XTLlAUrriES ok VIUKATOHY Cl'llItKXr; 173 t\V(Mitv rolls of buttory they wonlil ho sliort rireuitoil llirougli tlio I'crcivci'iii tin' Nevvliail llousi; uiid ;j:rnuii(l, thereby proportion- iilelv (liiiiiiiisliiii" tlic i)(»\vcr«>r the whole batterv and restoriii"- il again each time thi' vibrator opened the short circuit, thus sendiiiLT a series i>[ vibrations su[)er])(>-;ed npon the uuifi)rni ciii'- rcnt llowing from the lar;!-er iiatteiy throughout the lines su|)- jilied by it. 1 was well ;i\vare that twenty cells of this form of battei'v, connected 1o tla- three lines as shown, would not jiroibK.-e sueli marked ell'ect upon so many magnets and at so great a ilis- tuneo ; and 1 was naturally led to conclude that tlio one hundred oi' more c(,'lls of the additional batterv. which were not thrown 3^ K -.1^ P JT T Oil [£j Fig. 80. into aetion by the transmitter, in sattery. divided into four sections, upon each (^nd of this wire, as shown in mv patent for a multiple circuit, tiled in the United States Patent Oflicc, January 27. 1S76, in whicli it will 174 THK SPKAKiNC TKl.KI'IIONK. II" be observed lliat the batteries arc eonnectcd to tlie 1\vo ends of the lino in the usual way for an American Morse circuit. The two l)atteries were divided into four sections by shunt wires, in each of whicli was inserted a transmitter or a vibrator and a Moi'sc key, wliich stood o]icii cxcc[it when uscl [\'y trans- mitting^ signals while the vibrators were in oiK'raliou. If the key belonging to any viljrator was depressed, it woidd throw in vibration iho section of battery included in its short or shunt circuit. l)y tl:is arrangement I had as many as eight I't'ccivei-s in operatiim simultaneou.sly, each receiving a tone dill'ci'ing in pitch from the others, and eacii having a vibration strength of twenty-iive cells. One CN'cniiig I wislird to uKdv(^ an c.vpeiMmcnt with one tone Alp'^ll K X im Fhj. 81. only, and for tliat purpose inserted only twenty-live; ci'lls in the circuit, leaving out, the other one hmi(lr''d and scvcuty-rive, as it did not occur 1o lui; at lirst that the battery c(>lls It'l't out would play any p;ii1. in a vibration not, included in the shunt wires behiiiging to their partictdar tones. ,\s Iweuty-live cells were all ihat were used in transmitting any out; single tone, [ sup[)osed that amount of battery Avoidd be suilicient for tin; experiment that I wished to try. Tlic position of the l)attery and instru- ment in relation to each other is shown in lig. 81. ¥t is a battery of twenty-live cells. 'Y is tlu; vihrator and K the key inserted in a sliort or shunt circuit thrown around the tweiUy-live cells of Ijattery. ]\r R is the telephonic receiver. 1 was sin-priscd at first to find that no perceptible effect covdd be felt ou the receiver I'SE OK Sfl'l'I.JvMKNTAI- JIA'ITKUIKS. .(O ilion tlin key -wan clijsed and tlw batterv tlirown into v ti()ii. Ai'tcr workinj; over it I'lH' sumo time, mcli liil';l- i(l(>i| thill tlicM'C must ])0 some fault in thr connections, ami iii-ocefilcd i( test tl 10 wires 1)V insci'tiii'f a Morse relav I li luiid tlu; cnvMit all I'i.yht, when a recollection of my fnrmer cxiicrieni'c can>cd nie to jilace in tin.' circuit, an iidditional liattcry i)f one hundred cells, leaving; the \ilii'at<)i' and shnnt wires a> tl ie\' Wel'O helnre arouni 1 tlie twcnt\'di\'G cells oiilv. ^I'iie ari'anL;enii'nt after tin nlihtioiial one hun drcd ceils were insertc^l diown in li,L!'. S2. M 11 is the reecivinjf telephone, 'V the lele])lionie transniittei'. K tlic Morse key. e twentvdive cells. ]'] represents one hundred cells of battery, and Wl len the key was now closed, the receiver respondc d without Ms -H- [£] F,]i. S2. dilRcnlty. By inserting an additional ;nnount, of liattcry in the circuit at the recei\ing end, the aniplituile of \-iliratiou on the receiving reed, wdiich was tiinc(l in unison with \\\o, transniitti.'i', was still greater. I lia\(! vei'ihed this cNperiment at dilfereuL times sincti the alinxe ilate, and on ddTerent lines, \arying in length up to ii\(; huiidi'cd miles and oxer. It will 1)(! oliser\-ed liy studying the diagram in fig. 82, that the only etl'ect the vibrator could have u[)ou the circuit, when the key was closed, was to throw into vilir.aiou the twenty-five cells included in its short circuit, ataratecorrcspondingto the fundamental of the vibrator. It would seem that no cll'ect could be had from the one liundrod or more additional cells, inasmuch as they were simply inserted in that portion of the circuit which was never broken or opened. 176 TIIK Sl'KAKINd TKI.KI'llONK. [ill ox('0]it to prodnco !i porniiinoiit mngiiotic offoot in tlio rooeivin.L'- iiiii^nn't corresiioixling to its iMinviit strength. In otlicr wofds, if till" mairiiL'tic cllVct jirodiwcd l)y tlu; one hiiii(ln'(l cells is vcjut- sriitcil liv twc'iil V. tWrlif. -Ii\i' ddiliiiiKil cflls wiiiild iiicfi iISC till iniigiictio otlVct to ii L'ortiiiii iioint aluivf Isventv, a lid when lal en .fl it won! to twcntv, but not be! ( p\v. Is is rcprcsi ntcd hv ii Vf ir the power of tli(5 twcnty-livi" wliy slioiild it not be exerted with ei|iial |iower widioiit the one linndri'il cells inserted in tlio ciiTiiil, as described? This was the probl(Mn, and. in ;i, ineasnre it is a prolileni still, although I have satisfied myself in regard to certain fai-ts wliicli help to sti'i'nL''tlien the theorv which 1. then lu'ld in roLi'ai'd to the matter. I ■il at that ti - ^^ i eonld aceount hir at least part ol this i^fleet, upon tla^ theory that the speed of the signal was increased by tlie additional jjotential given by the larger nnnilicr of ceil.s. Tu other words, the vidno of any given <'ell, or number of cells, when fornung ])art of n lai'ge battery, is greater, especially if used on long lines, than when used alone, 'i'his theoi'V, how- ever, is entirely inadcipnite to account for the whole efTcct, us will apjH'ar fi-oni what follows. Some very inti'resting experiincuits bearing npon tiiis matter were made by mc while experimenting with the s|)eaking lele- jihone, known as the battery or snpplemental-nuignet ti'lephone, a diagram of which i.s .shown in fig. 83. In this instrument no permanent steel magnet is used : nor is there eonnected with it a battery eurrent llowing through the main line. Insteail of a ])ermanent steel magnet, sueli as is more commonly used in S[)eakingtelei)hoi\es, I nsed an eleeti'o-magnet. B. which is held [lermanently ehargeil by a local battery. The electro-magnet C, •which is ne.xt to the; diaphragm, and wdiich conne-'ts with the line and ground, and a corresponding magnet at the other end of the line, are charged by induction from the core of the magnet B, which, as before mentioned, is charged from the local battery. Before a battery current had been ])assed through the coils. and while the cores were perfectly neutral, I madi; the following MAdNKTIC CORKS KOU 'I'ELKl'IIONKH. 177 experiuieul : I coiiiuH'ted llw tclcpbDiics to llu; two fiuJs of tlie lino, !LS sliowii ill li^^'S;{, ami put on ii, looul Imttcry at station No. 1, si lowii at the I'iLjlit hand df lli with iiia'nict B tin tl niu''h the wires ha'_'ruiii. fdiiiH'ctiiiL'' thi' 4 k Thr iltciy local liattciy iit sta- I'ur lh(! tiiiK! left lion No. 2, at the left of the diaLfraiii, was iiiiconnt'cted, so that the core of the inaLniot B, and also that of were both in a neutral state. I now iilai/ed iii\' ear to tl telejihone at slutiou No. aiK I ha.l my assistant speak in a loud tone into the instrument at stition No. 1, win ch liad the local battery attached, and was therefore in condition to transmit tli electrical vibrations produ I bv the motions of the diaphra; isni 1 i Cl B H 1 n ic m p H^iH La Fiy. s:i. acting inductively upon the then inaiinctized electro-magnet C. Although the vilirations were, passing through the circuit, and consequently through the coils of magnet ( '. at station 2, I could get no audilile eflfect until I jmt on tlu^ local batters' and charged the cores of tliC magnet at the receiving end of the line. Im- mediately after this was done I could hear every word loudly and distinctly, making in all respects the best telephone I have; ever heard, due to the fact that by tlu; aid of local batteries we. I an make of soft iron a much stronger magnet than can be made of steel. 1 then threw ofT the battery at station 2. when I could hear the won Is very faintly, and I w;is able then to transmit \-ery faint sounds, due wholly to the residual charge left in the iron after the batterv was taken olT. It is I'asv to see whv no sound. IMAGE EVALUATION TEST TARGET (MT-S) 4 / {/ u -% o > ,V4 MA 1.0 Ui%2S 12.5 1^ 1^ 12.2 1- lllll^^ U 1.4 |,.6 I.I 1.25 ^ 6" ► V] <^ /2 v: OMy ^ # "^ vV V ^. Photograpmc Sdences Corporation 23 W2ST MAIN STRHT WEBSTER, N.Y. H580 (716) 872-4503 ^v k\ iV 178 THE SPEAKING TELEPHONE. (•ould bo transmitted from tho apparaturf before it had been charged by the battery, because there was neitlier electricity nor magnetism present, nor had we any of the conditions n(^(;essary to produce either of tliese jorees by sim})ly speaking against the diaphragm. This was not true, liowever, of tlie No. 1 station, because the battery was connected and tlie magnet charged. No (h)ubt tlierc was some effect produced upcm tlic receiving magnet, for tlie electrical imjmlses passing through the line must have been the same wlictiier the magnets at the receiving end were charged or in ii neutral condition. Tliis one fact, however, was prominently brought out, that in order to make an electro-magnet, which is tlie receiver of rapid vibrations (such as will copy all the motions made in the air wlien an articulate word is uttered), sensitive to ;ill the chang(\s necessary in receiving sounds of varying (piality, it must bo constantly charged by .some foreii exterior to tlie electrical vibrations sent through tho wire from tiic transmitting station. AVc were well aware that tliis condition is unnecessary where tho force transmitted is of suflicient magni- tude, or where the signals are of .sufliciently long duratioa My experiments k>ad me to tlie conclusion that a .soft iron core is far more susceptible to the slight changes in the electrical conditions of the wire surrounding it when it is already in a high .^tate of magnetic, tension. It is like an individual who, in his more calm and unrudled moments, may be surrounded by little waves of excitement without being ail'eeted by them ; when on the other hand, if from any cause whatever, his nervous sy.stem is in a state of tension, he is readily ailected liy every di.sturbing influence, however slight. It will b(Mii)ticed that the above observations were made in regard to I'lectrical impulses of very short duration ; the longest several humlrcd jier second, and tiie shortest many thousand. The explanation of the aliove results may be j)artly umlerstood when we fully consider tlu^ elTects of the extra current which is induced in the ])riniary circuit itself; (^specially when such cir cuit has included in it the coils of an electro-magnet. The lirst effect from a current of electricity iiassing around HEACTIVK EFFKCT OF INDUCED CURRENTS. 179 tln^ coils of an olectro-mafniot is to ut as soon as the coro begins to magnetize, it M'ts up a nioMHMitarv induced current in tlie ()])posito direction to the ])riniary or inducing current, thsiblo explanation of this phenomenon may be found on the supiiosition that, when the molecules of the iron are in a state of magnetic tension, that is to say. when they hnvi' moved from a neutral jioiiit up to ;i given position, there is then K'ss molecular inertia to overeoine in mov- ing them forward. The ])riiiciple here suggested finds an analogy in the superior resonating (pialities of a sounding-board wliicli is under mechauical tension, as compared with one in a neutral stat(>. It follows from the obscrvaticins mach) above, in regard to the resistance to the jiassagc of rapid vilirations through a helix having inserted in it an iron core, that any electro-magnet in- serted in the circuit through which rapid \ibrations are electri- cally transmitted, will eitliertotally absorb tlu'in orgreatly dimin- ish their power. T!:is is found to be true in practice, and it was Ji serious probliMii how to successfully use Sj.^.iking telephones u})on lines where mon^ than two stations were necessary. In 180 THK SrKAKING TELEPHONE. order to be able to call the party with whom we wish to comirm nicate, it is iiocossary to have bell inagncis, or other signaling a|j|jaratiis involving the use of an electro-magnet, and tliese magnets must be in circuit when tiie line is not in use, to be in position to receive a call from any station on the line. If A, B and C, have offices on the same line, and A should signal to C, they would both switch out their bell magnets and switch in their telephones ; but B's bell magnet would still remain in cir- cuit and act as a resistance to the i)assagc of vibrations over the line. This difhculty is fully obviated by the; use of a (condenser, which is phuted in a branch circuit })assing around the bell mag- nets. So elTectual is the remedy, that even five or six magnets may be inserted in the line without ])eree])til)ly diminishing the loudness of the tones over that of u clear wirc^ of the same length. The action of tlu; condenser in this case h.'is been to some extent ex])laiii<'il in an article ])ublished in the second num- ber of this journal. ' The effect of a condenser on impulses of short duration is just the reverse of that of an electro-magnet ; the latter oflering a momentary opposition to the passage of the impulse Dy creating a counter one, which to a great extent neutralizes it, while the former offers an easy jias.'^age to it .so long as the condenser is filling, which occupies a very short .space of time. The de- crease in resistance effected by the use of the condenser is only momentary, and will be of no service whatever in prol(mgcd signals. On the other hand, tlu^ increase of I'csiivtimce cau.sed by the insertion of an elec'ro-magnct in circuit is also momentary, and does not act as a retarding influence, where tlic signal or im- pulse is sufficiently prolonged, more than the same amount of any artificial resistance. I will mention another ])eculiarity which relates to the con- struction of the speaking tele{)hone, with reference to its ability to a(!curately reproduce the characteristics of any voice or any sound that may be transmitted through it or received by it i For u degcriptloii of tho applicat'iua of thu ooiidciiitcr, hco pugus 80 and 31. PR( T)IiCTION OF VOWEIi SOUNDS. 181 It is a well known principle in acoustics that that clement of sound which we call quality or chanicter is detenuined by the number of over-tones that accompany any given fundamental, and the position that tlicy sustain wiih reference to the funda- mentiil. For instance, a pure tone is made by a given number of vibrations per second, its vibratory j)eriods occur at equal intervals, and it has no otlior tones accompanying it, of any pitch or intensity whatever. As a matter of fact, however, nearly all tones are composite in their character, and the nature of their composition, witli reference to number and intensity, determines the character of the composite tone as a whole. An api)roximatcly pure tone is obtained from a tuning fork constructed with great care, mounted U])on a box whose cavity corresj)onds accurately to the pitch of the fork when the air column contained witliin it is thrown into vibration. Wl>en the fork is thrown into vibration, the sound of the vowel U will pro- ceed from tlie cavity of the box. Hence, the characteristic of the vowel U is purity of tone, and may be likened to one of tlie positive colors, unshaded by the admixture of any other. On the other hand, if we add to this pure tone, or the vowel U, a tone whose vibrations are doiil)]e the rate and very intense; also, two more tones of feeble intensity, on(! with a rate three times as great as the fundamental or lowest tone, and the other four times, we shall have a composite r(\sultant sound whose character is that of the vowel C). And .so by varying the composition with reference to number and intensity of tones, we jiroduce in turn all of the other vowel sounds, and, ia fact, every shade and variety of audible exjjression. Every change, however slight, in any single element of a comjiosite tone, either in amplitude of vibration, rate or relation to the fundamental tone in the clang or composition, produces a clumge in the quality of the sound as a whole. From this it will be observed how important it is tliat the apparatus we use in transmitting and reproducing urtieulate s})eech shall copy with the greatest accuracy, both in the trans- mission and reproduction, all the motions made in the air by the speaker. Any attempt to reinforce the viljrations, by mounting 182 THE 8PKAKING TKLEI'HOXE. the diaphragm on resonant substances, sucli as wood, ard over hollow air cavities, serves to mutilate the words transinittcd, and destroy the i)eculiar characteristics of the sound. X few mo- ments study of the laws of acoustics will suggest reasons why tliis is BO. Every solid substance of a resonant character — striking ex- amples of which are wood and some of the metals — tends to as- sume a fundamental character wlien thrown into vibration. For instance, when we striken a bell of a given size, it gives a clang of the same character at every stroke. If !he size of the bell is changed, the character of the sound or clang will change, so that everything of a solid or massive character may be said to be able to respvmd more readily to some toncb than otlici-s. This char- acteristic increases as the body assumes the form of a vil)ratory reed or tuning fork, and it diminishes as the body is flattened into a thin shajie, and assumes the form of u diaphragm, so tliat it ceases to vibrate more readily as a whole than in its equal parts. It has then nu^re of tlie characteristics of the air with reference to its ability to take up simultimeously all forms of motion. If, then, the transmitting diaphragm of a speaking telc- jihonc is so constructed anve I A devii-u origiiiully BiiffgOHted by I'rol'oiisor A. E. Dolljeur. KKKECTS PKOnUOEl) HV IIKSOXAXT DEVICKa 188 and bolow the tliaphnigm should bo the smallest possible. On tlie other hand, if the body of the instrument is made of wood, and an air cavity of considerable size is made under the dia- phragm, or if any device is employed to reinforce the tones, the effect will be to mutilate the articulation, and change the char- acter of the transiid.ted sounds. The reiuson for this will appear very plain when we consider the importance of preserving the relations of all the simple elements which make up a composite sound of a g ■eu character. Those resonant devices will resonate or reinforce S( uj of the tones of a clang and not theothei"s, thus throwing the c mjiosition out of proportion, and consequently destroying its character. 1 In tlic following l)ages, which rehite especially to the tele- graphic transmission of musical and other sounds, it is my (U'sign to give, with as much accuracy as possible, a concise history of my own experiments and observations, as they have been made from time to time since I Ix'gan the investigation of this subject. It is not ray intention to enter into the work which h.xs been done by others; but to furnish as faithful a record as ])()ssil)lo of my own, leaving tlie world to judge who is most justly entitled to priority of invention and discovery in respect to the various things licreinaftcr set forth. At the tiniewhet> I began my investigations in connection with the above sulijcct-mattcr, I had no knowledge that any one had ])rcviously done anytliing in this fu'ld. I was, however, familiar with the general fact wliicli had been made known by Page and Ilenrv, in relation to the effect produced upon the iron core of an electro-magnet at the moment of its charge and discharge. I also hud s ime general idea of the nature of the experiments of Rciss, of Germany, which were made about the year 1861, but hail no knowledge at the time, or until more than a year after I h;id been actively engaged in telephonic rescarcli, that any one beside mvself was devoting any attention to the same subject. A glance at m^' antecedents may not l)e inappropriati; at this AlistriK't of Expenrntntal lie»earcheti, by Klislm finiy, Si'. ]). 181 THK SI'KAKINO TELEPHONE. point, inasmuch as it will help to show how I came to be led into this particuhar field of physical research. Frona my earliest recollection I was profoundly interested in all the phenomena of nature, and had an intense desire, whenever I saw any manifestation of physical force, to become acquainted with the secret of its operation. WIkmi I saw a piece of ma- chinery of any character whatsoever, I usually attempted to re- produce it Of course I was unsuccessful in most instances, owing to the fact that my facilities for constructing machines were very limited, and my exi)erience as a mechanician at that early age was meagre. However, not all of my attempts were failures ; for, I have in my mind the memory of the ojieration of many ma- chines constructed by my own hands, ranging from a saw-mill run by water power to a Morse telegraphic appai-atus. Among all the phenomena throughout the domain of physics, nothing took such hold upon my mind as that exhibited in the various effects produced by the action of electricity. I read whatever I could finil relating to this subject, with the same eagerness and interest that most boys would read Robinson Crusoe or the Arabian Nights ; and many were the scoldings — to say nothing of stronger appeals that were sometimes made — that I received in consequence of my enthusiasm in experi- mental investigations in the various branches of physics. As I look back from this jioint, however, I feel no disposition to com- plain of what I then not unnaturally regarded s^;; harsh treat- ment; for I can readily sec that it was not altogether ])leasant for my mother to find, as she sometimes did, that whole skeins of flaxen threail, which she had s))un with her own fingers, had been used u]) in manufacturing belts to d.'ive machinery which in her eyes promised very small rcsidts; or to discover that her best ease-knife had been notched into saw-teeth, with which to equip a miniature saw-mill. Neither was it altogether agreeable to her feelings to find her only quart bottle — for quart bottles in those days were rare, and highly prized by t\w housewife — converted into a cylinder for anelectrical machine ; or to have the copper bottom of her wash-boiler cut up to make the plates GKAVS EARLY EXPERIMENTS. 186 of a galvanic pile. I even think I wonlcl have invaded the sacred precincts of her l)aiidbox, which wa-s only opened once a week, if thereby I could have made its contents subserve a pui^iose in connection with any of my boyisli schemes. While yet a boy I constructed a Morse register, all the j)arte of which were made of wood, with the exception of the magnet, armature and embossing point in the end of the lover (which latter I made by filing a nail down to a point). I had the magnet bent into a U form by a blacksmith, and then wound it with brass bell-wire, which was insulated with strips of cotton cloth wrapped anjund it by hand. For a battery I made use of a candy jar, in which I placed coils of sheet copper and zinc, with a solution of blue vitriol. "With these materials I succeeded in making a very good electro-magnet, which would sustain nearly a pound weight, and which, when mounted as a part of the instru- ment, performed tlio work of actuating the armature with per- fect success. At quite an early age I was apprenticed to a blacksmith, and worked with him at that business about one year. Some of the edge tools which I made daring that time are still in my mother's possession. I soon found, however, that this business was too laborious for me, as I was naturally of a rather frail constitution. I therefore relinepiishcd it, and biicame an apprentice to a car- penter, joiner and boat-builder. I served a full apprenticeship, during which time I was employed in almost every department of wood-work. The prime motive which actuated me tlirough all these years tliat I had worked at the bench was my tliirst for knowledge. I felt sure that, with my trade as my capital, I could work my v.'ay through a course of study. In pursuance of this idea, the time having expired for which I had apprenticed myself (three years and a half), I began a regular course of study, while by working a portion of each day and during vacation at my trade, I was enabled to pay my necessary expenses and keep up with n\y class. Here, as everywhere else, the capacity and ability to master everything relating to physical .>ression upon my mind, and dcterniini'd me at once to take the matter up in earnest and see what might bi' in it. I procured a violin, and taking off the strings, sukstituted in their jilace a thin metal plate j)rovitled with a wire connection, so that I could attach it to one pole of the induction coil or bat- ( III fiij HATH-Tl" » KX I'KIUMKNT. 187 n of •h is 3d in Fig. 84. 188 THE SPEAKING TELEPHONE. tery, tliuH ])lafiii^' it in tlio aiiu' position, witli reference to ilie body, that tlic ])atli-tiil) was in the original exj)criment. By nibbing the plato in tlic same manner as before described, the sound of the electrotome was reproduced, acconipanicd by tlic peculiar quality or timbre bclongitig to the violin. 1 noticed, however, tliat the characteristics of the initial vibrations were faithfully preserved, and all that was needed was to sift out rucU foreign vibration."? as w o c.\cite«l in the receiver, owing to its peculiar construction ; i'< which case there would remain the exact cluiractc'- — nothing more nor nothing less — of the transmitted Fiij. 85. vibrations. Fig. 85 shows the violin and the manner of holding it when in operation. I subsequently .sukstitutod for the animal-tissue receiver an electro-magnet conibinccl with a hollow box of tiinied iron, hav- ing an opening in one side, whih; the oth(>r was held over th(! poles of the magnet at such a distance from it as would iiroduce the best effect. TKANSMISSION OK OOMI'OSITK TONKs. 189 With this nppiinitus I noticed tlwit when I dejircssed two keys on my tmnsmitter, it tlies(> v/viv in tlic j)ropcr rohition to cai'li otlicr, !i coniposite tone would bo received, tIniH deinonstrutiiig tlio jfeneral fact, tlmt with ii receiver properly coustnicted and a transuiitter properly niadc; and arrange ^1 telegraphically. This apparatus is shown in fig. 86. In hot'i of these cases I u.^ed an induction coil, placing the tranynii iters in the primary, while the line was connected to the secondary coil. The aliove fact respecting composite tones was more strongl v' impressed upon my mind when I completed my musical traus- -^Itittlt 'j; Fi'j. 86. mittcr, having a scries of tuned reeds corresponding to the dia- tonic scale. This instrument is sliown in iig. 87. When the fact dawned upon me, and liad l)een confirmed by demonstration, that sounds of a composite character could be transmitted through a telegraphic circuit and reproduced at the receiving end, and the possibilities of the invention and the great results to which it must eventually lead ]iassed through my mind, I at once foresaw so many possible ap])lications of it that it became a serious question which line of investigation to lirst pursue. Among other conceptions of the probabilities of the invention 190 THE SPEAKING TELEPHONE. ■was that, at an early day, not only musical compositions of a complicated character, but oven articulate speech would he trans- mitted through a single telegraph wire. In addition to this, I could plainly sec, also, how that musical tones, dillering in pitch, could bo siiuultancously transmitted throufTh the wire and analyzed at the receiving end, so that a transmitter and a I'eceiver corrt'spoudiiigly tuned would trans- mit and receive a tone corresponding to their own ])itch. reject- ing all others ; while at the same time a number of other tones Fig. 87. differing in pitch might be simultaneously transmitted and re- ceived through the same wire. In truth, the general fact had already been demonstrated, but thc'c was still needed that perfection in the details of apparatus and arrangement of circuits which' were essential to success. Another conception which c^-'uried to me at this time was that of applying the invention to a printing tel(>graph, so that each type would be actuated by a tone of a jiarticular pitch. Having all these uses in my mind, and supposing I had seciu'eil in my lirst patent the fundamental principles that would underlie all the various applications that might bo made in the VARIOUS FOKMS OF TUANSMirriNU REEDS. 191 matter of transmitting sounds telograpliically, I pursued m\- investigations in a systematic way, placing each development to tlie credit of the jiarticular application to which it seemed to belong. Being well conversant with the facts, so far as they were then known in the sciences of electricity and magnetism, I was fully prc[)arcd to avail myself of what had already been done in that line. I was not, however, experimentally conversant to the same extent with the facts in the science of acoustics, but theoretically the subject was a familiar one to me. I devoted eonsiderable time to familiarizing myself experimentally with that science, es^ 'cially that branch which related to the (pialities of composite tones ; so that I was able to give the composition of the various vowel sounds, and determine in general the relation between the character of a sound as it seemc(l to the hearer and the physical fact as it existed in the form of motion, cither in the air or any medium through which it was pi'0])agated. In this connection I madt^ a number of experiments having reference to the transmission of sounds varying in iiuality. I devoted myself principally to the construction of various de- vices for transmitting musical tones telegraphically, for this seemed to be the lirst fundamental .step to take in the direction, either of musical or of multiple telegrapliy. I accordingly experimented with various forms of transmitting reeds, one of which consisted of an ordinary electro-magnet and a reed made of a ])iece of watch-spring, one end < " Inch was fixed to one pole of the magnet, while the other or free end projected ovr the other pole, a short distance from it, so as to form an arniaturc. The circuil: which actuated this reed, after passing from one pole of the battcrv through the helix, was cotmected to the magnet cores, thereby making the reed a part of the circuit, the pole being connected to a ])oint r(\sting against the reed one third of the distance from its lixed to its free end. The transmitting reed above describesponding too readily to the harmonics of its fuudamentid. Another ilifficulty Fig. 89. . was, that the free motion of the reed was impeded by its com- ing in contiict with the break-point, where the current is inter- ru{)ted. To obviate the first objection, a reed was made of heavier material, and tuned by filing it at one point, near its li.xed end, as shown in fig. 88. To obviate the second objection — the VARIOUS FORMS OF TELEPHONIC RECEIVERS. 193 solid contact between tlie reed and })reak-point— a short and thin intermediate spring was mounted upon the reed, the free end of which came in contact with the break-point. This inter- mediate spring is shown in lig. 89. Several fortiis of receivers invented by me have been alreadv described. Another form is shown in tig. siti()M. Upon another standard, mounted on the same base and ni'ar to it, was tixed an electro-magnet whose poles projected into the ])an, and nearly, but not (piite, touching its bottom. By means of a screw between the two standards, T was enabled to secure the proper position of the magnet with reference to the Fig. 91. diaphragm. I sometimes used a sui^plemcntary brace (not shown), which rested against tlie top of the rim, as an additional means of more rigidly holding the diaphragm in jwsition. "^riiis instrument I used in connection with various transmitters, especially with tlie one shown at fig. 87, and was the -osult of a series of experiments with thin iron and steel plates mounted over the poles of an electro-magnet. This I found to be a con- venient way of mounting thin plates. It will be observed that VAKIOUS FORMS OK TELEPHONIC RECEIVERS. 195 this instrument embraces all the substantial features in the ine- clianical construction of the speaking telephone of to-day. When used in connection with my articulating transmitter, articulate words have l)ecn received ujton it, and when a duplicate of the instrument is inserted in a closed circuit, which includes a gal- vanic battery, it becomes a speaking telephone capable of acting both as a transmitter and as a receiver. I designed another method of transmitting, which I called the organ-pipe transmitter, shown in lig. 92. The drawing shows a top and a side view of an ordinary organ pipe, with a space cut away at the centre, in length about equal to Fig. 92. the width of the pipe, and in depth just the thickness of the ■wa . . the pipe, making an opening which was covered with a thin diaphragm h. A screw I), provided with a ))latinum point projccing through a mcfal brace d secured to the side of the pii>e, was adjusted very !>ear to the diaphragm h. The latter had glued to it a thin piece of platinum, to which was connected a small wire c, terminating in a binding post C. It is a peculiarity of an organ-pipe with an open end, that when its fundamental note is sounded the waves are con- densed most powerfully in a lateral direction in its centre. I took advantage of this fact to profluce a vibration in the dia- 196 THE SPKAKINO TKLKl'IIONE. phragm b, which would make contact at each movement with the screw D. As the condensations and rarefactions of the air in the tube were synchronous with the vibrations necessary to produce a tone corresponding to the fundamental of tlic pipe, it is j^lain that the movement of the diapliragm would be the same. By con- necting a battery and receiving instrument through the bind- ing posts and the point D, when the organ-^jipe is sounded its proper tone will be produced on the receiving instrument by electro-magnetic action. Fig. 93. I made a scries of these transmitters, operating them with a bellows, and when worked with uniform pressure of air, they produced splendid results. In fact, it mckcs a very good form of transmitter, and other things being equal, would be quite as good as the one we have most generally used This method of trans- mission, however, involves the employment of a bellows, pro- vided with some attachment for maintiiining a uniform pressure, as well as with power to work it; so that it seemed, at least for t(',legraj)liio purposes, that some form of transmitter having electricity for its motive power would be more appropriate. I TELEPHONIC TRANSMITTERS. 197 nth the r in the produce is plain By con- ic bind- sounded tnent by therefore continued to prosecute my experiments in that direc- tion. In order to diminish the number of magnets in a transmitter having a large number of reeds differently tuned, I designed a compound magnet, as shown at fig. 93. This consisted of two ordinary electro-magnets, with their poles far enough apart to give the proper length to the reeds. I con- nected the positive pole of each to the ends of a bar of soft iron about eighteen inches in length, and the negative pole to a similar bar, so that when the magnets were charged one bar would show m with a air, they )d form of te as good i of trans- lows, pro- 1 pressure, t least for [;r having ipriatt;. I Fig. 94. positive or north polarity and the other south. The magnetism was about equally distributeil through the length of each bar. This arrangement enabled me to get a large number of reeds upon a small number of magnets. I found, however, that the power was too much distributed to produce good results upon any single reed, without increasing the battery to an undesirable extent, so I abandoned this form and subsequently constructed the one shown in fig. 94. This is substantially the same as my transmitter shown in fig. 198 TJIK Sl'KAKINU TKLEIMIONK. 87, exoopt tliat I use two and three reeds upon eaeli magnet, all diiTcrently tuned. Another furin of transmitter invented by me is sliown in iig. 95. It consi.sted of a revolving shaft, upon which, were inomitcd two eccentric cams, having one or more jirojections. These actuated two small levers, causing them to vibrate ujton their respective break-points, through which points a battery current passed. From a ])ulley on this shaft I connected a belt to one of the wheels of a lathe which was driven by steam power, from which it deriveil a uniform motion and a dclinite rale of speed. Fig. 95. I refer to my experiments with this particular apparatus because, although simple in themselves, they were the means of giving my mind a new impulse in another direction, and one which soon conducted mo to the solution of the problem in- volved in the transmission of articulate words. I employed, in connection with this transmitter, one of my common receivers which was adapted to the reception of all varieties of sounda The pressure of the levers upon their contact-points was con- trolled by elastic springs. When this apparatus was put in operation I noticed that a 1i TRANSMISSION OF AKTICULATE SPEECH. 109 tJciiiiid of peculiar quality, not vnilike that of tlio huinan voice wlicn in great distress, j)rocuedcd from the receiver. By altering the tension of the spring in various ways with my hand, I found that I was able to imitate many different sounds, involving the vowels only. I succeeded, among other things, in producing a groan, with all its inflections in the greatest 2)erfection. By skilfully manipulating the sjjring in the manner before men- tioned, a very great] range in the quality of the sounds was pro- duced, using only a single break-point Fig. 9G. Up to the time of making this experiment I had associated in my mind, in connection with transmission of spoken words, a complicated mechanism involving a separate vibrating reed for each separate tone transmitted. This experiment jiroduced an entire change in my views, and I canio to the conclusion, that "', could alllie done l)y means of a single transmitter; although, at that time, I did not carry my experiments farther in that direc- tion, being too much absorbed in my multiple telegraph scheme. During the latter part of the spring and early part of the sum- 200 THK SPEAKINO TELEPHONE. mcr of 1875, I wm engaged in coiistnieting iiml ii(la[)tiiig my system to a type-printing telegraj)!!, au idea whirh I had con- ceived early in 1874 I had it rodiieed to practice far enough to demonstrate the applicaliility of tlio principles involved. la January or February, 1875, I constructed an operative machine, at that tiineliaving three letters of the alphabet, together with the mechanism for controlling the printing and moving the paper. An outline view of this machine is shown in ligs. 96 and 97. The model of this machine was completed and forwarded to the Patent Office in October, 1875. The y)atent on it was issued Fig. 97. July 4th, 1876, to which I refer for a complete description. The general principle of operation may be briefly stated as follows : A particular tone actuates each particular type, so that there is a transmitting vibrator and corresponding receiver for each tone. A simple touch of a key j^rints the letter at the receiving end without the necessity of waiting for a type-wheel to come into position. The printing is executed upon a sheet instead of a long strij) or ribbon, as in the ordinary step-by-step machine. It will not b{; necessaiy to describe the mechanism iii detail in this place, as it is fully .set forth in the specification of the patent itself. INVENTION OP THE SPEAKIN(} TELEPHONE. 201 During a visit to Milwaukoc I saw for the first time a toy called the lovers' telegraph, consisting of a membrane stretched over the end of a tube, and having a thread attached to the centre, the other cud of which was attached to a similar membrane. The fact that spoken words were distinctly transmitted by the longitudinal vibrations of the thread from one membrane to the ol'ijr, confirmed the idea that I liae and file it in the records of the Patent OOice. I realized that this would be a miitter of the highest importance in a .'Scientific jjoint of view; but I had no adequate conception of its value in a commercial .sense. As early as March, 1874, Dr. Samuel S. White, of Phila- delpliia, had purchased an interest in all of my tclcjihonic inven- tions that I had made or miglit thereafter make; and, as he had already advanced consideraljle money in aid of their development, I felt it iiuumbent upon me to givt; as much of my time as pos- sible to what seemed to be tlie most practical and useful feature, and the one promising the most immediate returns — that of mul- tiple telegraphy. I therefore concluded to .secure the articulating feature, and take it uj) and develop it more com])letely at another time. About the loth of January, 1876, I went to Washington, where I spent some time in a.ssisting my attorney in the prepara- tion of a number of ca^eA which had been accumulating for several months. This required several w^eeks of time. While there I put my speaking telejihone transmitter into the form of draw- ings and specifications, and, as my model was not yet ready, I determined to file the specification as a caveat Following out the suggestion made by the diaphragm and string of the lover.s' telegrai)h, I designed a transmitting apparatus ■which copied the motions of the diaphragm electrically, through the longi- tudinal vibrations of a light rod attached to the centre of the dia])}iragm. These electrical vibrations or undulations were the 202 THE SPEAKING TELEPHONE. result of the variationn in the resistance of the circuit made by the longitudinal motions of the rod, moving in a yielding sub- stiince offering a considerable resistance to the juussage of the electric current. The following is a v(!rl)atim (iopy of the speci- fication, filed in the United States Patent OlTice, February 14, 1876: gray's specification, filed kebkuary 14, 1876. To all whom it may concern : Be it known that I, Elisha Gray, of Chicago, in the County of Cook, and State of Illinois, have invented a new art of transmitting vocal sounds telegraphi- cally, of which the following is a sjjccilication : It is the object of my invention to transmit the tones of the human voice through a telcgra[)hic circuit, and reproduce them at the receiving end of the line, so that actual conversations can be carried on by persons at long distances apart I have invented and patented methods of transmitting nmsical impressions or sounds telegraphically, and my present invention is based upon a modification of the principle of said invention, which .is set forth and described in letters patent of the United Stjites, granted to me July 27th, 1875, respectively mimbered 166,095 and 166,096, and also in an application for letters patent of tlu^ United States, filc^d by me, February 23, 1875. To attain the objects of my invention, I devised an instrument capable of vibrating responsively to all the tones of tlie liuraan voice, and by which they are render 3d audible. In the accompanying drawings I have shown an apparatus embodying my improvements in the best way now known to me, but I contemplate various other applicuitions, and also changes in the details of construction of the apparatus, some of which would obviously suggest themselves to a skilful electri- cian, or a j)erson versed in the science of acoustics, on seeing this application. Fig. 1 represents a vertical central section through the trans- mitting instrument; Fig. 2, a similar section through the receiver; and Fig. 3, a diagram representing the whole apparatus. GRAY S SPECIFICATION. ao6 't r > ^ ■liW" Mr/)/CSS£S. m/rMMTQiti Mg. 98. SLU€i^ 204 THE SPEAKING TELEPHONE. My present belief is that the most effective method of pro- viding an apparatus capable of responding to the various tones of the human voice, is a tympanum, druni or diaphragm, stretched across one end of the chamber, carrying an apparatus for producing fluctuations in the potential of the electric current, and consequently varying in its power. In the drawings, the pci-son transmitting sounds is shown as talking into a box, or chamber. A, acro.ss the outer end of which is stretched a diaphragm a, of some thin substance, such as parchment or gold-beaters' skin, capable of responding to all the vibrations of the human voice, whether simple or complex. Attached to this diaphragm is a light metal rod, A', or other suitable conductor of electricity, which extends into a vessel B, made of glass or other insulating material, having its lower end closed by a plug, which may be of metal, or through which passes a conductor b, forming part of the circuit. This vessel is filled with some liquid ])ossessing high resist- ance, such, for instance, as water, so that the vibrations of the plunger or rod A', which does not quite touch the conductor b, will cause variations in resistance, and, consequently, in the potential of the current ])assing through the rod A'. Owing to this construction, the resistance varies constantly in response to the vibrations of the diaphragm, which, although irregular, not only in their amplitude, but in rapidity, arc never- theless ti'aiismitted, and can, consequently, be transmitted through a single rod, which could not be done with a positive make and break of the circuit employed, or where contac;t ])oints are used. I contemplate, howe\ or, the use of a series of diai)hragms in a common vocalizing chamber, each diaphragm carrying an inde- pendent roil, and responding to a vibration of dilTerent rapidity and intensity, in which case contact points mounted on other diaphragms may be employed. The vii)rations thus imparted are transmitted through an elec- tric circuit to the receiving station, in which circuit is included an electro-magnet of ordinary construction, acting upon a dia- phragm to which is attached a piece of soft iron, and wliich BELLS SPECIFICATION. 205 the diaphragm is stretched across a receiving vocalizing chamber c, somewhat similar to the corresponding vocalizing chamber A. The diaphragm at the receiving end of the line is tlius thrown into vibrations corresponding with those at the transmitting end, and audible sounds or words are })roduced. The obvious practical application of my improvement will be to enable persons at a distance to converse with each other through a telegraphic circuit, just as they now do in each other's presence, or through a speaking tube. I claim as my invention the art of transmitting vocal sounds or conversations telegraphically through an electric circuit. Although it is not my intention, as I said in the beginning, to raise the question of priority of invention as between myself and other parties, I will nevertheless state in this connection, that so far as I ;im aware, this is tiie lirst description on record, of an articu- liitiiig telephone wliich transmits the spoken words of the human voice telegraphically liy means of electricity. hell"s specificatiox, filed FEimrAnv 14, 1876. In order that the claims of Professor A. G. Bell to the inven- tion of the speaking tele[)hone may be contrasted with those of Mr. KlishaGray, we reproduce the specifications and drawings of the former as they were filed in the United States Patent OfHce, on the 14th February, 187(5, the same day, it will be observed, on which ^Ir. Gray filed his caveat. To all whom it itiay concern : Be it known that I, Alex- ander Graham Bell, of Salem, Massat-husetts, have invented certain new and u.sefid improvements in telegraphy, of which the following is a specification : In letters jiatcnt granted to mo April 6, 1875, No. 161,739, I have deseril)ed a method of, and apparatus for, transmitting two or more telegrapliic signals simultaneously along a single wire ])y the employment of tran.smitting instruments, each of which occasions a succession of electri'^al impulses differing in rate from the others ; and of receiving instruments, each tuned to a pitch 206 THE SPEAKING TELEPHONE. at wliicli it will be put in vibration to produce its fundamental note by one only of the transmitting instruments ; and of vibra- tory circuit-brcakei"s operating to convert the vibratory move- ment of the receiving instrument into a permanent make or break (as the case maybe) of a local circuit, in wliicli is placed a Morse sounder, register, or other tclegraj)hic a2)paratus. I have also therein described a form of autograph telegi'aph based upon the action of the above mentioned instruments. In illustration of my method of multiple telegraphy I have shown in the patent aforesaid, as one form of transmitting instru- ment, an electro-magnet having a steel s[)ring armature, which is kept in vibration Jjy tl;e action of a local battery. This arma- ture in vibrating makes and breaks the main circuit, jiroducing an intermittent current upon the line wire. I have found, how- ever, that upon this plan the limit to the number of signals that can be sent simultaneously over the same wire is very speedily reached ; for, when a nundjcr of transmitting instruments, having different rates of vibration, are simultaneously making and break- ing the same circuit, the effect ujion the main line is practically equivalent to one continuous current In a pending application for letters patent, filed in the United States Patent Olhce February 25, 1875, 1 have described two ways of producing the intermittent current — the one by actual make and break of contact, the other by alternately increasing and diminish- ing the intensity of the current without actually breaking tlie circuit The current produced by the latter method I shall term, foi- distinction sake, a pulsatory current My present invention consists ir the employment of a vibra- tory or undulatory current of electricity, in contradistinction to a merely intermittent or pulsatory current, and of a method of, and apj^aratus for, producing electrical undulations upon thf" Mne wire. The distinction between an undulating and a pu...aory cur- rent will be understood by ccjusidering that electrical pulsations are caused by sudden or instantaneous changes of intensity, and that electrical undulations result from gradual clianges of in- tensity exactly analagous to the changes in the density of air bell's specification. 207 occasioned by simple pendulous vibrations. The electrical move- ment, like the aerial motion, can be represented by a sinusoidal curve or by the resultant of sovcrul sinusoidal curves. Intermittent or jnilsatory and undulatory currents may be of two kinds, accordingly as the successive impulses have all the same polarity or are alternately positive and negative. The advantages I claim to derive from the use of an undulatory current in place of a merely intermittent one are, first, that a very much larger number of signals can be transmitted simul- taneously on the same circuit ; second, that a closed circuit and .single main battery may be used; third, that communication in both directions is estaljlished without the necessity of special induction coils; fourth, that cable disi)atches maybe transmitted more rapidly than by means of an intermittent current or by the methods at present in use ; for, as it is unnecessary to discharge tile cal)le before a new signal car be made, the lagging of cable signals is jn'cvented ; fifth, and that as the circuit is never broken, a spark-arrest(3r becomes unnecessary. It has long been known that when a permanent magnet is caused to approacli the ])ole of an electro-magnet a current of electricity is induced in the coils of the latter, and that when it is made to recede a current of opposite polarity to the finst appears upon the wire. When, therefore, a permanent magnet is caused to vibrate in front of the ])ole of an electro-magnet an undulatory current of electricity is induced in the coils of the electro-magnet, the undulations of which correspond, in rapidity of succession, to the vibrations of the magnet, in ])olarity to the direction of its motion, and in intensity to the amplitude of its vibration. 'Jliat tlio difference between an undulatory and an intermit- tent current maybe more clearly understood, I shall describe the condition of the electrical current when the attcmj)t is made to transmit two musieal notes .simultaneously — first upon the one plan and then upon the other. Let the interval between the two sounds be a major third ; then their rates of viV)ration are in the ratio of 4 to 5. Now, when the intermittent current is useil, the circuit is made and broken four times by one transmitting 208 THE SPEAKIXCt TELEPHONE. instrument in the same time that five makes and breaks are caused by the otlier. A and B, figs. 1, 2 and 3, represent the intermittent currents ])rodueed- four impulses of B being made in the same time as five impulses of A. c c c, etc., show where and for Ikjw long the circuit is made, and d d d, etc., indicate the duration of the breaks of the circuit The line A and B shows the total effect upon the current when the transmitting instruments for A and B are caused simultaneously to make and break tlie same circuit The resultant effect depends very much upon the duration of the make relatively to the break. In fig. 1 the ratio is as 1 to 4 ; in lig. 2, as 1 to 2 ; and in fig. 3 the makes and breaks are of equal duration. The combined effect, A and B, fig. 3, is very nearly equivalent to a contimious cur- rent. When many transmitting instruments of different rates of vibration are simultaneously making and breaking the same circuit, the current upon the main lines becomes for all practical purjKises continuous. Next, consider the effect when an undulatory current is em- ployed. f]lectrical undulations, induced by the vibration of a body capable of inductive action, can be represented graphically, without error, by the same sinu.soidal curve which expresses the vibration of the inducing body itself, and the effect of its vibra-'' tion u})on the air; for, as above stated, the rate of oscillation in the electrical current corresponds to the rate of vibration of the inducing body — that is, to the pitch of the .sound produced. The intensity of the current varies with the amplitude of the vibration — that is, with the loudness of the sound ; and the polarity of the current corresponds to the direction of the vibrat- ing body— that is, to the condensations and rarefactions of air produced by the vibration. Hence, the sinusoidal curve A or B, fig. 4, represents, graphically, the electrical undulations induc(?d in a circuit by the vibration of a body capable of inductive action. The horizontal line a d e/, etc., represents tlie zero of current The elevation h bh, etc., indicates impubsesof positive electricity. BELT. S SPECIFICATION. 20& N6.174.465i A. a. BELL JSheels-SkeMl. Ttleatei Ksiicli 7. 1676. A £. tt £. d £<*£.«^«. r't'^.i JB - X«B-« -— A _. B _ J^'iif Z. JB _ y-ufS. y''^.«' "dx^xK^^ i ^^ AtB, A-f :Fof.s: irttHrsseti /Vj/. 99. ^> TnvenTbr) ^'/'^^^UJ^ 210 THE SPEAKINCt TELEPHONE. Sb. 174.465. A. Q. B£LL. TELSOSAFBT. Fig 6. Ptttntil Mitcli 7. 1876. IFiff./ UritHcsms XnvenZOr* Fig. 100. UKI>L S .Sl'ECIFICATION. 211 Tiic depressions c c c, etc., sliovv impulses of nc^gativc electrieity. The vertieal distance b d or cfoi any })ortion of tlio eiirve from the zero line expresses tlie intcr.sity of the positive or negative impulse at the part observed, and the horizontal distance a a indicates the duration of the electrical oscillation. The vibra- tions represented by the sinusoi(hd curves B and A, fig. 4, are in the ratio aforesaid, of 4 to 5 — that is, four OF('illations of B are made in the same time; as five; oscillations of A. Tiie combined elTectof \ and B, when induced simultaneously on the same circuit, is expressed by the curve A-j-B, ^o- "^t which is the algebraical sum of the sinusoidal curves A and B. This curve A-|-B also indicates the actual motion of the air when the two musical notes considered are .sounded simul- t;meously. Thus, when electrical undulations of different rates are simultaneously induced in the .same circuit, an eil'ect is pro- duced analogotis to that occasioned in the air by the vibration of the inducing bodies. Hence, the coexistence upon a tel(>- graphic circuit of electrical vibrations of ditVerent pitch is mani- fested, not by the obliteration of the vibratory character of the (•urrent, but by iieculiarities in the shapes of the electrical rnnlu- lations. or, in otiier wonls, by peculiarities in the shapes of the <'urves which rcpre.si-nt those undulations. There are many ways of producing undulatory currents of electricity, dependent for effect upon the vibrations or motions of liodies caj)al)le of inductive action. A f(>w of the nujlhods that may be employed I shall hen; specify. When a wire, through which a continiu)us current of electricity is ])assing, is caused to vibrate in the neighborhood of anc^ther wire, an undu- latory current of electricity is inducc^d in the latter. When a <'ylinder, upctn which are arranged bar magnets, is made to rotate in front of the pole of an electro-magnet, an undulatory current of ele(;tricity is induced in the coils of the electro-magnet. Undidations are caused in a (continuous voltaic current by the vibration or motion of bodies capable of inductive action; or by the vibration of the conducting wire itself in the neighbor- hood of such bodies. Electrical undulations may also be caused 212 TUE Hl'KAKlNG TKl.Kl'HONK. by alternately increasiii<^' and diminishing tlie resistance of tlio c'ircnit, or liy alternately incn-asingaiid diniinisliing the jiower of the battery. TIk; internal resistance of a Lattery is diminished by hrlnging th(^ voltaic elements nearer together, and increased by placing them fartlu'r apart. The reci])rocal vibration of the elements of a battery, therefore, occasions an undulatory action in the voltaic current. The external resistance may also bo varied. For instance, let mercury or some other liquid form part of a voltaic circuit, then the more deejay the conducting wire is immersed in the mercury or other liquid, the less resist- ance does the licpiid offer to the passage of the current, irenee, the vibration of the conducting wire in mercury or other liipud included in the circuit occasions undulations in the current. The vertical vibrations of the elements of a battery in the liquid in which they are immersed produces an undulatory action in the current by alternately iucreasing and diminishing the jwnver of the liattcry. In illustration of the method of creating electrical undulations, I shall show and describe one form of apparatus for producing the effect. I prefer to em]iloy for this ])urpose an electro-magnet A, fig. 5, having a coil upon only one of its legsi. A steel sjjring armature c is iirndy clamped by one extremity to the uncovered leg d of the magnet, and its free end is allowed to project above the pole of the covered leg. The armature c can be set in vibration in a variety of ways, one of which is by wind, and, in vibrating, it ])roduces a musical note of a certain delinite pitch. When the instrument A is placed in a voltaic circuit, g h efg, the armature c becomes magnetic, and the polarity of its free end is op()osed to that of the magnet underneath. So long as the ar- mature c remains at rest no effect is produced upon the voltaic current, but the moment it is set in vibration to produce its mu- sical note a powerful inductive action takes place, and electrical undulations traverse the circuit g h efg. Tin; vibratory current ])assing through the coil of the electro-magnet/causes vibration in its armature A, when the armatures c h of the two instrumentii A I are normally in unison with one another ; but the armature /* IJKLL S SI-KCIKICATIOX. 218 is unaflecttvl Ijy tlie ])assag(' of tlic iuiiluliit) for which any pretenc(! can be set uj) that it is a talking telephone. Speaking of this instrument, Pi-ofessor Bell says, that Mr. Wat- 21 fi TllK SJ'KAKIN(i- 'I'Kl-KI'IloNK. Fvj. 102. ORAY S CAVEAT. 217 son, wliilc tryiii,^ it witli liim, declared tliut "lie Iniinl :i faint souikI" from it, l)iit Professor Bell could not vcrifv his iissertioii. Xow, the " fniiit sound "' heard liy ^^r. Watsoii cannot Ik; claimed to lie articul.,;e speech, and tiie |ierson who lirst olitained arlicu- lat(i uttei'ance from the lelephono is the discoverer. Mr. Oniy's a\i'at of the same date si lows niciins ot pi'oduenii' av rticulate s|iccch teli'|ihonically (li;.''. I(i2). and states that "it will (muhle |iiison.s at a distance to converse with each otliM- ihroujfh a telc- jrrapliie I'ircnit, just us they now do in each other's ])reaence, or throu^ii a sjieakinLC tul. IJeferrinjf to Prof. Rell's descri[ition, on ]k\isg 71, of the instru- ment with which lie iirst ol)tained audil)le eU'ects (lijf. ijO), it will lie seen that it is precisely the same in jirinciple, and almost identical in construction, with the receiving instrument ."^h own ind (tescri bed in ^fr. Gray's cav(>at of Fehruary 14, ISTH. Prof. Pell, it is claiii ilitaineil his lirst audil>le soiimls of articulate spei'ch in the spring' of 1870. Here, then, are two important facts bcaiMiig on the ([U("stioii of priority in the invention of the speaking tele])lione. Mr. (iray dcscrihcil ami illustrated his .speaking telephone in the winter of ls70. In the following spi'ing Prof. Bell obtained his iirst audilile eiVeets in the repro- ducti(jn of articulate speech at a distance by electro-magnetism, asnd crn])loyed for this ])ur])o.«e an apparatu.s similar to that w m lich was illustrated and described in ^fr. (Jray's cav(>at, tiled the I'nited States Patent OfTico the jireceding Febniary. Whether or not Prof. Bell inv(>nted the ap]>aratus independently of Mr. Grav, we have no means of juilgine'; but that ho was not the iirst inventor, we thiidc the facts conclnsivelv si low. Ihi Le been the iirst to inv(Mit it, is thei'c anv i 'casou w hv 1 iC SllOUl( no t hav(! described it in IIS 4'1 ilication filed: iniUitaueousJv with Mr. (Irav, on tlus 1-ith of Pobruarv, 1«76: CIIAPTER VI. EDISOXS TEI.KI'HOXIC KKSEAUCIIES. The followiii'' fominmiicutiou from Mr. Thomas A. Edison gives a detailotl account ot" his researches in telephony, and is a valuable contribntion to the history of the dovelopnieut of the speaking tclei)hone. Some time in or about the niontli of July, 1875, I began experimenting with a system of mvdtiple telegraphy, which had for its basis the transnussion of acoustic vibrations. Being fur- nished, at the same time, by Hon. William Orton, President of the AVestern Union T(>lcgraph Company, with a translated description from a foreign seientitic journal of lieisss^ tel<>phone, I also began a series of experiments, with the view of producing an articulating telephone, carrying on both series simultaneously, by the aid of my two assistants, Messrs. Batchclor and Adams. With regard to the multiple telegrajjli 1 will say that many methods were devised, among which may be mentioned the transfer system. This consi.sted in cond)ining a largo tuning fork with multiple foi'ks, so arranged at two terminal stations, with contact springs leading to diil'erent Morse instruments, that the synchronous vibrations of the forks would change the main line wires from one .set of instruments to other sets at both sta- tions, at a r.ate of 120 times ])er .sectrnd. AVith this rate of vii)ra- tion the wire would be simultaneously disc(jimected at both ter- minal stations from ouo set of ^[orse signalling a|)[)ai'atus, .'ind momentarily placeil in alternate comiection Avitii three other similar sets of a])paratus, and tiicn again returned to tiie lirst set, witliout I ..using the ap[)aratus to mark theabsenceof the current otherwise than by a percc[itil>h; weakening of the same. 1 Zeit«olirift ties DiMltscli-Oestorreicliidolii'li TeU'tfruplu-n-Viircins, lu'raiisf^'ctrebeii in (lessen Aiiltrat;!' von dvr Kr.ni^'licli I'nnissisclicn TL'lc!,'raplicM-I)in rliuTi. l{cili- trirt vim Dr. J'. Willicliii Hrix. Vol. ix., Iwi'j, puj^u jL'fi. (For ii descrijitiyii ol' Uuisu's ;4 |)iiratUH HCM' [.iijios '.> t') l-'t, ilR'lilrtivu.) TELEI'HOXIO RECEIVERS. 219 By tliis means, therefore, four perfectly independent wires were praetically created, npon which signalling could be carried on with any system which was worked no faster than the ordi- nary ^lorse system. Each of these wires was also duplexed and found to wcn-kpert'ectly upon a line of artificial resistancie, thus allowing, with the ordinary apparatus, of the simultaneous trans- mission of eight different messages. Notwithstanding the })erfect success of the system upon an artificial line, however, which posses.sed little or no electrostatic capacitv, I have never, in practice, heen ahle to prodvu'e a sufli- ciently perfect compensation for the effects of the static charge UNE Fitj. lo;!. to allow (if llic successful use of the system on a line of ovci' forty miles in length, although 1 have i)ut the line to earth at both stations after it leaves one set of instruments and before it is })laced in contact with another set; have .sent reversed currents inlci it, and have also used magnelic and condenser compensation ill Narious wavs, knov.'u to experts in static compensation, but all without avail. I\v vibrating tlu! line win^ betweiMi two .sets of apparatus, liowcxer, good satisfaction has been ol)tained on lines of about 200 niih s in length. In my system of acoustic transmission, wliich was devi.sed in September, 1875, and is shown in tig. 10.'?, two tuning fcirks, A 220 TIIK SPEAKING TET.EPIIOXE. and B, vibrating from 100 to 500 times per second, were kept in continuous motion ])y a loctil magnet and battery, and tlic sliort circuiting was controlled l)y the signalling keys Kj and Kg- As will bo seen on reference to the figure, this system, like that shown in my patent of 1873, is dependent ujjon tlic vary- ing resistance occasioned hy employing a movable electrode in water, and which thus produces corres])onding variations of the battery current in the lino. The re(!eiver3 11^ and Eg, fig. 104, were formed of telescopic tubes of metal, by lengthening or shortening of which the column of air in cither could be adjusted to vibrate in unison with the LINE Fi'j. nil. proj'cr tmic of the fork, whose signals were to ]h\ I'cceived bv each particuhir instrument. An inoi diaplu'agm M'as soldered to one end of these tul)cs. and the latter ])!ai'eil in sui'h a manner as to bring the dia[)hragm of each resju'ctively just in front oi'an ekv tro-magnet, which, in action, would cause them to viiinite. When the column of aii' in cither receiver was jiroper'y adju.st(>d to a gi\(m tone, the signals due to sto]i])iiig and starting the vibrations by the distant key were very jond, as compared to other tones not in harmony with the column of air. FN \ililc rubber tubes, with car pieces, wci'(^ connected to thi' I'cceiviM's, so MAGNETO-SPEAKING TELEPHONE. 221 that, in usiiif^f the instruments, llie liead of the operator was not re([uired to be held in an unnatural or strained position. This system worked very well ; but one defeet in it was apparent fi'oin the lii>;t, and that was its continual teiulcney to give the operator what is termed the baek-sti'oke, even from the slightest cause, such as the opening of a door or the moving of the head, and also occuiTed on the slightest inattention whatever. With a Morse sounder, as is well known, every dot is made apparent to the ear by two sounds, the first being produced when the lever strikes the anvil, and the other wlieu it strikes the; nppcr or back contact. A dash, like the dot, is als(j composed of two sounds, l)ut the interval of time between the pi'oiluction of tlie first, the downward stroke orsouud and the U])ward stroke, is what determines its character. Jt fi'cMpiently happens, Jiow- evcr, when a sounder is so adjusted that the .sound produced by the down stroke is of the same volume or loudness as the one given by the up stroke, that the order of reading becomes re- versed on the slightest disturbance or iiuittcntion and the ear nustakes the up .sound for the dov/n .sound, and vice versa. The signals conseipiently become unintelligil)le, and the operator can only restore the; proper ()r(h>r ])y closing botii cars and watching ■he motion of the sounder lever, or by deadening the back sound iv ]»laeing the finger on the lever until the ear again catches a ^' rd or two. Similarly with the musical signals, the dots and dashes are I'oiined by the relative short or long duration of a continuous tone, l)ut in this ca.se the pitch is always the same, and this con- .stitutcs an element of confusion that is qnit(! as bad as tlu^ back stroke of the sounder above rcfeiTcd to. J therefore arranged my keys so as to tiunsmit two short tones close together to form a dct, and two tones separateil by an interval to form a dash : but there was still so little distinctive difi'ercnce between one and the other that J was led to defer further expcrinu-nt with the appa- ratus for a time. It is probable that soiuc! means will be fouiid for ])rodu( ing a greater degree of difrert'nce between the two ele- ments of the signals, such, for instance, as the employment of two 222 THE SPEAKING TELEPHOXE. forks of slightly different ])itfli, which, at least, i)romises well. When this is done the system will be of some value. It will he noticed that tlie receiving instrument shown in fig. 104 CDutnins the diaphragm magnet and chaml)er of the magneto- speaking '• 'r le; and I may say liere that Iljclievel was the first to devi. u'atus of this kind, which I intended for use in connection win eoustic telegrajths. I tan, however, laynoclaim to having; discovered that convci'sation could he cairied on Ix;- tween one receiver and the other upon the magneto principle by causing the voice to vibrate the (liai)hragm. Another system of niuitiple transmission consisted, partly, in the use of reeds for receivers, and has been exceedingly well de- veloped in the hands of Mi\ Klislia tii'ay, but I f()rbear explain- ing it here, owing to its complexity and lack of practical merit My first attempt at constructing an articulating telephone was made with the Reiss transmitter and one of my i-csonant receivers described above, and my experiments in tliis direction, wliich continued until the production of my j)rescnt carbon telcj)honc, cover many thousand pages of manuserij)t, I .shall, however, describe here only a few of the more imporkmt onc-^. In one of the llrst experiments I included a simplified Reiss transmitter, having a platinum .screw facing the diaphragm, in a circuit containing twenty cells of battery and the resonant re- ceiver, and then placed a drop of wat(>r between the points; the results, however, when the apparatus was in action, were unsatis- factory — rapid decomposition of the water took iilace and a de- posit of sediment was left on the platinum. I afterwards u.sed disks attached both to the diaphragm and to the .scnnv, with sev- eral drops of water [jlaced between ami held there by capillary attraction, but rapid decomposition of the water, which was im- pure, continued, and the words came out at the receiver very much confused. Various acidulated .solutions were then tried, but the confused .sounds and decompositions were the only results obtained. With distilled water I could get nothing, ])robably because, at that time, 1 usc(l very thi(;k iron diaphragms, as 1 have since ■ THE CAKBON TELEPirONE. 223 frequently obtained good results ; or, jjossibl y, it was because the ear was not yet educated for this duty, and therefore I did not know wliat to look for. If this was the case, it furnishes a good illustration of the fact observed by Professor Mayer, that we often fail to distinguish weak sounds in certain cases when we do not know what to expect Sj)onge, i)a})er and felting, saturated with various solutions, were also used between the disks, and knife edges were substi- tuted for the latter with no better results. Points immersed in electrolj'tic cells were also tried, and the experiments with vari- ous solutions, devices, etc., continued until February, 1876, when I abandoned the decomposable fluids and endeavored to vary the resistance of the circuit j)roportionately with the amplitude of vibration of the diaphragm by the use of a multiplicity of plat- inum points, springs and resistance coils— all of which were de- signed to be controlled by the movements of the diaphragm, but none of the devices were successful. In the spring of 1876, and during the ensuing summer, I en- deavored to utilize the great resistance of thin films of plumbago and white Arkansas oil stone, on ground glass, and it was here that I first succeeded in conveying over wires many articulated seiit^'nccs. S})rings attached to 'he dia[)hragm and numerous other devices were made to cut in and out of circuit more or less of the plumbago lilm, but the disturbances which the devices themselves caused in the true vibrations of the diaphragm pre- vented the realization of any practical results. One of my as- sistants, however, continued tiic experiments without intcrru]>- tion until January, 1877, when I a})plied the peculiar property which semi-conductors have of varying their resistance with ])ressur(', a fact discoverecl by myself in 1873, while constructing .some rheostats for artificial cables, in which were emj)loyed powdered carbon, plumbago and other materials, in glass tubes. For the })urpos(^ of making this ai)[)lication, L constructed an apparatus ju-ovided with a diaphragm carrying at its centre a yielding spring, which was faced with platinum, and in front of this I placed, in a I'up seeui'cd to an adjusting screw, sticks of 224 THE SPEAKING TELEPHONE. crude plumbago, coiubiiied in various proportions witli dry Jiow- ders, resins, etc. By this meaiis I succeeded in producing a telephone which gave great volume of sound, but its ai-ticuhition was rather poor; when once familiar witli its peculiar sound, however, one ex^ierieuced but little difliculty iu understanding ordinary conversation. After conducting a long series of experiments with solid ma- terials, I finally abandoned them all and sul)stitutcd therefor tufts of conducting fibre, consisting of lloss silk coated with plumbago and other semi-conductons. The results wei'e then very much better, but wliile the volume of sound was still great, the articulation was not so clear as that of the magneto tele- phone of Prof. Bell. 'J'he instrument, besides, rcipiired very frequent adjustment, which constituted au objectionable feature. Upon investigation, the difference of resistance produced by the varying pressure upon the semi-conductor was found to be exceedingly small, and it occurred to me that as so small a change in a circuit of large resistance was only a small factor, in the primary circuit of an inducti(jn coil, where a slight change of resistance would be an impf)rtant factor, it would thus enable me to obtain decidedly better, results at once. Tlie experiment, however, failed, owing to the great resistance of the semi-con- ductors then used. After further experimenting in various directions, I was led to believe, if I could by any means reduce the ncjrmal resistance of the semi-conductor to a few ohms, and still effect a difference in its resistance l)y the pressure due to the vibrating diai)hragm, that I could use it in the primary circuit of an induction coil. Having arrived at this conclusion, I constructed a transmitter in which a button of some semi-conducting substance was placed between two platinum disks, in a kind of cup or small containing vessel. Electrical connection between the button and disks was maintained by the slight pressiire of a piece of rubbei- tubing, J inch in diameter and ^ inch long, which was secured to the dia- phragm, and also made to rest against the outside disk. The vibrations of the diaphragm were thus able to produce the THE CARBON TKLEPHONE. 225 requisite pressure on the platinum disk, iind thereby vary the resistance of tlie button included in the primary circuit of the induction coil. At fii-st a button of solid plumbago, such as is emplo\-ed by electrotypers, was used, and the results obtained \v(>r(; considered excellent, everything transmitted coming out moderately dis- tinct, but the volume of s(jun(l was no greater than that of the magneto telephone. In order, therefore, to obtain disks or buttons, which, with a low normal resistance, could also be made, by a slight pressure, to vary greatly in this respect, 1 at once tried a great vai'iety of substances, such as conducting oxides, siUjihides and other par- tial cstigation, that the resistance of the disk could be varied from three hundred ohms to the fractional part of a single ohm by jiressure alone, and that the best results were obtained when the resistance of the itrimary coil, in which the carbon disk was included, was -j-\ of an ohm, and the normal resistance of the disk itself three ohms. Air. Henry Bentlev, ]ir(>sident of the Local Telegraj)h Com- jiany, at Philadelphia, who has made an exhaustive series of experiments with a complete set of this apparatus upon the wires of the Western Union Telegraph Company, has actually succeeded in working with it over a wire of 720 miles in length, and has found it a practicable instrument upon wires of 100 to 2()0 miles in length, notwithstanding the fact that the latter were ]>laced upon poles with numerous other wires, wliich occasioned sufTiciently powerful induced currents in them to entirely destroy the articulation of the nuigneto telephone. 1 also learn that he has found the instrument practicable, when included in a Morse 226 THE SPEAKING TELEPHONE. circuit, witli a battery and eiglit or ten stations provided witli the ordinaiy Morse apparatus ; and that several way stations could exchange business tclcphonically upon a wire ■\vhicli was being worked cpiadruplex without disturbing the latter, and not- withstanding, also, the action of the powerful reversed currents of the quadru})lex on the diaphragms of the receiver. It would thus seem as thougli the volume of sound produced by the voice with this apparatus more than compensates for the noise caused by such actions. While engaged in experimenting with my telephone for the pur- pose of ascertaining whether it might not be ])ossible to dispense with the rubbc' tube which connected the diaphragm with the rheostatic disk, and was objectionable on account of its tendency to become flattened by continued vibrations, and thus necessitate the readjustment of the instrument, I discovered that my prin- cijile, unlike all other acoustical devices for the transmission of speech, did not require any vibration of the diaphragm — that, in fact, the sound waves could be transformed into electrical pul- sations without the movement of any intervening mechanism. The manner in which I arrived at this result was as follows: I first substituted a spiral spring of about a quarter inch in length, contiiining four turns of wire, for the rubber tube which connected the diaphragm with the disks. I found, however, that this spring gave out a musical tcme which interfered somewhat with the clfects produced by the voice ; but, in the hope of over- coming the defect, I kept on substituting spiral springs of thicker wire, and as I did so I found that the articulation became both clearer and louder. At last I sul)stituted a solid substance for the springs that had gradually been made more and more inelastic, and then I obtained very marked improvements in the results. It then occurred to me that the whole question was one of pres- sure only, and that it was not necessary that the diaphnigm should vibrate at all. I consequently put in a heavy diaphragm, one and three quarter inches in diameter and one sixteenth inch thick, and fastened the carbon disk and plate tightly together, so that the latter showed no vil)ration with the loudest tones. THE CARBON TELEPHONE. 227 Upon testing it I found iny snrrnirtes veviiied ; tlic articulation •was perfect and the volume of sound so great that conversation carried on in a whisper three feet fi-oin the telephone was clearly heard and understood at tlie otlier end of the line. Tiiis, therefore, is the arrangement I liuve adopted in my pres- ent form of a]-)parat)is, which I call the carbon telephone, to dis- tinguish it from others. It is fully described in another part of this work. The accessories and connections of this apparatus for long cir- cuits are shown in lig. 105. A is an induction coil, whose jiriraary Fig. 105. wire p, having a resistance of several ohms, is ])laccd ai'ound the secondary, instead of within it, as in the usual manner of con- struction. The secondary coil s, of finer wire, has a resistance of from 150 to 200 ohms, according to the degree of tension re- quired ; and the receiving telephone R consists simply of a mag- net, coil and diaphragm. One pole of the magnet is coimceted to the outer edge of the dinphragm, and the other, wliich carries the wire bobbin of about 75 ohms resistance, and is included in the main line, is placed just opposite its centre. 228 THE SPEAKING 'J'KLEl'JIOXE. P E is the signalling relay, generally a SicMnens' polarized in- strument, which has been given a bias towards one side, and (!on- sequently is capable of rcsi)oiiding to currents of one delinite direction onl}^ The lever of this relay, when actuated by the current from a distiuit station on the line in which tlie instrument is included, closes a local circuit containing tlie vibrating call bell B, and thus gives warning when S2)eaking communication is desired. Besides serving to opei-ate the call bell, tlie local l)attery E is also used for sending the call signal. S is a switch, the lever of which, when placed at o, between miind «, disconnects the trans- mitter T and local buttery E from the coil A, and in this posi- tion leaves the polarized relay P E free to respond to cur- rents from the distant station. When this station is wanted, however, the lever S is turned to the left on ?i, and depressed sev- eral times in rapid succession. Tlie current from the local bat- tery, by this means, is made to jiass through the primary coil of A, and tluis for each make and break of tlic circuit induces powerful currents in the secondary s, which pass into the line and actuate the distant call bell. When the call signals have been exchanged, botli terminal stations place their switches to the right on m, and thus intro- duce the carbon transmitter into their respective circuits. The changes of pressure, produced by sjieaking against the diaphragm of either transmitter, then serve, as already shown, to vary the resistance of the carbon, and thus ])roduce corresponding varia- tions in the induced currents, which, acting through the receiv- ing instrument, reproduce at the distant station whatever has been spoken into the transmitting instrument. For lines of moderate lengths, say from one to thirty miles, another arrangement, shown in flg. 106, may be used advantage- ously. The induction coil, key, battery, and receiving and trans- mitting telephones, arc lettered the same as in the previous figure, and are similar in every respect to the apparatus there shown ; the switch S, however, differs somewhat in construction from the one akeady described, but is made to serve a similar purpose. TEI-EI'IIONE SIGNALLING APPARATUS. 229 When a jiliig is inserted between 8 ami 4, tlie relay or sovinder E', battery E, and key K only arc included in the main lino circuit, and this is the normal arrangement of the apparatus for signalling purposes. The battery, usually about three cells of the Daniell form, serves also both for a local and main battery. "When a plug is inserted between 1, 2 and 4, the apparatus is available for telephonic ctommunication. I have also found, on lines of from one to twenty miles in length, that the ordinary call can be dispensed with, and a sim- plified arrangement substituted. Tliis latter consists simply of the ordinary receiving telephone, Tipon the diaphragm of which a free lever, L, is made to rest, as shown in fig. 107. When the induced currents from the distant station act upon the receiver K, the diajihragm of the latter is thrown into vibration, but by itself is capable of giving only a comparatively weak sound ; with the lever resting upon its centre, however, a sharp, penetrating noise is produced by the constant and rapid rebounds of the lever, which thus answ(>rs very well for calling jjurposes at stations where there is comjuiratively but little noise. 230 THE STKAKINIi TEl.Kl'lli iNK. Among tlic various otlim' m(>tli(i(ls for si<;;ii.illiiig ])urposos wliicli I huvo ex pori merited witli, I may mciilioii tlio sounding of ii note, by tliu voice, in a small lieisss tele[ili()nc; the emjiloy- mcnt, of 11 seU'-vihrating reed in the local circuit; and a break wheel with many cogs, so arranged as to interrupt the circuit when set iu motion. Rg. 107. I have also used direct and induced currents to release clock work, iind thus operate a call, and in some of my earlier acou.stic ex{)eriments tuning forks were used, who.se vibrations in front of magnets caused electrical currents to be generated in the coils surrounding the latter. By the further action of these currents on similar forks at a distant station, bells were caused to be rung, and signals thus I" n. Fig. 108. given. Fig. 108 shows an arrangement of this kind. A and B are two magnetized tuning forks, liaving the same rate of vibration and placed at two terminal stations. Electro-magnets m and m* are placed opp.osite one of the p>rongs of the forks at each station, while a bell, or D, stands opposite to the other. The coils of the magnet are connected respectively to the line ELECTRO-STA'l'lO TKLEPUOXE. 281 wire and to ciirlh, Wlicu one of tlio forks is set in vibration by a sturtin;^' kt-y jn-ovided for tiio pui'])os(,', tiio currents produced by the apin'oarii of oik; of its magnetized prongs towards tla^ magnet, and its recession tiiercfroin, pass into the line and to tiie furtlier station, whi'rc tlieir action soon causes tlie second fork to vibrate witli constantly increasing amplitude, until the bell is struck and the signal given. LJ3 Fiij. 109. For telephonic calls the call bells arc so arranged that the one opposite to the fork, wiiicli generates the currents, is thrown out of the way of tiie hitter's vibrations. Another call apparatus, which I have used, is represented in fig. 109. In this arrangement two small magnetic ])endnlums, whose rates of vibration are the same, are placed in front of l^XE IT Fi ]icrl'ect as for the electrophorous ajiparatu.s. Fig. 112 shows a form of cleetro- mcchauieal teleplnme, referred to near the beginning of this eomnnmieatii)ii, by means of which I attempted to transmit electrical impulses of variable strength, so as to reproduce; spokcMi words at a dislani'c. Small resistance <'oils — -1, 2, l), etc. — were so arranged with connecting s[)rings near a jilatinmu faced lever :3 THERMO-KLECTUIC TELEPHONE. 288 B, in connection with tlic diaphragm in A, that any movement o[ the latter caused one or more of tlic coils to be cut in or out of the primary circuit of an induction coil C, the number, of course, varying with the amplitude of tlie vibrating diaphragm. Iiubiced currents corresponding in strengtli with the variations of resistance were thus sent into the line, and could then be made to act upon an ordinary receiving tele])lione. By arranging the Fij. 112 springs in a sunflower jiattcrn about a circular lever, I have suc- ceeded in transmitting articulate sentences by this method, l)ut the results wen; very harsh and disagreeable. Fig. 11.'^) shows a form of the water telephone ])rcviously re- feiTcd to, in which a double cell was u.sed, so as to afford con- siderable variation of resistance for the very slight movements B Lim m Fig. n.-?. of t1ie diaphragm. The action of the apparatus will readily be understood from the figure, where a win; in the form of the; letter IT is shown, with the bend attacheil to the dia|)hi'agm, and its ends flipping into tin; sepanite cells, ami thus made to form part of lh(! circiiit when the lim^ is joined to the instrunn'ut at a anil c. I am now conduclnig experiments with a thermo-eleetric tele- 284 THE SPEAKING TELEPHONE. ])hone, wliicli gives some premise of becoming serviceable. In this aiTaiigemeut a sensitive tliermo-pile is placed in front of a diapliiagm of vulcanite at each end of a line wire, in the circuit of which are included low resistance receiving instruments. The principle upon whicli the apparatus works depends upon the change of temperature produced in the vibrating diaphragm, whieli I have found is iiiucli lower as the latter moves forward, and is also correspondingly increased on the return movement Sound waves are thus converted into iK'at waves of similar characteristic variation.s, and I am iu hopes that I mayultimat(;ly bo able, by ihv. use of more sensitive thermo-piles, to transform these heat waves into electrical currents of sutricicnt strength to. ])roduce a practical tc]cj)hone on tliis novel iirineiplc. Before concluding, I must mention an interesting fact con- nected with teleplionic transmission, wliich was discovered during some of my e.\i)eriinen1s with the magneto-telejthone, and wliich is this, tliat a copper disk may be substituted lor the iron dia- phragm now universally used. The same fact, I believe, has also been announced by INfr. W. 11. Preecn;, to the Physical Society, at London. If a piec(; of copper, say one sixteenth of an inch thick and three fourths of an inch in diamctei', is secured to the centre of a \ideanite diaphragm, tlu; effect becomes ipiitc marked, anrilliant series, v.'hich 'A paiuT rc'iul lu't'iiru tlio atiniiiil luoetiiitf i>f tlio AiiuMMciiii Elooirioal Society, at (-liicaifo. 111., DiH'omlior lii, 1877, Ijy t\ h. I'opo. Jouriial of tlio Amoricuu Klou- trieal Sooicty, vol. i., No. 3. 236 THE SPEAKING TELEPHONE. have justly rendered the name of Galileo forever immortal in the annals of seicnco and of history. In order that wc may arrive at a clear understanding of the principles underlying tlie dilfereut varieties of the telephonic, or, in more general terms, the electro-harmonic system of teleg- raphy, and that we lUiiy be ahle to trace intx^lligently its origin and development, it is essential that we should first l)ecorae s(Mnewhat aerpiainted with the laws and leading phenomena of vibratory or undnlatory nioti(Mi in general. Having done this, we shall find no dilheulty in ])assing to the consideration of the special practical apjilications of these laws, which have recently been made in the domains of electro-telegraphy and electro- acoustics, and whii'li have Ijcen attended with such remarkably brilliant and successful results. Let us consider for a moment some of the peculiar ])roperties of a body freely susjiended from a fixed point — in other words, a pendulum, i sup})0se there are not many here present who do not treasure among the happiest memories of childhood the associations connected with the swing. It was simply a seat suspended l)y two ropes, pei'hai)S from the horizontal branch of some overshadowing tree. I shall probably bo safe in assuming that yon all have a tolerably viviil n^colleetion of most of the phenomena presented Ijy this mechanical contrivance when in active operation ; a \ itv fori iniaic circumstance, inasmuch as it will enable me to ])lacc clearly before your mind.s some of the most important of the fumlameiital laws of vibration. Wln'n our friend ti 10 scnoiili)ov. navinii sea ted out! o f hi.S youthful fa\-orit(vs in the swing, ami by a scries of judiciously timed impulses gradually increased the amplitude of her oscilla- tions from zero to ])crliaps 120'' of arc, proceeds, in compliance with her breathless reipu'st, to discontinue his exertions, and, in the classic language of the play-ground, to '' let the old cat die,'' it is hardly sur[)rising that, not being aiii.uer (ialileo, our young friend has utterly faileil to grasp the great ))hysical ti'uth that the vibrations of the little, maiden are isochri)nous. Still h'ss does he probabl}' suspect that, even \' en; ho to subject the very PROPERTIES OF THE PENDULUM. 237 pchoolma'ain hcrsolf to tlic same conditions, the periodicity and the isoclironisni of lier osciUations would not difFcr from those of her predecessor, notwithstanding tlie much greater weight of the oscillating hody. Nevertheless, such is the fact. It is one whicli was experimentally demonstrated many years ago — ])y myself, althougli, of course, it would hardly l)c becoming for me to claim ab.solute priority over all others in making the experi- ment. Another imj)ortant property of tlie pendulum is that, by shortening it, it oscillates more rapidly. Thus, if we take two penduhims, one of which is three and the other twelve feet in length, the shorter pendulum will be foimd to make two oscil- lations to each ono of the longer one, and if wcs continue the experiment with ]>cndulums of difTercnt lengths, we shall arrive at the law that the time re([uirc(l in each case to jierform an oscillation is jjroportional to the scjuare root of the length of the pendulum. I will also call attention at this point to a third property of the vibrating ])(;ndulum, which it will bo very important for ns to remember, in view of what we shall come to further on; a property whicli is very well illustrated by the suspended swing, to which T hax'c just referred. It is this : A freely suspended body, even if it bo very heavy, may l)e set in vibration by the rei)cated application of a comparatively insignificant force, pro- vided tlic successive applications of the force 1)0 properly timed, but not otherwise. Of cour.se you hav(! all noticed this in the case of the swing, and therefore I need not enlarge upon it fur- ther than to say that the same elTeet is ])roduced, though in a less degree, no matter whether the impulses are given at every vibration, at every alternate vibration, or even less friMpiently. The essential condition i.s, that the intervals of time between the successive iin[)ulseg shall be exactly the same as the intervals between the vibrations, or cLse a multiple or submultiplo of ono of these intervals. I have made use of tho suspcndeil ]i(>ndulum to illustrate some of the principal laws ot vibratory motion, for tho reason 238 rilK SI'KAKIN(t 'J'KI-KI'IIOXK. that its ]ilu'nomona aro faiiiiliar to ysi nts itsclt throughont the realm of physic*?!. All solid bodies exhibit the ])henomena of vibration in various forms and degree.s, aeeording to the form of the body and tlic manner in which the force producing tlie vibration is ajiplicd. Cords and wires, as familiarly seen in striiig(>d instrument.s of music, have their elasticity developed by tension so as to become capable of vibration. If tlie cord a f h (iig. 114) l)c di-awn out in the middle to rt c i, upon being rehvised its elasticity cau.'Jcs it to return to its fornuT ])osition. The velocity of this movement is constantly accelerated, and is at its maximum when the cord Fig. 114. has reached its line of equilibrium afl; consequently, it passes with constantly decreasing velocity to a d h, wlicre it eotnes to rest for an in.stant, and then reti\nis to a f b, and so continues. You will at once ])erceive the analogy between the vibrations of the central jioint / of the string between c and d and that of the weight of the pendulum, and like those of the pendulum, the vibrations of the stretched string are isochronous. It maybe regarded, in fact, as a kind of double jiendulum, and is .subject to the same laws as the ordinary pendulum. The tension and diameter being equal, the number of vibrations })erforme(l by a cord in a given time are inversely as its length. Elastic rods vibrate laterally like cords when fixed by their extremities. In conse(iuence of tluMr rigidity, however, they may be made to vibrate when fixed only at one extremity. Thus, a straight steel rod n may be chuiiped iu a vice, as shown in Iig. 115. If we draw VIBRATINft noi)>'. 239 tho free nid 71 aside and tlion lihoralc it, it will vibrate to and fro between the jioints p and ]? as sliown by the dolled lines. Tho am[)litude of tho successive! vilirations, liowcvcr, constantly diminishes, until at len,irth the r<>d returns to its original stale of rest. Sueli a rod, when vibrating, follows the same law as the pendulum and tlio stretched c(m\, each vibration, whether greater or smaller, being performed in tho same lengtb of time, and the number of vibrations in a givi'u time b<'ing iuversely propor- tional to the square of tho length of tko rod. P Fig. 115, Fig. tie. The onlinary tuning fork, an almost indispensable instrument in the experimental investigation of tho various ])roblcms of acoustics, consists virtually of a, doidde vibrating rortby becomes caj)able of vibrating at one par- ticular rat(!, and no other. You will see, therefore, that wo may have a succession of plates of various forms, passing by degrees from the circular ])late clarniicd at its edges, which will take any rate of vibration with e(jual facility, to the string f)r rod clamped at one or both ends, which will only take one particular rate, rejecting all others. These properties of plates of diiferent forms, in ncsjici't to their modes of vibration, are of tho utmost importance in harmonic telegraphy, as we shall hereafter see. It renuiins to speak of the vibrations of membranes, which are in iTiany respects analogous to those of ])lates. "When loosely stretched over a circidar liooj) or frame, such a Tnembranc, like tho circular ])late, has no decided tendency to vibrate at any ])ar- ticular rate. If strained more tightly, however, its tendency to vibrato at .somes particular i-ate is increased. Omitting for the pnssent a inore })ailieidai* consideration of the characteristics of vibrating solids, we will now examine the effects of vibratoiy motion upon fluids. Tyinlull — " Lucturi's on Sound" (Anicriciiii edition), ji. ISS. VIBKATORY MOTION OF KIJ'IDH. 241 If we drop a smooth, round pebble into the bosom of a placid pool, a series of concentric undulations are produced. Wave follows wave, in ever-widening circles, until opp(Jsing forces at length cause an equilibrium to bo regained. At the initial point a depression is produced by the fall of the pebble. Around this there first rises a circular elevation above the surface of the liquid when in equilibrium, and immediately beyond this is a circular depression, and so on, altciiuitely, successive elevations and depressions. When we look at this progressive series of waves, the entire mass appears to advance progressively in every direction away from the ])oint of excitation; but, if wc watch the movements of some light, flouting body, we shall sec that this body is not carried forward over the surface, but merely rises and falls alternately as the waves pass beneath it. ^Nforc- over, wc shall bo able to observe an exact analogy between the vertical oscillations of this floating body and those of the sus- jiended weight of tho pendulum, or the central point of the stretched string, thus proving that the vibratory motion which we have already exnniined, and the undulatory motion uiuhsr con- sideration, are manifestations of the same law under difTerent conditions. The undulations which wc have just described are surface waves. All elastic mediums are also subject to undulations of a totally dillerent character, which are termed waves of conden- sation and rarefaction, and are produced in air and gases by any disturbance of density. If any elastic fluid be compressed, and then suddenly released from compression, it will exjiand, and in its cx2)ansion exceed its former volume to a certain extent, after which it will again contract, and thus oscillate alternately on either side of its position of rest It must be understood that this class of nndulations extend equally in every direction from a centre toward every point of tho circumference of a sphere. This alternate condensation and expansion of an elastic fluid or medium, extending spherically around the original centre of dis turbanee, is perfectly analogous to the series of cinndar wavc-i which wc have seen formed around a point of depression on the 242 THE HPEAKIX(} TKIiEl'HONK. i surface of a liquid, tlic cuiKlcnsatioii of tlie clastic fiiiid corre- sixiiuling to the elevation of a surface wave, ami the phase of rarefaction correspondinif to the jihaso of ssi()n. Suppose liji". 117 to represent a section of a s])here of air, or other elastic mcdinni in whicli the waves of condensation ami rarefaction have extended outward from the centre (-, tiien the heavy lines aefy, h h ik ami d I]) q, will represent the phases of greater condensation, the finer int(>rniediate lines will represent the spaces of greatest rarefaction, and the distances vi n and n o, h(>tw(^en circles of greatest condensation, will be the length of the waves. Fig. m. These waves of condensation and rarefaction in an elastic medium, like the waves on the surface of a licpiid, are subject to the ordinary laws of vibration, and are capable of producing or of being produced by the vibrations of a soliil body. The nnitual eonvertiliility of vibrations and undulations may be shown by c.\})crinicnt. If a tuning fork is stnick or e.xcited ])y a violin bow and its motion allowed to gradiially die away, its prongs oscillate backward and fm-ward in the same manner and after the same law as a pendulum, except that they make niany hundred vil)rations for each single A'ibration of the jmmuIu- bim. A jiarticular tuning fork, therefore, will always perform a given number of vibrations in a unit of time. This number de- (t sa ti< nn hu VELOCITV OK SolNl). 243 pends pf>lel\' ujiori tlio constrimlioii of tlic fork, fiixl ciiii, there- fore, neitlicr lie iiicrcasv'tl iior diiniuishfil, unless IIk; form or properties of tlio fork are in Homo way cliuuged. If we tlirovv siieh a t\uiin<^ fork into vibration tlie vilirations of llie fork cause undnlatious in tlio surrounilinL' aii'. whiili uro. pro- 2)aj:ate(l in every diri'i'tioii. TTow is tliis broni^lit about,? Kacli of the ^jron^rs licats tlie air in o[)posito directions at the same time. Let us try to jiicturo to ourselves the jihysical condition of the air in front of one of tlicse ])rougs. As thtilattiir strikes out- ward the air in front of it will he driven outward, condensed, and on account of tlio elasticity of the air, the comhmsatiou will at once start to trav<4 outward in every direction a wave of denser air; hut directly the prong recedes, heating the air hack in the Fig. 118. contrary direction, which will, of course, rarefy the air in front of tlie prong. But the disturhanco wo call a rarc^factioii is ])ropagated in aii" with the saino velocity as a condiMisation. We nust therefore renicmher that just behind the wave of eon- dens^jtion there is a wave of rarefaction, each travelling with the same velocity, and then^fore always maintaining the same ])osi- tion in relation to each other. 'JMins the foi'k vibrates a certain number of times in a .second, and will consequently generate an equal number of these waves, all constituted alike and the same length. (See fig. lis.) Suppose a fork to make one hundred vi- brations ])cr second: at the end of the first s<'cond the wave geiierateil by the vibration at the beginning of the second would liavo travelled, say, eleven hundred feet (which is known to be 244 THK SI'KAKINa TELEl'HONK. approximately tlic distance traveraed in a Hecond by aerial vibra- tion), and tlio intcnncdinti! \vavc?( would be nnifi)rmly distributed over tlie int(^rveuing distani'(! ; tliat is to say, in eliiven Imndrcd feet there would be one liundnul waves, each of them evidently being eleven feet in length. IP tiie fork made elcjvcn hundred vibrations jier second, each of these waves would be oiu; foot long, for waves of all lengths traverse the air with precisely the same velocity.! Now, if we })lace in another ])art of the same room aiiotlun' fork, so constructed as to make exactly iho same Jinnil)er of vibrati(ms per second as the first one, and set the first one in vibration, the other one will soon begin to vibrate in sympathy, and it will even continue to vibrato after the first one had l)eeu .stopj)ed. Astonishing as it seems, it is nevertlailess true; that this heavy and rigid mass of steel has been set in motion merely by the successive impact of hundreds of tiny waves of air, each of sueli small motive power that it could not stir the weakest spring which was not adjust d in unison with the fork. Tim slightest disagreement in the respective rates of vil)rations of the two forks sensibly diminishes, and a dilTerenee of one vibration in two or three hundred 2)er second wholly destroys, the cffeet. Thus we SCO that the isochrf)nous vibrations of tlu; tirst fork give rise to corresponding waves or nndulations of condensation and rarefaction in the air, and these in turn rei)roduco isochron- ous vibrations in the second fork, and will also produce vibra- tions to a greater or l(;ss extent in every body which is capable of vil)rating in unison with the first fork. Thus far we have confined our attention solely to the nature and effects of simple vibrations. It remains to consider what effect is ])roo time, without mingling with each other; but, in cases where there are many ns, and this may bo readily done by the aid of the method of graphie pri^jection, which has been before ex[)lained. Tims in lig. 120, wo may suppose th ; horizontal length of the diagram to represent a unit of time. The curve A will then re[)rosent tin; undulation in the atmosphere caused by the vi- brations of a tuning-fork in acticui. The horizontal \'ed ])y Jlclmliolt/. in accomplisliing this beautiful result,^ although we shall luive occasion to refer here- after to some of the analogous means which have been employed in telegraphy for the same purpose, that is to say, the analysis of C(jmposite ■sibratory motion.s. The idea of synchronizing the movements of the two instru- ments at wi'^'ly sejiaratccl points for telegra})his were 1 For ft full ftoconnt of tlio iiiipiirutus iindinctliods emiiloyeil in tlieno cxperlmoiits, sen il)ul., Clmiitrr III. » So« .SliaH'MiT -"TcU'trrapli Miinniil," ].. 117. ' Vail — "Eloctro-iuu){iiotio Toloj^rupli," ji. l.'^'i ; Sluilfrirr -" Tuloi^rupli Maimiil," p. .182. •1 Prcspott — " History, Tlnnry ami Pruotlco of Klfclrii' Tilt'tfraiili," \k 1".',i. A1»u saiiK! aiithor'.H " Klut'trii.'ity anil Klcctno IV'K'jirai'li." i<. i>"\). 260 THE SPEAKING TELEPHONE. very ingenious and beautiful, and it is cvidonl , f rom doscriptions and ])aj)ers published at that tiniu,! ono of which lias recently been reproduced in the Journal of the lVlegra[)h, that Reiss had made a thorough study, both of the laws of electro-magnetism and of acoustics, and nndcrstood perfectly the conditions of the problem with which he undertook to deal. Sound is simply a sensation resulting" fnmi the action of vibrations upon the nerves of the ear. If the same vibrations are felt by the touch, they ]iroduce a certain i)cculiar lluttcring sensation ; but this is not sound. Therefore, although all souud.s arc neces'-arily the result of vibrations, all vibrations do not necessarily produce sound. The vil)ratory motions proceeding from soundiny bodies are nsuallv couducted to the ear throiiy;!! the medium of the atmosphere, '^i'liercfore, to produce any given sound, of whatever characti'r, at a distance, it is evidently only necessary to throw the atmosphere at tiiis point into vibration precisely similar in every respect to those which wouhl be ]->ro- duced by the action of the original source of sound, whatever it may be. It is found that all ilw. characteristics of souml which are appn-ciable by our senses depend upon three; things: Kirst, the rapiility of tlu; vibrations, which determines what we call the pitch of the sound, whether, for example, it is high or low; second, the aniiilitude of the vibrations, wiiich determines the loudness or power of the sound ; and, third, tlu! form of vibra- tion, as ri'presentcd by tlu; curve corresponding to the movement of the vibrating body, which determines the (piality of the sound. The apparatus of R;'iss consisted of a thin, stretched mem- brane, rigidly supijortcd at tlu; edges, and free to vibrate; in iIh; middle. Tiie mathematical theory of the vibration of such a membrane, having a uniform tension in all directions, shows 1 K"isa— Piiiftlor'H /hli/tfi-Jinie Journal, WA. n.XVIII.,p. is.l ; T.t'^iit Zntucftrift df> JhiitsfhiiKtirreichinelien 'JUi'irajilien IV/v/h*, Vol. I \'., ]i. l'J."i. An (.'Xi'i'llciit trii'iH- liitioii of this lust jiujiur may lio I'ouiiJ in thu Journal of the Tehijraph^ Vol. X., p. 8S3. BEISSS APPAHATUS. 251 tliat vibrations produced in any part of the membrane will pro- duce nearly as strong vibrations (disregarding individual nodal lines) in all other parts of it A thin, light membrane is not only susceptible of sympathetic vibration when vibrating air is allowed t(i act upon it, but this vibration is not limited to any particular pitch, and it is therefore capable of respDuding to sonorous vibrations of every character, traversing the atmos- phere. A delicate circuit-breaker, attached to the membrane, was arranged to break the circuit of a telegraph line at the vibration, and thus the armature of an electro-magnet at the receiving station was easily adjusted to respoiul to those vibra- tions, and, when moiniied upon a proper sounding-board, gave them out to the atniosjjhere, which conveyed them to the ear of the listener. Now, if the form of vibration in this sounding-board could have been made to coincide in all respects witli that of the membrane at the station from which the vibrations had been transmitted, Reiss would have had a jierfeet .sound telegrajdi or telephone. But this was fur from being the case. The pitch and rhythm of the sounds were perfectly preserved ; their loud- ness or intensity, also, to a very small extent; but the quality was entirely lost. It is notdiflicult to understand the reason of this. Kvery vibration of the membrane caused a pulsation of electricity to traver.sc the wire and act upon the electro-magnet, but as each and every vibration of the armature was produced by a current of jn'ci-isely the same strength, the oidy difference in the amplitude of these vibrations would be that due to the more complete magnetization or demagnetization of the electro- magnet, when the time allowed for the jjrocess was increa.sed by ihe greater ^ilay of the circuit-closer, under the inlluenc(^ of stronger vibrations at tin; transmitting station. The form of the vibrations was of course altogether lost. Any simple musical lone, consisting of a regular succession of uniform vil)i'ations, or any series of sucii tones, could, however, be reproduced with the greatest accuracy. The next important stej) in tin; ]irogre.ss of invention was 252 THE SPEAKING TKLEPHONE. obviously the discovery of some means whereby the proper amplitude of each vibration, or succession of vibrations, either sim2)le or compound, could ])0 directly reproduced by means of the electric current ; and when this was once done, the general problem of harmonii; telegraphy niiiy be said to have been solved. This having been accomplished, it was not difficult to foresee that two important practical applications might bo expected to follow, namely, multij)lo transmission, and vocal transmission. I believe that this discovery of the true method of transmitting oom]iosite vibrations was first publicly announced in the Journal of this society, 1 in a paper contributed by Mr. Elisha Gray, it having been made by him in December, 1874. It consists in causing the ett'ective strength of the electric current, by which the transmission is efTceted, to rise and fall with the varying amplitude of the vibrations or waves whicli are to be reproduced. Nothing could be more simple and beautiful in a th(>oretical point of view, but the practical exemplirication of the method, as is usual in such cases, presented considerable difficulty. At the time of making this important improvement, Mr. Gray had already been engaged for more than a year in endeavoring to devi.se a ])ractical means of transmitting and simultaneously reproducing a number of tones, so as to utilize them for the jiurpose of multiple tclegra})hy. Let us briefly glance at what he liad already accomplished. It was observed in 1837, by Dr. Page.^ that a musical sound was produ('e(l by a magnet, between the poles of which a Hat .spiral was ])laced. The S(Mind was heard whenever contact was made or broken between the coil and the batti'iy. These obser- vations were confirmed and extended by De la Rive, Wert- heiin* and many others. The a])paratus employed by these 1 Gray, Journal of Amfriean Mectrieal Society, vol. i., p. la. Tliis uppnratiis and its inoilij of operation will bo t'ouinl iIcsitUh'iI in di'tail in (Iniy's patcntK, No. 1,874, of .May 4, Is^ii (Gruat Britain), ami lsil,:!4o, of .lannary li'., 1S77 (United States^ " Vugti -American Journal oj ,Scieiive (first series), vol. .\.\xii., p. 369; ibid., vol. ixxiii., p. 3r.4. " Do la Kive — " Traits li' Eleelricit^.thi'nrique ef a/)//?iyW'-'," 'T'-'itf'"*'' Translation, by V. ('.Walker, vn], i., ji. 30U; ; alxo, " Kniglit'x .VIoehanieal Uiotionary," Arti- culating' '' Telephone."' * Ilii.l.. vol. i., p. ;!or. SOUNDS PRODUCED BY MOLECULAR CHANGES. 253 experimenters ruiiy Le described in general terms as an electro- magnet with a self-interrupting break-piece attached to its arnia. tnre, and another magnet in the same circuit for producing the sounds. The sounds proceed from the core of the magnet itself, and arc caused by the molecular change which takes place in the iron at the moment of magnetization or demagnetization. When the current is interrupted a sufficient number of times jjcr second, the successive sounds prod.uce ujion the ear the effect of a musical note. The method by whicii (Iray at first sought to accomplish the desired result of multiple transmission was by arranging two or more self-interrupting magnets, adjusted to different rates of vibration, so as to close the circuit of the same line at the sending station, wliile at the receiving sliition all thi^ currents passed through a series of electro-magnets, equal in number to the transmitters, and having armatures severally adjusted to their respective rates of vibration. As Mr. (iray has already descrilied this apparatus at lengtli in a preceding numljer of the Journal, 1 I need not enter into further particulars con- cerning its construction and arrangement, but will in a few words jioiut out the reason why it failed to answer its intended purpose, e.\ce2)t to a very limited extent Suppose we have two self-interrupting transmitters, one of which, a, makes six vibra- tions in the same time that the other one, b, maiccs five. If we now set them in op ration, first one and th(Mi the other, and record the pulsations on chemical ]}aper at the receiving station, we should obtain the results sliown in fig. 121 atrt and b. But if both are set in operation simultaneously, wo get tlie result sliown in the third line of the figure, at c. Now, it is obviously (piitc possible, by ins'.iriug a proper relation between the times of vibration of two or even more transmitters, to avoiil any material interference bctwi^en the different sets of pvdsations, but a limit is very quickly reached, because, as you will readily perceive, ' Gray — Tnurnnl .imiriran fClecfrirdl finrittij, vol. i, pp. 5, li. For detiiils iiiul fiirtliiT lU'scriptiou srn spoi'itiwitions oC Gniy'.s ]mtiMits, viz., 'J,ii4ii, of .Inly 'JH, l'*7t, uiiil V~\, ot'Mari'li lii, InT.') ((Iroiit Hritaiu) ; also No. li!ii,iMt.-), ot' July 'JT, l^T.') (trnited StuteH) ; also, "Knight's Mechanioal Dictionary, "' .\rtii.'iiliitin)^ "Telephone." 254 THE SI'KAKlXration, the normal rate of each armature bar dillering from that of the other. P^ach arniatiu'e bar will i-espoiid to its corresponding set of vibrations on!}-, and it makes no difl'ereiiee wiiatever whetiier these vibra- tions are transmitted alone, or \vh(>tlu'r they form a constituent part of a compdsite series of vibrations. Eacli set (jf vibrations is broken up into dots and dashes by the action of a key, just as if it was an ordinary continuous current. But as a matter of fact, the main circuit is never broken, although the stnuigth of the current is constantly varied. The manner in which these armatures are thrown into vibration by tlie properly timed impulses of the electric ciuTcnt acting upim the electro-magnet is, as you will readily jierceive, strictly analogous to that of the swing, which can oidy be set in action liy properly timed impulses; or that of tiie tuning fork, sot in vil)ration by the tiny blows of the little atmospheric waves, in the manner which has already been e.x plained. Tlie re|)roduction of articulate vocal soumls at a distance. , belong to the class of sustained tones which can be used in nnisic, while the character of conso- luints mainly depends upon brief and transient noises. The 1 lleliiilmltz .PiV I.fhre. von ilem Tnnempjinduntjtn (Ellis" Tr;iiislation\ Clmp. IlL 256 THE SPEAKING TELEPHONE. pro])lem in this onso wiis to rcproflnco at tlio reooivinp; station prei;iscly the same vibrations in the atmosphere as tliose pro- duced by the voiee of the speaker at the transmitting station. We have seen why Reiss was unable to accomplish this. Let us see wherein later inventcjrs and discoverers have been more fortunate. Some time prior to February, 1870, Gray conceived tlie idea of attaching to a stretched membrane, such as that used by Rciss, a resistance aiii)aratus, wl I i should ])e placed in a con- stant circuit, and caused to vary with tlie vibratit)ns of the mem- brane in response to the sonorous waves travi'rsing the atmo- sphere and impinging upon it Of course, if this could bctlone, it would bo easy to attach an electro-magnet with an armature formed of a circular i)latc, which would respond to vil)rations of every character, and thus reconvert the waves of electricity into aerial sound waves. A caveat, describing this invention, was fded by Gray in February, 1876, and himself and others have since been engaged in perfecting and elaborating it, with a very satisfactory degree of practical success. ^ We will now turn to the labors of another inventor in the same field, Mr. Alexander Graham Bell. Like Gray, he had been for some time at w^ork upon the problem of multiple tele- gi'aphic transmission by means of harmonic vibrations, and when we consider that each of them appears to have been, at least as late as October, 1874, in entire ignorance of the labors of the other, the singular coincidence in the results which they finally attained was not a little remarkable. Gi'ay had approached the • Since the tibovo wiin written, Mr. Tliornii.s A. Edison, of Menlo Park, New Jersey, i.s said to have obtained very satisfiietory results with a telepliono eon- strueted upon tlie general plan set forth in Gray's eaveat, i. c, a variable resistance controlled by the vibrations of a diaphragm. Edison made the discovery that plumbago possessed the curious property of altering its electrical resistance in pro- portion to the pressure to which it is subjected, and availed himself of this dis- covery in the construction of his telephone. More recently the snmo c.vpcnnicnter is said to have obtained still better results by the use of carbon in the form ol'.lamp- black, from the smoke of an ordinary liydrocarbon lump, compressed into- u eylm- dricul button. No details of tluH apporutus Lave yet been made public. whicli HELLS KXPRIUMENTS. 257 sul)jcct from tlic stiiiul-poiiilof ;ui clcctriciati. Tu'll, on tlio other liiind, was a pliysiolou^ist, ami so a|i|'r(iarluMl it, from tlio o[)posito (lirectionj if I may iisd liio cxin-i'ssioii. As early a^ 18(17, lie bocaino iiitcre'stcd in tlio rcsrarrlu'S of llclmliolt/,, iM'caiiso of their beariii<^ upon tlio siibjci't of liis professional stiily, voeal physiology, or, in other words, the mechanism of human sj)eech. Ilia earliest experiments appear 1o have been made in Buslnn in 1872, but were f^ubstantially re[)etilions of those idrcady made by irelmholtz. In November, 187;i, ho eomplete(l an ex|)eri- mental instrument witli two self-interrupting transmitting reeds, and two corresponding receiving reeds, the transmittcMS being connected in multiple are, exactly as in Gray's first metliocL For reasons whieli have alnnidybeen given in speaking of Gi,. 's apparatus, it is jiossible to transmit two separate .series of vibra- tions without material intcrferenci; in ihi- manner, yet a limit is very soon reached, because the current beeomi>s practically con- tinuous. Bell continued his experiments in multiphi trans- niissiuu during the years 187-i: and 1875, but it does not ap])ear that anything of practical inip(U'taneo in that direction n'snlted from them. At length ho .seems to have turned his attention to tho development of the speaking telephone, ami in the spring of 1876 he arrived at some important results. In a communica- tion presented to tho American Academy of Arts and Sciences, May 10, 167(5, and publislied in tho proceedings of the soriety,^ Mr. Bell gives a .somewhat detaih^d account of his rescjarches in telegraphy up to that date. I quote from this ])aper the follow- ing description of an e\i)eriment in vocal transmission, prob.a,bly the first one in any degree successful, which a[i[icars to have been made by liim early in the spring of 187G, and is of great interest : "Two single-pole electro-magnets, each having a j'csistancii of ten ohms, were arranged upon a circuit with a battery of live carlion elements. The total resistance of the circuit, exclusive 1 Si'o paper ri'ad by I'rof. Bull bef'oru tlio Sdc. of Tol. Eiijjineors, nn abstmot of wlik'li may lio fuuiul in tlio Tcl«jrapliic Journal, Vol. V., ji. i!T'i. ' Bell — I^ooeedings of American, Academy of Arts and Sciences, A'ol. XII., p. 1. 268 TJIK Sl'KAKINO TKLEPIiONK. of the l)att(My, was alxnit twcnt y-fivo olimA ] )nini-lica(l.'^ of jrold- bcatei's' t^kiii, seven ct'iitiineliv.s in diaiiictcM", -wcro ])lace(l in front of earh I'leelro-nKignet, and a circnlar ]iieco of cl()ck-siiriii;.r, ono centinietro in diameter, was glnecl to tlio middle of cadi mem- brane. Ti:o telejiliones, t«) coiistrneted, wcro placed in different rooms. One was retained in the cxp(>rimental room ami the other takf-n to the basement of an adjoining honso. Upon .sing- ing into the telej)honc, the tonesof the voice wcro reprodnced by the in.rs fi'om that of Gray, inasmuch as the latter varies tlie resistance in tho circuit without changing the cleetromotivo force, while Bell varied tho electromotive force, the resistance remaining constant, Tho bat- tl a( lh en tilt 1 Ibid., Vul. XII. !'• SiMi, iiLsc), Teleiirnpk ,h>ufiial^ vi^I. V,, p. '.'77. Al'I'I.lCATlo.V Ol- I'KHMANKXT MAGNKT.S. 259 tcry cniTcnt f-'Tvod no dtlicr purjiosc, in BcH's cx|ieniiioiit, tlian to lu'i'iiiiuiciilly iiii'.giu'ti/o llio .siil't ii'iiii cnics oC tlio cleclni- magiu't, wliilo till! niiigncto-ii id net ivo waves wcro superposed. In Septcmlier, 1876, Prof. A. J']. Dolliear sulwtitutod ii, jicrnianent steel magnet for tlio ehictro-maLriietic arrang(>iiient ]ii'eviously employed hy I'x'll,^ ami tlio instriiiiieiit thus improved is now going into very extensive us(\ Its jirlieiihition, wliilo distinct, is not very loud, altliougU sudiciently {t when thrust into or withdrawn from a hollow bo!)bin. This was di'signeil to move a needle. Also [)i\)posed to 1 Alislr.'ii't fruiii " Ufsc'iirulics in Tclcplioiiy," liy I'rot'cssor A. E. Bolbeiir, nf TulU CoUujje. ]>OI.BEAKS TKLErilONlO KErfKAHClIES. 281 have a like instrument at the receiving station, whieh I pupposed would duplicate tlic movements of the lirst instrument. The receiving magnet was to be furnished wilU a ])en, and thus regis- ter the movements of the transmitting one. I saw that the move- ments of the sc(!ond would of necessity be precisely like those of the first, but did not at that time know that the movement of the second would be so feeble as it actually is. I triced to interest a number of persons in this invention, but did not succeed. As I had no mcians, and was working my way through college, T was compelled to abandon the projcict. It will be seen that the ])rin- ciple of the present S])caking telephone is es.scnt!ally involved in this invention of 1864. 18G7. — Invented u gyroscope to run by electro-magnetism, and which demonstrates the rotation of the earth. This was whih; I was a student in Michigan University. This inacliine, con- strucLcd by Ritcliie, was exhibited at the Centennial Exhibition. 18()8. — Conducted a series of experiments to determine the quantity of matter transfcnvd by the ek'^tric spark. The ])]iu\ carried out was as follows : One thou.sand inch sparks from an electrical machine wi-re rect-ivcd into chemically pure hydro- chloric acid from a ball of coj)pcr. Tlu> liquid was made blue by the addition of ammonia, and thencompared with a standard solution which was reiluced until the colnrs of the two were juilged to be alike. That gave ajiiirDximatcly tlit; transferred co]i})cr for that numlx'r of sparks. The same jilan was tried with iron, silver, l(>ad ami some other substances, using, of course, dilTercnt reagents with ciicl!. ' 1870. — Discovered that the so-called magnetic ])hantoiu was permanently magnetic; that it would jr class (h.'monstration. 1873. — Made some large tuning forks for proj\'cting sound- curves u]ion a screen; also discovered a method of very mueh amplifying thesi! viliratioiis.^ A ])air of these forks was ex- hibited at the Philadelphia Exposition. At the same time in- \ented an attachment to the whirling-table, for accomplishing the same thing.2 Discovered convertihility of sound-vibrations into electricity. Using a tuning fork in eonneetion with a thermo-[iile and gal- vauometei', 1 noticed that when tlie fork vil>rated the needle wa.s deilected. Further observeu tlie ed'ect of a vibrating tuning fork, which was also a ma;^iiet. u|)ou the current from a tlierm()-])ile. At the ]'ortland meeting of the American Association, in 1873, read a short ])a|ier in regard to tiie lirst of these experi- ments, wiiich 1 thought was new; but said notliing about the. second, as 1 cousidci'cil it was only a ])arlieular easi; of magneto- curr 'uts, which wen- well known. JN'everthelcss, it was pre- cisely the sanu! thing as tlii' uiidulafory current which I'roiessur Bell claims to h;ivc invented or discovered. While engaged in making a manometrie flame capsule, T in- vented the o|ieidosco[ie. •' 1 also ])roved that the; shee't of air issuing from a sounding 1 Sci' .Intininl (if h'riDiliiii fiin/itutf, 1^"'!. ' See prncri-ililltrs iif .Vnic-ririlll AsMii-illtioU, l-ST'!. " t>uo Joitrual of Fraii,klin /lutUiUe, liIU. Ai'i'i'iidix I. DOLBKAK S MAGNETO-ELECTRIC TELEPHONE. 263 1 orpran-pipo vibrates like ;i reed. This was done by filling nn oruaii licllnws with smoke, and examining it through a slrobo- .rations ujion tin; paper, and con- eluded to construct the telephone vilirating armaturi> entirt'ly of iron, in the form of a comjilete plate fastened at the edges, insti'ad of I icing attached to a membrane as before. 1 mi'asui'cd the distance through whii'li I could get a signal with such a (tui'rent. J siu'ceeded in doing so through a n'sist- anee of fifteen thousand ohms, J now thought of obtaining a ])atent upon the sjieaking tele- phone with iicnauncnt magnets, and began constructing suitable 264 THE SPEAKING TELEPHONE. instruments to servo as ;i ]iatpnt model, but before these instru- ments were eompictcil, I was inlormeil that Professor A. Graham Bell hail declared tliat ho liad secured a patent up(ju the same thing two or three years l)efore. On tlie 12th of Fcliniarv. 1877, Professor Bell gave a lecture and exhibition, at Salem, Mass. AVithiii a day or two I called upon him to see liis fi.\tures. lie was not in, but his assistant, Mr. Watson, showed them to me. They were substantially like mine. I invited Messrs. Watson and Bell to come to College Ilill and sec my apparatu.s. Fi'j. 122. Fl(j. 123. Mr. Watson said I'rofe.ssor Bell wished to know what the resistance of the human body was, and asked if I could measure it. I promised to do so, and in a few days sent him the meas- urement of the resistance of the bodies of about twelve students, for whiih ! re('(>ived a letter of thank.s. About the first of ^larch. lo77, 1 chanced to see tlu? ollicial gazette of the I'atcnt Ollice, containing J'rofessor B'll's ]iatent of January 30th. I.s77, and found that I had been deceived in regard to his having ]iatented tlie application of permanent mag- n(!ts to tlie telephone prcsioiis to my iiiventimi. and acenrdiunlv went to con.sult ;i lawy^'r about it. I was considerably dis- couraged on aci'ount of his statement of the ])robable cost of an attempt to secure my ritzht.-:. 1 trifid to interest several ]ier- sons in mvcase, but without success. DOLBEAR ASSERTS HIS RIGUTP 2r,5 About tlie lirst of ^May Profossoi' IJell lectured in Boston, and jmblicly declared himself to ])« without a comiK'titor. I at onco challenged his statement, iiifor .liiig liim what I had done; yet ho (continued to riMterale his statement in all his subsequent lectures. In July he wrote to me that, as ho was acknowledged that I had •uvented the j'lephone indepcnch-ntly of himself. In 1877, I was enabled to make further investigation into the e mlitions necessary for the telegraphic transmission of speech, and have tl)e following di.-^coverics and inventions to report as the result of those investigations: A eu.shion for the vibrating diajihragm, by which greater amplitude of viliration is ohtained. with increased .sonorou.s etlects. Telephones maiie in this way have l)een heard one hundr(>d and lifty feet away. The uda])tation of the common string telephone (lovers' tele- 266 TUK Sl'KAKIXd TKLKI'HONE. jri'apli) to a Morse souihV-M' or rclav, liy wliiHi s|u>ecli iiiiiy be traiisniitlnl, the same iustnimcnt acting' cither a^ receiver or traiisiiiitler. That the streiigtli of tlie souml is much more dciieiulont ii]»on the strength of tlu' magnets unci si/e f)f iho [ilate than upuu tlu; diameter of the wire and immher of turns upon the ])ol)hin. Some of the loudest tones liave been obtained witli bobbins eon- taiuiug but two or three ohms of number 2b wire. Foj. 125. Thar c .'^njtnnnd inagu(>ts are mui'h b"itrr in every respect than singe magnets, and li'e compound L' magnet is the licsf of all forms which have l)een tried. The tuning fork call. The devil's fiddle call. Tlie 1)ell call — falling harmonic bell. Tlie paper diajiiiragm. with elcctrd-magnet armature. Sec fig. 124. The liattery telephone, in winch plates of t ,vo dUrcrcnt, metals TlIK ,Sl'KAKl.\(r KLKl'Tlilil'irONK. 267 aro pc'pnrntod hv a iion-coTidnctnr in such u way as to make a shiillow cell. \Vlioii ii sDi.nd is iiia(](^ a.ira'mst one of thesi', as al .1. lig-. 125, tliij curriMit i'-oiii the crll is Invil^cn \\[) into waves lircciscly like tlic iiKiveiiuiits of tlic sound waves, and speech is rendered remarkably dis:inel from the emi^loyment of such a sounder. The cleetroiihonc or moditieil Reiss telephone (lig. 126). In thisinslniment a i-ingeinlate, and talking or singing be resumed, tlie articulation becomes remarkably good, though the sound is not very loud. Tf a strong battery of iifty cells, or more, l)e put in circuit, and the screw be turned down so as to have a jiunping spark between the point and the plate, the viVirations of the latter intro- duce a variable resistance in the air. If at the same time there is a strong current, the result will be very loud talking. Indeed, it Avil! 1)0 hjudcr at the receiving than at the sending station. This has been used over the lines between Boston and Kcw York, and between Mdford, New Hampshire and Boston. In each case, every person in the room could hear the talking from the other end of the line. In this device it is found best not to use a very sharp point, but one having a surface like a sewing needle, with aljout one eighth of an inch broken off from the point. Such a one gives much better results than a sharp point, for th(! ol)\-ious reason that a greater (piantity of electricity can pass from such a surface than from a line point Tf electricity of high tension, like that from ar ordinary electrical machine, be used instead of the current from a battery, the result is the saine ; talking is j'ossiblc, the articulation is good, but the tones arc not so loud. Large plate for a call. If the plate be made a foot or more in diameter, but mounted near the middle concentrically, the magnets and bobbins being the same as usual in sixc and strength, tlie jilate may I)e struck with a billet of wood, or other material, and the thump will be very loud, as heard from an oi'dinarv tcle])lione; in fact, loud enough to be heard fifty feet away. It is also good as a receiver call. ]>01iUKAU.S I'JtdJKrnO.V AI'I'AHATUS. 269 AX ATTAHirMKNT To TIIK WHIRMNCr 'I'AHI.K FOR PKi > ) ECTING I.ISSAJOU'S CrUVKS. ^ The costliness of the u.sual ainmratus for tlio projection of Lissajoii's curves lias led me to devise a method for a(!eom]iiish- inu- tJie same results in a comparatively inexpeiisiv(! way, \vhi(;ii proves in other ways to hesujterior to tln^ metliod with viln'ating f < )rks. It consists of the followinLC attachment to tiie whirliuLC table: Fi'j. 127. Two posts, 2^ <'""^ t>'' i'i"G made fast to tin' frame upon the opposite sides of the inci'tiu phile a. A small wooden j>idley, s. {[vx. 127) about an inch in diameti^', is made to turn upon an axis that is made fast in tlu; jiost^), and witii such adjustment that the pulley rests upMU the plate ^, ill ils lower iMid, wliicli is npposilc tlii" face of tlu! pulley 5 (lij;. 128). Auotiicr twist ill tlu; win- ;tl ') will bn iicciicd, for :i ]iin wliicli is fast in tho post p. Tiiis will make a lever of the wire /, with \\u'. fulcrum at o, and if it is i)roporlv fasteneii to the hiuj;jofif the uiirror, will cause it to vibrate in a hori;5oiital plane when tlie phite a nn'olves. A somewhat similar arranL^cmeiit is made for the other side, save that tin; friction pullev s' lias it3 bearing made fast, in a separate piece c, which is so fasten(>d to the end of a loiit; screw <', that till! wliohi lixtiire can l)e mo\-ed to or from the centre of the ]ilate ct. The piece c is fiirnisheil with two j^fiiides, which keep it steady in any ])Ia(\e where it is )mt. The mirror m \a made to tilt ill a perpendicular })Umo by an arrangement it. Tf moved half wav, it will make one revolution while the other makes two, jind the vibrations stand in the ratio 1 : 2, represented by forks in octave. Such ratio is shown np(jn the screen by a form very much like the figui'c 8, and known as the lemni.scate. Between the.so two jilaces, every musical ratio in the octave can be got, and the resultant motion.^ ])rojected in their proper curves. More than that, while the mirrors are both vibrating, any of the ratios desinnl can be moved to at once by merely turning the thund) screw d, which is wholly impos.siblo with any forks, which reipi.ire .-toppage and adjustment of lugs for each different curve. Again, if the i. ::tnrG c is moved .still farther toward the centre than half \\ r.\ tie curves projectdl will be those belonging to the pc^'oml ociave, until the )iullcy I't.'aches three foui'ths of the way, when the ratio will be 1 : 4, and the resultant figure will be like a much flattened double eight. If one would show the phenomenon of beats, it will be ncces- IMAGE EVALUATION TEST TARGET (MT-3) Y A {/ ^ J^4i. V- u. ^ s 10 I I.I 11.25 lU 1.8 1.4 11.6 Pm ^^ ^l^^ %''" "^/^i '/ photographic Sdences Corporation 23 WEST MAIN STREET WEBSTER, N.Y. 145C0 ,716) 872-4503 j9 \ iV 4!> 272 THE SPEAKING TELEPHONE. sary to have tlie mirror m and its attachment so adjusted as to have it vibrate in a perpendicuUir plane like m'. This can be done by fixing its hinge at right angles, and the rest the same as foi mirror m'. The reflected beam from the second mirror may be received upon a large mirror held in the hands, and thence reflected upon the wall or screen. All the phenomena of vibrations that can be shown by foi-ks can be reproduced on a scale that is not approached by means of them, by any one possessing a turning table, and at less than the fifth of their cost ON THE CONVERTIBILITY OF SOUND INTO ELECTUICITY. ^ I have found by experiment that if a vibrating tuning fork have its sti.'m ajiplied to the face of a thermo-electric ])ile wliich is in circuit with a delicate galvanometer, the needle will be dc- fiected, showing that electricity has Ix'cn develo})cd in the pile. The question is as to its immediate origin. It may be assorted that the vibrations of the fork arc competent to develop heat, which, in its turn, is converted inio electricity, so that its appear- ance is a secondary phenomenon. To this explanation counte- nance is given by the exjiei-iment of Professor Henry, who found that the deadening effect of a rubber cushion, when the stem of a vibrating fork was: put upon it, was due to the fact that tluM-ibra- tions were converted into lieat. But the vibrations ai'o not no- ticeably deadened in the former case, and the junction of the metals is subject to definite and measurable vibrations. The antecedent to the production of electricity is the contact, either mediate or immediate, of substances, wliieh dilfer ineompo- sition or in condition, and if electricity is a mode of motion, it ought to appear whenever .1 motion may be set up at such point of contact as mutually to disturb the molecules of the differently constituted matter. That the vibrations of the fork are compe- tent to do this without necessarily giving rise to the phenomenon 1 By A. E. Dolbeur, of Botliiiiiy, W. \n. From tlio I'rocccdiiijrs of tlio Amuricau Associatiou for tho Advaucomuiit uf Sc'iuuue. I'ortluud iiiuutiii);, Aui;u.st, \>i1'i. CONVEKTlBILIXy OF Soi'Nli INTO ELKCTRICITY. 273 of heat, may fairly l)c inferred, I tliink ; so that, a priori, one should look for electric! phenomena from such a >mbination of favorable conditions. At any rate, it will hardly he asserted by any one that because tlu; electricity is gi'iieratcd in the thermo-pile its im- mediate cause must be heat. 1 do not know that it has ever been ])rovcd that heat motion was theoidy kind of motion that was caj^able of direct conversion into electricity in. the so-called thcrmo-pair. It is probal)le that the more general statement is true, namely, that molecular disturbance at the junction of dis- similar metals will give rise to electricity. We know that the niole<-ular disturbance called heat will give rise to It, and it is not improlcible that the disturbance caused by a regularly vibrating tuning fork, may do thesamo thing directly. My exi)eriment does not prove that such is the case, but it hints at it, and I olTcr these considerations to meet the objections of some who take it for granted that it cannot be true that sound viVjrations arc, really converted into electricity, except in an in- direct way. This is ea[iable of verification, I do not doubt, but I have not had time to apply the experimcntum crucis, as the idea did not occur to me until a day or two ago, and I bring it to the association as an interesting experiment, whatever its ratioaale may be. CHAPTER IX. litPKOVEMEXTS OK CII.VXXIXG, BLAKK AND OrHERS. In the winter and spring of 1877 a notable series of experiments were made b v a few soientilic gentlemen in Providence, R I. , which resulted in making tlie teleplione portal)le, and in giving to it distinct articulation. ICvery step loading to these important results was communicated to Prof. B(>11, and the principal im- provements thus originating, especially the handle instrument and the mouth-jiicco, were at once adopted by him, and form j)art of what is now commonly known as the handle telephone. In March, 1877, the speaking telephone, in its most practical form, consisted of a box resembling a photographer's camera, with a two inch tube for mouth-piece, opening into a cavernous air chamber in front of a plate of sheet iron about 4J inches in diameter. Behind this plate was a large TJ magnet, with a soft iron core clamjied to each pole, surrounded with a spool of fine insulated wire. These instruments were unwieldy, and their articulation defective, for three reasons : First, the mouth-piece did not converge the air on the centre of the plat- and the cavernous air chamber produced reverberation; second, the magnet s of the U magnet reacted with the parts of the plate which were opposite to them on each side of the centre; third, the plate was too large and heavy to respond perfectly and promptly to the average voice. Experiments, eonuncncing in the physical laboratory of Brown University, and continued several months by Prof. Eli W. Blake, Prof. John Peirce, and others, culminated, in April, in tlie con- struction, by Dr. William F. Channing, of tiui iirst portable telephone. This consisted of two small blocks of wciod fastened to each other at right angles — one perforated for the mouth-piece and holding a ferrotype plate, 2^ inches in diameter ; the other IMPROVEMENTS UV PROVIDENCE EXPERIMENTEHS. 275 sup])ortinff a c'nin])ouii(l U inagnet (mado of two three; incli toy inaguots) witli a .single soft iron core, carrying a spool of iine insu- lated wire, clamped to one of its ])oles and opposed to the centre of the ferrotype j)late. The other ])olc of the compound magnet was either brought in contact with the outer edge of the plate or left free. This little instrument, weighing about twelve ounces and easily held in tlic hand, especially when mounted on a handle, talked more distinctly than the large in.strumcnts, cvcmi over long circuits, thougli not quite so loud. It was followed later in April by a telephone made by Prof. Peircc, in which a small (iompound (J magnet was enclosed in a cubical block of wood, on the top of wliieh he placed for the finst time his converging mouth-piece — an acoustic apparatus which deserves .sjjccial de- scription. Fig. 129. This is .shown in .section in fig. 129. The sound waves con- verge u[)on the centre of the plate through the aperture a, usually about j'jj^ inch diameter. The sound waves also spread symmetrically from the centre, and act upon the plate through the very flat air chamber b b. To prevent resonance and ensure the prompt response of the plate, this air chamber is u.sually made only from ^ to j\ inch in depth, and about If inches in diameter when a ferrotype plate (c c) is used. This mouth-piece made distinct and natural the previously obscure articulation of the telephone. At the time i'rof. Peiree's mouth-piece was made. Prof. Bell liad arrived at the disctovery that the instruments talked better if the air chamber, usually made deeper than that shown in fig. 53, was stulTed with paper. The reason will be sufficiently obvious from the above. 276 TJIK Sl'EAKING TEI-Kl'HoyK. Prof. Peirce'ri npriglit block ^vas followed niitiirally by tlie "liamilc teleplioiio," now in general use, whicli was made l)y Dr. Clianning early in ^[ay, 1877. Figs. 1?,(^ and 131 slioi'.'- both a sec- tional and penspcctive view of the instrument. In this a small straight magnet, simple or compound, carrying a single soft iron core and spool, is enclosed in a light and elegant handle, and the Mg. 130. ferrotyjie plate is mounted in the circular head, of which the moutli-piece forms part. Tlie design and .stylo of the instrument is due to Mr. Edson S. Jones, another of the Providence experi- menters. ' . After a competitive test with the box telephones, as at that time made, tlie handle telephone was adop.ed and sent out early fiy. m. in June by the Telephone Company ; and its portability, ele- gance and superior articulation contributed largely to the ra])id diffusion of the telephone in this country and in Europe which immediately followed. Prof. Bell was familiar with the preceding Providence experi- ments which had already made tlie telephone portable, and m P hi In nil sh. cir lill'KOVEMENTS liY I'UOVIDEXCK EXl'ElU.MENTEUri. 277 which suggested tlic liandle form. In May, shortly after the construction of tlie handle instrument in Providence, and before it reached Boston, Prof. Bell, working in the same direction, had put a U magnet, each pole armed witli a core and a spool, inside of a handle. The instrument was too cumbrous and i lelegant f^r adopjon, as well as defective in construetion. j'rof. Bell's desire to put both poles of the magnet to visible use was especially unfortunate in this case, as tlie smallness of the plates in the portable telepliones makes it impossible that the two poles of the? TT magnet should act anywhere near the centre of the plate. Tlie instrument was not adopted, and it could not have accomplished for the diffusion and commercial success of the telephone what was done by the original handle instrument. Y"et, with no other basis than this experiment. Prof. ]5ell. in his lecture in London, before the Society of Telegraph En- gineers {tice page 7t)), says : " Two or three (hiys after I had con- structed a telephone of the portable form, containing the magnet inside the handle. Dr. Channing was kind enough to send me a pair of telephones of a similar pattern, which liad l)een invented i)y the Providence exj)erimenters." As already stated, the in- strument thus referred to is an accurate representation of tlie handle telephone of Dr. Channing and Mr. Jones, which lias had so wide a career, and dill'(M-s bi-oadly in typo from the experi- mental instrument of I'rof. Bell, which never jm-ssed into nsc. Prof. Bell, in the above extract, not only claims the origination of the handle telephone, which has gone round the world and has a recognized place in the history of speaking tck^phony, but he also implies that he gave to the ti'lc]ilione jmrtable form, thus ignoring one of the 2)rincii)al contributions of the Provi- den ■'! cxpei'imenters. It happencil with the telephone as with the ]\[orse telegraph. In the l)e<'inning it was supposed that the power of the instru- ments was proportioneil to their size. Later experiments have shown in V>oth tliat more ilelicatc instruments are tiie most clleeti ve. 278 TIIK Sl'EAKINa TKLKPHONE. It will 1)0 ol)scrv('il that Professor Bell is criticised liorc, not for cl;iiiiiing that ho had made a straight magnet tck'phonc, but for claiming this in comV)inatiou with the handle, and iiguring tiiis combination, which constitutes the well known handle iu- strameiit, as his own. His real claim is to the independent experiment of jJUtting a U magnet in a handle, subse(pient to the construction of the genuine handle instrument in Providence. Another ])i-aetical result obtained in Providence as early as June, was tlie glass plate tel(>plione of ]Ienry W. Vaughan, State assayer. A disk < t soft iron, about the size and shape of a nickel cent, was ccnientcd with shellac to the centre of .a very thin glass plate, 2^ inches iu diameter. This, with Peircc's mouth- [liece and the usual magiu'ts, gave the loudest and clear- est articulation attained at that or at a later tini(>, and may be the germ of important improvements. Mr. Yaughan also nuide, before the tele]ilionc had been soen in Fir.nce, what has since been described as the midtiple tLlephone of M. Trouve. In this telephone, plates form the sides and ends of a cubical or i)oly- hedral chamber, a magnet and coil being behind each i^hite. Among other scientific observations with the telephone, Prof. Pcirco heard the auroral Sfuind.s early in the summer of 1877, and Dr. Chaiming noticed the characteristic telephonic .sound of lightning, even when distant, ])rcceding the visible flash. Prof. E. W. Blako mailo the capitid experiment, im])erfectly reported in Prof. Bell's lecture, of substituting a soft iron bar for the nuignet of the telephone. Whenever this bar was turned iu the direction of the di])]nng needle, the telephone would talk by the earth's magnetism; but when swung up into a position at right angles with the dipping needle, the telephone became ])erfectly silent Prof. Blake also talked with a friend by telephone for a short distance, using the parallel rails of the san\e railroa!" eiicli. Tlir wires licing eonnected, if one. tuniiii.' fork is struck tlie otiifi- responds at a distance. Tlie iiiimes of Messi"s. Jiouis W. Clarke and Charles E. Austin should he mentioned among tlie corps of Providence experi- menters as contrihiitors to this cha[)tiT of telephonii; progi'css. 1 With the ohjeet of stimulating inqtiiry into the means of improving the telephone, which is the most beautiful adaptation Fig. 132. of telegraphy ever made, I desire to draw attention t«i a few sim])le methods by which any one may satisfy himself of its ])raeticahility ; for no one having witnessed its performance can fail to sec a great future before it The recorder of Sir W. Thomson, shown ii\ fig. 132, affords a ready means of speaking, and gives out such clear tones as to make the listener at first involuntarily look behind the instru- ment for the speaker (who may be miles away). It sulficcs to 1 Juliu Gott. Journal Society TeUgraph Engineers. No8. XV. und XVI. 1S77. 280 THE Sl'EAKING TELKPIIOXE. take a tube two iiiclios in diameter, and stretch over one end a membrane of parcliment or tiiin gutta pcrelia (tlie latter is less allec'ted by the breath, the former becoming somewhat flaccid after a time). To the centre of the membrane cement a straw, and fix the tube in front of the instrument, about six inches from the movable coil li ; cement the otlu-r <,'nd of the straw to the coil at the point where the silk fibre k is usually fixed. This is all that is necessary for both speaking and receiving. Six or eight cells of battery connected in circuit with the electro-mag- nets sullice. A pair of these tubes may also be connected in a similar nuinner with the tongues of two polarized relays. The tube is to be fixed in a convenient ])osition, at right angles to the tongue, and the free end of the straw cemented to the tongue, taking care that the latter is free fmm its ordinary contact points. No battery is required for sjjcaking with this arrange- ment. Or a pair of these speaking tubes may be connected with the ordinary armatures of any instrument or relay, and a curi'ent kept on the line. The armature should, however, not be too heavy, and should be carefully adjusted. The best adjustment gives the loudest sound. In sending, be c/ivful that the arma- ture in vibrating does not touch the cores ot the electro-magnet. A plate of thin iron, such as is used for stove pipes, fixed to an ujiright board, the hitter hollowed out on the side on which the ])late is fastened, and a hole made in the board in front for inserting ji eonvenient tube for speaking, may be used as an armature, and a pair of coils placed in front of the iron plate through which a current from a battciy is flowing, the cores to be adjusted as close as possible; to the plate; this answers for .sending and rci'civing. The battery need not be strong; if it be so, the armatures have to be removed further away from the coils. On a short line the resistance of tlie coils, with a suitable battery, is of little imj)ortance. I have sjjoken as well with small coils of three ohms as with 400 ohms. If a pair of coils at the receiving end be placed on a violin, and connected to the line on which there is a permanent current nEMAUKAHLE TELEPnoXK* TIIENOMENA. 281 nnd a scTnling instrument as described, singing ar..'i speaking into the tube at tiie distant end can be heard by j).. ,,.ifi; tiic ear to the violin. The elTcct is exalted by hiying a plate of iron on the poles of the clectro-niagnet. By th(;se simple means — and tliey are selected as being within the reach of many — may bi^ demonstrated the possibihty of speaking over miles of telcgrapli line. The sound of the voice in the tube is not that of a whisper, but of a voi(!e at adi.stance; and the nearer you seem to bring the sound the better your adjustment, and vice vcixa I have s])oken through four knots of buried cal)le without .sensible tlimiuution of etl'eet. When the instruments are not well adjusted, some words will come clear when others do not ; and I have found the sentence, Arc you ready ? pronounced deliberately, intelligible when others were not. The object to be sought for is to augment the strength of the variations of current At })re.sent it is limited by the power of the voice to move an armature or coil ; and unless it can be magnilicd by putting in play a reserve of force, as compressed air, etc., improvement cannot go far. The most hopeful Held seems to be the effecting a variation, through a.sensil)lc range of resistance at the sending end, to vary the strength of current in a primary coil by shunting (jr varying the resistance of a battery circuit ; as, for example, a line wire inserted more or less in mercury. REMARKABLE TELEPHONIC rilEKOMENA. i During five evenings in the latter })art of August and first part of Scjitcmber, 1877, jjcrformcrs statit)ncd in the Western LInion building in New York, sang or i)layed into an Edison musical tclephouc, actuated by a powerful battery, and con- 1 Atistnict frniii a ciiiiiiininioatioii f'ruiii Dr. William F. Chaimiiif,', cifl'roviJuncu, II. I., imlili.slit.J77. 282 THE Sl'KAKlNd TELKl'HONK. Ticotcil witli one or iiiori' cilies l)y ii No. 8 gauge wire, with n-tiirii tliroii;,^! tlii' gniuiid. Ill I'nividouct', on the evciiiiijf of tlio first of tliese concerts (August 2.'S). Henry W. Vuugluin, State assiiyer, and the writer, were eonversiiig tliroiigli magneto telephones over usliunt inudo l)y grountling one of tlie Anierieaii District Telegraph wires in two places, aoout a quarter of a mile a[iart, thnnigh suitable resistance coils. At about half ))ast eight o'clock we Avere sur- .sed by hearing singing on the line, at first faint, but afterward becoming distinct and clear. At the same moment, apparently, Clarence KathVxtiie, talking with a frii'iid through telephones over a private line in Albany, was interrupted by the same sounds. Afterward, during that and subsequent concert even- ings, vririous airs were heard, sung by a tenor or soprano voice, or played on the coriicL The origin of these concerts remained a my.sterv for some time in Providence, and the lines were watched for music many evenings. The programmes heard proved to be ]u-ecisely those of the Edison concerts j)crf()rmed in New York, the singei-s being Signor Tagliai)ictro, D. W. McAneeny and Madame Belle Cole. The question how this music pas.scd from the New York and Albany wire to a .shunt of the District wire in Providence, is of .scientific importance. The Edison musical telei)hone consists of an instrument converting sound waves into galvanic waves at the transmitting station, and a diilerent instrument reconverting galvanic into sound waves at the receiving station. The battery used in sending the music from New York to Saratoga con- sisted of 125 carbon cells, with from 1,000 to 3,000 ohms resist- ance interposed between the battery and hue connections in New York. The wire used in these concerts extended from the "Western Union building, corner of Broadway and I)ey Street, through Park Row, Chatham Square, the Bowery and Third Avenue to One Hundred and Thirtieth Street, and thence via the Ilarlein itnilroad to Albany. On the same poles with this Albany wire, for sixteen miles, are supported no less than four wires running UEMAHKAIU.K TKM-M'lKlNIC I'ltKN'OMEXA. 2H-d villi a I tol'rovidoncc, three of tlit'iii l)ciii^ on tlm Puiiio cros^ ariii, ami one of them heiii<^ Huston wire No. bb east, via Jfartford ami I'rovi- (leiiio; a!s(t for eight iiiiU's a lifth wire, Hostoii wire No. 82 east via New LtJiidoii ami J'rovideiiei'. TlK'.-;e wire.x, iiiclmling the Albany wire, have a eonnnon ground eoiniection at New ^'ork, and are strung at the usual distani • . >art, and with the ordinary insulation. At the I'rovidenee end of the H.' , ; ix New York and l}(jston wires, Nos. 55, 32, 2, 5, 27 and 28 i'uA, run into tlu; Western Union building, in eoinpaiiy (on the same pules and braeket.s), for the la.st 975 feet, with an Anuriean Distriet wire. This last runs e.sj)eeially near to wires 55 and 32, whose pro.vimity to the Albany wire in New York has alre.idy been traced idtove. But here is a distiiiet feature. TIk; District wire belongs to an exclusively air circuit of fou" and a half miles, having no ground connection. 'J'he New York ami All)any and New York and Boston wires are, or may be, grounded at both ends. 'JMie Dis- triet circuit referred to in Providence is geograj)hically two circuit;!, but electrically one, both working through a single bat- tery 01 fifteen cells. Mr, Vaughan and myself having District boxes a quarter of a mile apart, on this circuit, made a shunt for telephonic cornnuinication by ground (connection at each house, including several hundred ohms resistance, so as not to impair the galvanic insulation of the line. The telephone talked through this perfectly, and the sounds of aimospheric electricity were heard in remarkable perfection. It will be seen that the music from the Albany wire pas.sed first to two or more 2>arallcl New York, Providence and Boston wires; second, from these to a jiarallel District wire in Provi- dence ; and third, through a shunt of that District circuit before reaching die listeners there. This transfer of electric motion from one wire to another may have taken place by induction, by leakage, or, in the first instance, in New Yt)rk, by a crowded ground conductor. In the transfer in Providence from th(! New York and Boston to the District wii'e, there was no common ground connection, and it is difiicult 28-1: THE SPEAKING TELEPHONE. to suppose that sufficient leakage toolc jilacc on tlie three brackets ami three poles, which were coiuinoii 1o the New York and the local wire, to account for the transfer in Providence. Tlic mag- neto-telephone has also jiroved itself abundantly capable of pick- ing up signals in an adjoining wire by induction ah )ne. Without rejecting wholly, therefore, the other modes of transfer, T sliouhl ascrilie to induction the principal ])art in the transfer of tlie eon- certs from wire to wire between New York and Providence. What ])roportion, then, of the electrical music, set in motion in New Ynrk, could have reached the listeners on the shunt in I'rovidence? Whether induction, leakage, or crowded ground was concerned, will any electrician say that the New York and Pi'ovidencc wires situated as described, could have robbed the All)any wire of (Uie tenth or even one hundrerlth of its electrical force or motion ? When this one tenth or one hundredtli reached Pi'oviilcuco, will any electrician say that the wires from New "^'ork. ill the course of 975 feet, could have given up to the parallel District wire one tenth or one hundredth of their elee- tri<'al wave motion? Lastly, when the District circuit had .secured tliis minute fraction of the original mu.sic bearing electric waves, will auy electi-ician say that the sliunt as described (containing 600 ohms resistance, while the shunted (piarter of a mile of Dis- trict wire contained only 5 ohms resistance) could have diverted one tenth of the electric motion from the District circuit ? The nnisic heard jdainly in Providence did not, therefore, require or use one tru thoiisandtli, hanlly one huii(b(Ml tliou- .siudth, oC the electro-motive force originally imjiarted to the vVlbany wire. This startling conclusion suggests, first, the wonderful delicacy of the magneto-telephone, on which ]ioint I shall vcntun! to enlarge, and .second, the as yet unimagined capacity of electricity to tran.spu.fc sountl. The magneto-telephone is probably the most sensitive of clec- tro.seopes for galv.inie, magneto-electric, and atmospheric or free (•lectricity, and will be usimI extensively in .«cii'nce and the arts, in this capacity. In the French Academy, on the 6th of Novem- SKXSITIVKXEi^rf i)hoiio as, of all known instruments, opcratiiij^ under tlic inilmMice of tlie most feeble electrical currents. Prof. John I'eirce, of Providence, lias ascer- tained that the telephone gives audible signals with considerably less than one hundred tliou.sandth part of tlui current of a ,lc[)lione, but of powerful galvanic currents. The delicate magneto-elcctrio current of the tele]ilione is not generally exposed to eavcsdroi)ping, luiless dif- ferent !-cts of wires actually come in eontacL Prof. Peirce has observed that if one sei'ew-eup of a magneto- telephone is connected with a ground wii'e, in use at the same time for Moi-se operating, the Moi-se signals will be heard in the telephone, although the other s<'rew-cup is disconnected, and there is no circuit. Here the coils of the telephone seem to be momentardy charged by the pa.ssing signals, on the principle of a condenser. A still more .jving illustration of the electro- scopie delicacy of the telephone is this: Prof. E. W. Blake, of Brown University, talked with a friend for some distance along a railroad, using the two lines of rails for the telephonic circuit. At the same time ho heard the operating on the telegraph wires overhead, caught by the rails, jirobably by induction. The aksencc of insulation in this experiment recalls another curious observation. The telephone works better in some states of the atmosphere than in others. A northeast wind appears specially favorable. When a storm is approaching the sounds 286 THE speakinct telephone. arc sometimes weak ; but the tnlking is often lond and excellent in the midst of a storm, wlien insulation is most defective. I have just verified this hy talking over a short line where the wire is witliout insulation, and its oidy su))port hetween two houses, the trunk of a tree, just now sheeted with water fi-oin falling rain. Tliis apparent indiilcrence to insulation in a telephone wliieli will overcome a resistance of eleven thousand ohms is not easilv ex})lained. This is only one of a multitude of paradoxes l)rcsented by the telei)hone. Tlie sound produced in the hOephonc by lightning, even when so distant that only the Hash can be seen in the horizon, and no thunder can be heard, is very characteristic, somctliing like the quenching of a droj) of melted metal in v/uter, or the sound of a distant I'oeket. The most remarkable circumstance is that this sound is always h(>ard just before tlic Hash is seen — that is, there is a ])robablc disturbance (inductive) of the electricity overhead, due to the distant concentration of electricity preceding the ais- ruptivc discharge. On Sunday, November 18, 1877, tliese sounds were heard and remaiked upon in Providence the first time for several weeks. The papers on !N[onday morning explained it by the report of thunder storms in Massachusetts on the preceding day. Frequent sounds of electrical discharge similar to that of lightning, but nuu^h fainter, are almost always heard several hours before a thunderstorm. This has just been exemplilied in Providence. The sounds produced in the tclciihonc by the auroral Hashes or streamers were observed in Providence by Prof. J(jhn Peirce, in Mayor June, 1877. I will give one further illu.stratiou of tlu^ delicacy of the tele- phone, this time in relation to magnetism. Tn June, 1877, Prof. E. W. Blake substituted for the magnet of the telephone a bar of soft iron, free from magnetism. When this was held in the line of the dipjiing needle, the telephone talked readily by the earth's magnetism. Put when the tel(>phon(5 was swaycil into a position at right angles with the line of the dipping needle (in the same vertical ])lane), it was absolutely silent ; and the BUEGUETS TELEPIIONE. 287 voice inoi'easod or faded o\it in proportion as the telephone was directed toward or rece cnci'iiy is wasted in ovor- comitiL^ friction, iind tiir fork soun cniiu'S to fcst. 'I'o Ji'ssimi the friction it, is usual to ciiiitloy jiapcr covered with a layer of lamp- black. Instead of the jieneil is sulistitutcd a siuaii pointed bristle, /Vy. 131. the weight of which is .so slijrht that it will not inodify the niotiou of the pronjf. AVith very little force the black can bo removed, leaving a while line on a dark ground. Fi'j. 135. The nso of a revolving cylinder, firound which the pa])or is wrapped, early suggested itself, and in the liands of Duhaniel the apparatus assumed the form .shown in lig. 185. The axis upon which the drum revolves is a screw, which turns in a lixed nut, Fig. 136. causing the drum to advance at each revolution through the distance between two consecutive turns of the thread, which i.s sufhcient to jjrevent one portion of the i-econl from ])eing sui)er- placed uj)on that which precedes it Fig. 136 shows the paper SCOTT S PHONOfiKAril. 295 nftrr it liiis liccii rciii(>\c(l iVinii tin' cvliiidcr and spi-cad out. 'l'\\r. dots, a, li, c, (■!<•., arc iiiado Ity aclix'Ic wliicli usually accdiu- |iaiii('S tli<' a|i|iai'atus. 'rii(MlistaU(,'0 Ix'tWci'M tln'iii iv|i|-cs(>iits tlic duration (if oiio second, ^riio amplitude, and peculiar character of each viliratioii an! clearly ^^howii, and to ascertain the rate of xibration it. is only iiecessury to count the nuinher of umlulationa between two consecutive dot.s. Devices have also Ihmmi made hy Konijr, with wliicli the result- ant vihrations arising from two or more notes emitted .sinmlta- neously may bo recorded directly from tlu; vibnitiiig bodies. The phono,Lrra|ih invented by M. Leon Scott does not require that tracing shall be made at the place wliere the sound origin- ates, but AvlKM'cver it can b(i lieiird. It consists of a hollow ehanibei', niad(! sufliciently largo to respond to sounds of the lowest audible ])itch, nKMinted before u eylinder, similar to that shown in lig. 135. One end of this resonator is left open, and the other is terminated by a ring, on which is iixed an elastie mem- brane. The air within the resonator i.s easily thi'own into vibra- tion, whieh is shared by the membrane. The latter carries a stylus, which also partieipates in the motion, and reeords it u))on the blackened 2)aper. The hinnan voice, the t(nies from musieal instniments, and even the rumbling of di.stant thunder are thus gra])hieally presented on paper. For recording vocal iinj)nlses one of the most sensitive instru- ments is the logograph, invented by W. 11. Bai'low, F. R S. The pressure of the air in speaking is directed against a membrane, whieh vibrates and carries with it a delicate marker, which traces a line on a travelling riljbon. The excursions of the tracer are great or small from the base line which represents the rpiiet membrane, according to the force of the impulse, and are prolonged according to the duration of the pressure, different articulate sounds varying greatly in length as well as in intensity ; another great difference in them also consists in the relative abruj^tness of the rising and falling inflec- tions, which makes curves of various shapes. The snioothnes:? or ruggedness of a sound hi.,i thus its own graphic character, 296 THE TALKING ^IIO^OQRAl'lI. independent both of its actual intensity and its length. Tlic logograph consists of a small speaking trumpet, having an ordi- nary mouth-piece coiniccted to a tube, the other end of which is widened out and covered with a thin membrane of gold beater's skin or gutta perclia, A spring presses slightly against the membrane, and has a light una of aluminium, which carries the marker, consisting of a small sable brush inserted in a glass tube containing a colored licpiid. An endless strip of paper is German r j'rolonrje*t Trnmbone uu in muod Hij. 131. caused to travel beneath the pencil, and is marked with an irregular curved line, the elevations and deoressions of which correspond to the force, duration and other characteristics of t.ic vocal impulses. The lines thus traced exhibit remarkable uni- formity when the same phrases are successively pronounced. IncompTthmnihility Rg. 138. Fig. 137 shows curves obtained by the interposition of a light lever between the membrane and the smoked gla.s.s, wlii(,'h is drawn a^ong beneath the style, whose excursions are much mag- nilicd by tlic lever. The curves show respectively the tongue trill or German r ])rolonged, the mark })roduced by the sound of a trombone, and by the sound of oo in mood. Fig. 138 shows a tracing from the utterance of the word incomprehensibility, with dillerent degrees of effort. It will be I.OGOORAPHIO RECORDS. 297 noticed that while a certain variation occurs, due to the energy, eai'.h sound preserves a si)ecific character. Kig. 139 sliows in tlie upper portion the cflect of words of quantity which require a largo vohime of air, and are maintained a rehitivcly longer time than the more explosive or inten.;e kind. The lower diagram is what the tracer wrote when the familiar stanza from Ilohcnlinden was repeated. A much more delicate instrunient for recording sonorous _xI'vA_ JVn(a/iM Deducting fj JJy turch ami Irumitxt /tmt arrayeit. To Join the drewi/ul revelry. Fig. 139. vibrations has been made by iisiiig the membrana tympani of the human car as a logograph. This is rejirosentcd in fig. 140. The stai)es was removed, and a short stylus of hay substituted, of about the same weight, so as to increase the amplitude of tlio vibrations and afford means of obtaining tracings upon smoked glass, as in the logograph experiments. The membrane is kept moist by a mixture of glycerine and water, and the specimen attached to a perpendicular bar sliding 'h an upright post, and 298 THK TALKING I'lIOXOfJUAIMI. moved by a ratchet wlieel. To tlio upright is attaclicd, horizon- tally, a iiu'tairu! stage six. inches in h'ligtli, upon whieli slides a carriage with aghiss plate, and having a regular movement given to it by wheel and eord. A bell shajied mouth-piece is inserted in the external auditory meatus and luted in position. Th(^ vibrations of the membrane, due to a musical tone sounded ill the bell, may be observed by means of a ray of hght thrown Fi'j. 140. upon .small specula of foil attached to the malleus, incus, or to diil'erent portions of the membrana tympani, or may be recorded on smoked glass by a stylus fasteneil to the descending process of the malleus or incus by means of glue, in a line with the long axis of the pi'oecss, and exteniling downward, so as to reach the ]ilatc of smoked glass, which is moved at a right angle to the excursion of the stylus ; the latter then traces a wave line cor- KUNIG'S MOXOXIETKIO FLAMES. 299 responding to the character uml pitch (->f the musical tone sounded into tlie car. As the glass plates present plane surfaces, and as the point of the vihrating style sweeps tlirough the segment of a circle, the curves obtained are apt to ho discontinuous, especially when the amplitude is great. To obviate this difficulty a sheet of glass is employed, having a curved surface, the concavity being presented to the stvlus. The sheet of glass is a section of a cyliniler whose scmi-(liameter is C(|uivalent to the length of the style. In this way the point of the stylus never leaves the surface of the glass, and the curve resulting from its vibration is continuous. The carbon lihu is preserved by pouring collndiou upon it As soon as this is drv, the film may be lloated off with water, and]ilaced upon a plane sheet of glass, or upon paj)cr, and varnished in the ordinary way. Numerous other methods of rendering sound-vibrations visilile to the eve might be cited. In general these methods iire of two kinds. They either aim at jirodueing a lasting record on paper, iiiass, etc., which may be preserved and examiiHMl at leisure, or they jiresent to the eve in a vivid way the sound vibrations as they arc actually transpiring. Of the latter class, one devised by Konig deserves a passing notice. A hollow chamljcr is divided by a thin menihrauo of caoutchouc into two compartments : one of which communicates through a tube to the mouth-piece, in front of which the sounds are generated; the other is .supplied from a pipe with ordinary coal gas, which issues from the com- partment through a fine buriu^-, where it is ignited. Any motion of the diaphragm will change the ])ressure on the gas, and either k'Ugtheu or shorten the jeL The movements of the llame when ^■iewcd directly are scarcely perceptible. To render them dis- tinct, they are receivi'd on a foui'-sided mirror, which is made to revolve. The image of the ilanie is thus lcugthene(l out into a luminous band. When the membrane vibrates, the upper edge of the band becomes serrated, each elevation being due to one sound-vibration. The instruments thus far desci'ibed, while able to lu'oduce 300 TUE TALKING PUONOGliAl'lI. rooords iin(l(inbtc'(lly convct, could jr<> no faillici. 1'lie records tlius made ,su;i:ge.sti'd no way of I'eproducing the sound. Hor ■\vas tills elTocted until ^Ir. Edison produced liis wonderful talk- ing phonograj)]]. In its simplest form the talking phonograph consists of a mounted diaphragm (lig. 141), so arranged as to operate u small steel stylus ])laced just below and opposite its centre, and a brass cylinder, six or more inches long by three or four in diameter, which is mounted on a horizontal axis, extending, each way, beyond its ends for a distance about equal to its own length. A spiral groove is cut in the circumference of the cylinder from one end to the other, each spire of the groove being sepa- rated from its neighbor by about one tenth of an inch. The Fig. Ul. shaft, or axis, is also cut by a screw thread corresponding to the s])iral groo\'e of the cylinder, and works in screw bearings; con- se({uently, when the cylinder is caused to revolve by means of a crank tli;i''i is fitted to the axis for the i)urj)ose, it receives a for- ward or backward movement of about one tenth of an inch for evcr\ tui'u of the same — the ilirectioii, of course, d'M)ending upon the way the crank is turned. The diaplu-agm is supported by an ujiright casting capable of r '^.istmcnt(lig, 142), and so arranged that it mav be removed altogether when necessary ; when in use, however, it is clamjx'd in a lixed [)osilion above or in f rmit of the cylinder, thus bringing tin; stylus always opposite the groove as the cylinder is turned. A small flat spring attaelied to the casting Morx'iixa OK THE i'hoxocuaph. 301 extends umlcrncath the diaphragm as far as its centre, and car- ries the stylus ; and between the diaphragm and spring a small piece of india rubber is placed to modify the action, it having been found that lictter results aro obtained by this means than when the stylus is rigidly attached to the diaphragm itself. The •dcUon of the apparatus will now be readily understood from what follows. The cylinder is lirst very smoothly covered with tinfoil, and the diaphragm securely fastened in place by clamp- inf its support to the base of the instrument. When this has been properly done, the stylus should lightly press against that part of the foil over the groove. The crank is now turned, while, at the same time, some one speaks into the mouth-piece of the instrument, which will cause the diaphragm to vibrate ; and, as the vibrations of the latter correspond with the movements of the air producing them, the soft and yielding foil will become marked along the line of the groove by a series of indentations of different depths, varying with the amplitude of the vibrations of the diaphragm; or, in otlier words, with the inllectit)ns or modulations of the speaker's voice. These inflections may, there- fore, be looked ujion as a sort of visii)lo speech, which, in fact, they really are. If now the diaphragm is removed by loosening the clamp, and the cylinder then turned back to the starting 802 Tin: 'j'Ai.Kixa piionogkaph. ])oint, \vc liave only to replace the diaj)liragm and turn in the same clircetion as at first to hear repeated all that lias been spoken into the mouth-piece of the apparatus, the stylus, by this means, being caused to traverse its former path ; and, conse- (juently, rising and falling with the depressions in tlie foil, its motion is communicated to the diaphragm, and thence through the intervening air to the ear, where tiie sensation of sound is produced. As the faithful rcprodnction of a sound is, in reality, nothing more tiiau a reproiluction <>C similar acoustic vil)raliiins in a given time, it at once bec(jiiu'S evident that the cylinder should be made to i'cv(jlve with absolute uniformity at all times, otherwise a diirerence, more or less marked, between the original sound and the reproduction will Ixjcome manifest. To secure this uni- formity of motion, ami ])roduce a jtractieally working machine for utitomatiially recording si)eeches, vocal and instrumental mu.sie, and jK-rfectly reproducing the same, the inventor lias devised an ap[)aratus in which a ])late replaces the cylinder. This plate, which is ten inches in diameter, has a volute spiral gi'oove cut in its surface, on both sides, ff(jm its centre to within one inch of its outer edge. An arm, guideil by the sj)iral upcm the under side of the plate, carries a diaphragm and mouth-jjicce at it.s extreme end. If the arm be ])laccd near the centre of the plate, anil the latter rotateh. Prof. A. M. Ikfayer has ob- tained magnitied tracings on smoked glass of the record on the Fi'j. 143. foil. The a]iparatus ho used consisted of a dcli(;ate lever, on the unch-r siih; of which is a ])oint, made as nearly as po.ssible like the jjoint under tlie thin iron ])late in tla^ jihoiiogra])li. Cemented to the end of the long{>r arm of this lever is a jwinted slij) of thin copjter foil, wiiich just touches the vertical surface of a smoked glass plate. Tlie ])oint on tlie short arm of the lever rests in the furrow, ill which are the depressions and clevation.s made in the foil on the (ylindcr. llotating the cylinder with a slow and uni- form motion, while the ]>late of glass is slid along, the ])ointof cop2)er foil scrapes the lamjililack olf the smokeil glass ])lato and traces on it the magnilictl ])ri)lile of tlui deprcssion.s and eleva- ti(ms in thef])earance to the (ye of tlu; im[)rfssions on the foil, when the sound of a in bat is sung again.st the iron ])late of the phono- 1 304 THE TALKING I'HONOGKAPH. f^nph. B is the magnified profile of tlicso impressions on tlie smolccd glass obtained as just described. C gives the apj)ear- anco of Konig's llanie wiicu tlie same; sound is sung (piite close to its membrane. It ■will Ik; seen that the ])rolile of the inij)res- sions made on tlie phonogra[)h, and the contours of the flames of Kcinig, when vibrated by the same compound sound, bear a close resemblance. Mr. Mayer finds that the form of the trace obtained from a ])oint attached to a, mem1)rane vibrating imder the inlluence of a compouml sound, de}icnds on the distance of the source of the sound from the membrane, and tlie same compound sound will form an infinite number of dill'erent ti'accs as the distance of its place of origin I'rom the mend)rane is gradually increased ; for, as you incrca.se this distance, the waves of the comj)onent3 of the compound sound are made to strike on the mend)rane at dilfer- cut jicriods of their swings. Vnv example, if the compound sound is fornie(l of six harmonics, the removal of the source of the sonorous vibrations, from the membrane to a distance eipial to ^ of a wave length of the 1st harmonic, will remove the 2d, 3d, 4th, 5th and (ith harmonics to distances from the mem- brane cipial, respectively, to ^, f. 1. IJ and 1^ wavedcngths. The conseipienco eviilcntly is, that the resultant wave-form is entirely changed by this motion of the source of the sound, though the sonorous sensation of the compound sound remains Tinchangcd. This is readily prove(l experimentally by .sending a constant compound sound into the cone of Konig's a|>pai'atus, while we gradually lengtluni the tube between the mouth-piece and the mcndjrane. The articulation and quality of the jihonograph, although not yet perfect, is full as good as the telej)hone was six months ago. The instrument, when perfected and moved by clock work, will undoubtedly reproduce every condition of the liuman voice, including the whole world of exi)ressioa in s[)eeeh and song. The sheet of tinfoil ur other ])lastic material receiving the impressions of sound will be stereotyped or eleetrotyped, so as to be multiplied and made durable ; or the cylinder will be made of APPLICATIONS OF Tllf: PUONOGRAPH. 305 a material plastic wlicii used, and hardening afterward, Thin sheets of papier- macho, or of various substances which soften by lieat, would be of this character. Having jjrovided thus for the durability of the phonograph plate, it will be very easy to make it separable from tlie cylinder jjroducing it, and attachable to a cor- re.sponditig cylinder anywhere and at any time. There will doubt- less be a standard of diameter and pitch of screw for phonograph cylinders. Friends at a distance will then send to each other phonograph letters, which will talk at any time in the friend's voice when put upon the instrument. IIow startling, also, it will be to reproduce and liear at pleasure tlie voice of the dead! All of these things are to be common, evcry-day experiences within a few years. It will be jjossible a generation hence to take a file of phonograph letters, spoken at different ages by the same person, and hear the early prattle, the changing voice, the manly tones, and also the varying manner and moods of the speaker — .so expressive of character — from childhood up! These are some of the private api)lications. For public uses, we shall have galleries where ])honograph sheets will be pre- served as photographs and books now are. The utterances of great speakers and singers will thci'c be kept for a thousand years. In these galleries spoken languages will be preserved from century to century witli all peculiarities of pronunciation, dialect or brogue. As we go now to see the stercopticon, we shall go to public halls to hear these treasures of speech and song brought out and reproduced as loud, or louder, than when first K[)oken or sung by the truly great ones of earth. Certainly, witiiin a dozen years, some of the great singers will be induced to sing into the ear of the phonograph, and the clectrot^'ped cylinders thence obtained will be put into the hand organs of the streets, and we shall hear the actual voice of Christine Nilsson or Miss Cary ground out at every corner. In public exhibitions, also, we shall have reproductions of the sounds of nature, and of noises familiar and unfamiliar. Nothing will be easier than to catch the sounds of the waves on the beach, the roar of Niagara, the discords of the sti ts, HOB THE TALKING I'HONOGUAPH. the noises of animals, the puffing and rush of the railroad train, of the rolling thunder, or even the tumult of a battle. When popular airs are sung into the phonograph and the notes arc then reproduced in reverse order, very cui'ious and beautiful musical effects arc oftentimes 2)roduccd, having no ap- parent resemblance to those contained iu their originals. The instrument may tims be used as a si)rt of nmsical kaleidoscope, by means of which an inlinite variety of lu^w combinations may be })rodu(!ed from the musical eom])ositions now in existence. The talking phonograph will doubtless be applied to bell- punches, clocks, complaint boxes iu puT)lic conveyances, and to toys of all kinds. It will supersede the shorthand writer in taking letters by dictation, and in the taking of testimony before referees. Phonographic letters will be sent by mail, the io\\ be- ing wound on paper cylinders of the si>;e of a flnger. It will re- cite poems in tho voice of the author, anel reproduce the speeches of celebrated orators. Dramas will 1)0 produced iu which all the parts will be "well si)oken— with good accent and good dis- cretion ;" the original rnatriee being prepared on one machine provided with a rubber tube having several mouth-pieces; and Madame Tussaud's figures will hereafter talk, as well as look, like their great ])rototypesl ^ The ])honograpli has quite passed the experimental stage, and is now practically successful in every respect, and must be regarded as instrumental in o})cning a i\oW field for scientific research, and making one more aj)plication of science to industry. Its aim is to record and reproduce speech, to make a iierinanent record ot vocal or other sonorous vibi-ations, and to recreate these vibrations in such a manner that the original vibrations may bo again imparted to the air as sounds. The tidking phonograi)li is a natural outcome of the tele- phone, but unlike any form of tele2)houe, it is mechanical, ami not electrical, in its action. In using th(5 jihoiiograph, it is found best to speak in a loud, clear voice, and with distuict eauneia- 1 StTibner'a Monthly MUj/aziiu, for April, ISTS. CHAKACTEKISTICS OF TUK I'HOXOGRAPH. 307 tion, that the vibrations may lie sliiirply ami deeply impressed on the foil. Attention must lie also g-j yen to the movement of the haudle, so that the ])assage, of the foil under the stylus will be uuitonu and steady. As tlie speed of the apparatus decides the distance between eaeli dent marked by llie sonorous vibrations, it must also decide the pitcli of the tone; when the sounds are reprodueecL A bass A'oiee \v\\} give only half as many vibrations as a soprano voice, one octave higher, and jirint half as many marks on the foil in a given sj)ace. If, in turning tiie instrument swiftly, the speed at which tliese marks pass under the stylus is in<;rcased, then the pitch of the resulting tones will be raised, and the bass voice may reapjiear as a soprano, or in a high, piping treble far above the pitch of any human voice. In a t'ontrary manner, l)y turn- ing the handle slowly, u soprano voice may reappear as a very deep bass. This curious circumstance, in connection with the sj^ecch of the phonogi'a])h, will undoubtedly make it necessary to employ clock work to move the api)aratus, in order that an ab- solutely xmiform rate of speed, and, consequently, rate of vibra- tion, may be ])reserved while the machine is m operation. The foil, after having been iniiiressed with the vibrations, presents a regularly lined or scored ap})earaiice. But so minute are the in- dentations stamp)ed in the groove that they can hardly be seen without a glass. The foil is quite soft, and is liable to injuiy, and it is proposed to make Hter(H)tyjie copies of the projier size to fit the cylinder of the plionogra[)li. Such cylinders will be }iermanent and durable, and can be used many times over with- out injury, or can be duplicated by electrotvping. The tone of the phonograph is usually rather shrill and pi^'ing, but this de- fect will vmdoubtcdly be correct(?d by improved instruments. It must be observed that, marvellous as this instrument is, it is still quite new, and it is impo.ssible to say to what degree of perfec- tion it may yet bo carried. It has already ojtened the door to an entirely new and nntriesent time operated npon sixty eii'cuits, between almost all (jf the principal cities in the country. The distinguishing principle of this system consists in com- binin^at two terminal stations, two distinct and unlike methods of single transmission, in such a manner that they may be carried on independently upon the same wire, and at the same time, without interfering with each other. One of these methods of single transmission is known as the double current system, and the other is the single current or open circuit system. In the doul)le current system tlu; battery remains constantly in connection with the line at the sending stations, its polarity being completely revers(>d at the beginning and at the end of every signal, without breaking the circuit. The receiving relay is providtxl with a polarized or ]iermanently magnetic armature, but has no adju.sting spring, and its action depemls solely upon the reversals of polarity ujion tlie line, withmit reference to the strength of tlie current. In the single cui-rent system, on the other hand, the transmissicm is effected by increasing and decreasing the current, while the relay may have a neutral or soft iron armatur(>, provided with a retracting spring. A better form, however, for long circuits, is that of the polarized relay, especially adapted to prevent interferences from the reversals sent into the line to operate the double current system. In this system, therefore, the action dci)ends solely upon the strength 310 Q IT AUK r r L K X T K LKeiving relay Rg (which, as before .stated, takes place at everv reversal in the jjolarity of the line currcMit) was givatlv lengtliened by the action of the static discharge from the line, so that the employment of the local relay S was not suffi- cient to overcome the difficulties arising therefrom. A rheostat or ivsistanee Xj was therefore placed in the bridge wire with the receiving instruments R^ and Rg, and shunted with a condenser cof considerable capacity. Between the lower plate of the con- denser and the junction of the bridge and earth wire an addi- tional electro-magnet r was ]ilaced, acting upon the armature lever of the relay R^, and in the same sense. The eifect of this ari'angement is, that when the cun-ent of one polarity ceases, the condenser c immediately' discharges through the magnet r, which acts upon the armature lever of relay Rg, and rc!tains it in posi- tion for a brief time hefore the current of the oppo.site polarity arrives, and thus serves to bridge over the interval of no mag- netism between the currents of opposite polarity. It will be seen that the cond)iuation of transmitted currents in this method differs materially from any of thos(> u.sed in previous inventions. The v are as follows: 1. When the first key is closed and the second open, -t~ 1 2. When the sec'ond key is closed ami the lirst open — 3 or — 4 3. When both keys are closed -|-3 or-|-4 4. When both keys are o[)en — 1 314 QrADuri'j.j-Lx: telegraphy. Here we discover another very important practical advantage in the system under consideration, which is due to the fact tliat the dili'erenee or working margin between the strciigtlis oi" cur- rent required to produce signals upon the polarized relay and upon the neutral relay, respectively, may be increased to. any extent which circumstances render desirable. Within certain limits, the "Teater this diflerence tlie better tiie iriictical results, I'or the reason tliat the range of adjustm ,■ v. o ■ neutral i-elay increases directly in projtortion to the nu. u, .e ratio of the resjiective currents has l)een gradually increased from 1 to 2 to as high as 1 to 4, with a corresponding improvement in the jiractical opei-ation of the apparatus. From what has been said, therefore, it will be seen that before it became possible- to produce a quadruplcx ajiparatus capable of being worked at a commercial rate of speed upmi long lines, it was essential that its component parts slioiild have arrived at a certain stage of development When, in the early part of 1872, simultaneous transmission in opposite directions was for .the first tune rendered j)ractieable upon long lines by the cond)ination therewitli of the condenser, the first step was accomplished. It now only remained to invent an equally successful ni'Ml'od of simultaneoiis transmission in the same direction, wl- v.ii, .s we have seen, was done in 1874. The application of o • ^''.ore of the existing duplex eond)inations to the new ''(. .' . <^^. o iorm a quadruplex apparatus, soon followed as a nut. '. of course. The following method of simultaneous transmi.ssion in the same direction was inven.ted in December, 1875. Fig. 145 is a diagi'am of the ajniaratua as ai'rangod for quadru- plex transmission. The lever t^, witli its appendages, constitutes the first or single-point transmitter, wliich is the same as that of the Stearns duj)lex, being operated by an electro-magnet Tj, local battery < and key Kj. The second or double-jvn ! transmitter consists of a quatlranguliir jilato of hard rubl l; '•, mounted u])on an axis, and capable of being oscillated by tue ana c, which is rigidly attached to it By means of a spring e^, the DIFFERENTIAL METHOD. 815 arm e prespos upon a roller fixed upon one end of the lever fZ, which forces the otlier end of the lever against the stop d^. The k'\'er d carries the armature of the electro-magnet Tg, which, like the single point transmitter, is operated by a local hattery and key Kn. The oscillating plate E has four insulated contact pointsy; g,fi, ffiy upon its respective angles. The contact levers F and G are mounted on axes at each end of the plate E, and Fi>j. 145. arc pressed against it liy springs Sj s^. When the transmitter is in a position of rest, as shown in the ligure, F is in contact with /and G with/,, and the iiarts arc kept in this position l)y the action of the spring c,. When key Kg is dcjircssed, the arm e is raised by the action of the electro-magnet Tg npcm the bent lever d : this turns the ])lato E upon its axis, and brings F into contact witli y and G with f/^. 316 QrADRl'PLEX TEIiEGHAPIlT. In tliis apparatus, as in the one previously doscribod, there are four (liHereut electrical conditions possible when transmitting two sinudtancous dospatclics iu tlic same dinx-tion, as follows: 1. Botli keys in a jjosition of rest. Tliis position is represented in fig. 145. Disregarding for the present the receiving instru- ments and their connections, the circuit may be traced as follows: Fi-om the earth at G through wires 9 and 8, contact spring h, lever ^j, wire 7, contact ])ointy"i and lever G, wires G and 5, and thence through the receiving instruments to the line L. Thus the line wire is connected to earth without any battery, and there is no current upon the line. 2. The first key closed and the second hey open. Tlie route is the same as before from the earth .it G to contact s])ring h. From this point it now diverges through contact l and 3B are n(!V(!r thrown together on the line at the same time, as in tlii" previous arrangement The receiving apparatus consists of two sounders, S, and Sj, which are controlled 1)}' two relays, Hj and \{„, fig. 1-15. I'he line wire Ij, on entering the receiving station, jiasses tiu'ough tlie coils of both relays, and thence to earth through the transmitting apj)aratus. Both relays are pro\-idcd witli polarized armatures. DIFFERENTIAL METHOD. 817 and are preferably constructed with two electro-magnets m Wj, arranged with their poles lacing each other, with a permanently magnetized armature between the (opposite! ])ules. The arriving current, entering the I'clay Jlj, passes through the wire 2 and coil /t, of magnet m and h^ of in^, which are so arranged that a -\- current will cause the jtolarized armature n to be attracted by ??ij and repelled by m, while with a — ■ current the opposite efl'cet will be produced. The armature of relay llj is provided with a retracting spring i\, and operates the sounder Sj by means of a looid battery /j. in the ordinary manner. The rehu' Rj consists of two electro- magnets p and ^^j, and its armature is also provided with a re- tra(!ting spring r^ ; l)Ut it differs materially from the other relay in the arrangement of its local connections. The polarized arma- ture o is held by the tension of the spring r^, not against a fixed stop, but against the; free end of a movable contact lever r, the opposite end of which turns upon an axis. The contact lever r is itself held against a fixed stop q by a spring 7,, the tension of which considerably exceeds that of spring r^. The local battery to is placed in the wire 22, leading from the contact lever r to the differential sounder Sj. The manu'T in which the receiving instruments operate in each of the four different electrical conditions of the lino is as follows : 1. No current. The local circuit of sounder Sj is kept open by the action of spring r^ on armature ?i, ami it remains inactive. The opposing branch circuits 23 and 2-1: of sounder S3 arc Ijoth closed by relay Hj, which render it also inactive. 2. Current of -\- V>. The relay Rj (which is affected by positive currents of any strength) o[)erat(>s sounder Sj. The armature of relay Rg is pressed more strongly against contact lever r, but not with safhcient power to overcome the spring q^. Sounder Sg is therefore unaffected. 3. Current of — B. The armature of relay R, is attracted toward its back stop, and S, is not affecte, lever t^, wires 2 and 3, coutact jioint o, spring O, wires 4 ami 5, battery li, wires G ami 7, contact pDint ?;, and spring Tn, tlienee hy ^viro 8 to line L. Tlie IjattiM-y B sends a -\- current to line. 2. First hy closed and second Icey open. Tlie route is now ^ 1 hiii|iii|i|iiiiiiiiiiiii^ 3B Fig. 14G. from earth at G, by wire 1 and spring h to point a, wires 12 and 7 and thence as before to the line. lu this case there is uo battery in eireuit, and uo current goes to line. 3. Second h-y cloned and first by open. Tlie route is now from earth at G by wire 1, spring h and lever t^, wires 2 and 320 QUADRU IT.KX TKLEURAPHY. 13, battciy 3H, wire 14, jioiiit Oj, spring O. wires 4 and 15, con- tiict point II ^, wj)ring N and wire 8 to tlie Jinc. Tlie large bat- tery 3B semis a — current to the line. 4. Both keya closed. The route is from earth at G by wire 1, spring I), ccjutuct ])oint a, wires 12 and 6, main battery B, wires 5 and 15, contact point n^, spring N, and wire 8 to hue L. In tliis case the lesser main battery sends a — current to line. The receiving apparatus consists of two sounders S^ and S3, controlled by two relays 11^ and Eg. both of wdiich have polar- ized armatures, and are constructed in the same manner as those described in connection witli the la.st method. The armature of relay Rj is jjrovided with a retracting spring rg, and o])crates the sounder S3 by means of a local battery Z^, in the usual man- ner. The polarized armature 7, when no current is ])assing through the line, is held by a spring i\ against the free end of a contact lever r, which is in turn held against tlie fixed stop q by the tension of a spring (/j, which considerably exceeds that of the spring r^. The manner in which the receiving instruments operate in each (jf the four conditions of the line is as follows: 1. Cur- rent of-\- B. The local circuit of sounder Sj is kept open by the action of the positive current upon the polarized armature of relay Ei, which is suflicicnt to overcome the tension of s})ring rj, and it therefore remains inactive. The local circuit of sounder Sg is kept open by the action of the positive current upon the armatun; li of relay Eg, in aiUlition to the action of spring rj. 2. No current. The armature j of relay Ej is drawn by tlie tension of spring r^ over against the contact lever r, thus completing the local circuit of sounderS,. The armature of Eg is held back ly spring /'g, thus breaking hjcal circuit of Sg 3. Current 0/ — 3 B. In this (uise the action of the negative current from the greater battery causes the polarized armature to press against the contact lever r and overcomes the tension of spring g-j, and thus, although the local circuit is still closed between the armature j and contact lever r, it is now broken COMBINED DIFKEKKXTIAIi AND BRIDGE METHODS. 821 between the latter and the fixed stop q, and Lence sounder S^ remains inactive. On the other iiand, the negative current carries the armature h of relay K^ to tlie left, closing the local circuit and actuating the sounder S3. 4. Current of — B. This cur- rent is not sulfieient to overcome the tension of spring q^^ and, therefore, the contact lever r continues to rest against stop q, and the local circuit of Sj is completed. Eelay Rj, which operates by negative currents of any strength, closes its local circuit through the sounder Sg. In this arrangement it will bo seen that a reversal of polarity upon tlie line cannot occur while a signal is being given by either key. This method may be readily united with any suit- able duplex method to form a (piadruplcx combination. Fig. 147 is a diagram illustrating a cpiadruplex: method, based upon that shown in fig. 144, but embodies several important modifications and improvements not shown thera This arrange- incnc was extensively employed for some time upon the Western Union lines, csjiecially upon the longer circuits, and was ftmnd to be, in many res})ects, far superiijr to that first introduced. It will be seen tliat no changes were made in the principle of the transmitting ])ortion of the ajiparatus, or the combination of cur- rents sent to line in the dilferent positions of the keys, but portions of the receiving apparatus were materially altered. In fig. 147 the polarized relay E^, and its accompanying sounder, are placed in the briilgc 5, 6, as before. The neutral relay, which was formerly placed in the bridge wire also, is discarded altogether, and is replaced by a compound differential polarized relay Eg. This is inserted, not in the bridge wire, but in the line and earth wires ; these respectively form the third and fourth sidt's of the bridge, of which A and B are the lirst and second sides. Thu.s, when the resistances A and B are made equal, the outgoing currents will divide e(|ually between the line and the earth, ami will neutralize each oth(>r in their eflectupon the relay Eg. The latter consists of two electro-magnets facing each other, with a polarized armature between them. When no current is passing, the i)olarized arinatiu'e is held in a central 322 QUADRU I'LKX TEriE(iKAl'IIY. position between two spring contact levers N Nj, ami the cir- cuit of tlic local relay S is conij)Ieteil tlirougli these and the armature lever. The springs of tlie contact levers N Nj aro adjusted with sufficient tension to prevent tliein from responding to the current of the small battery Ej at the sending station, but the additional current from battery Eg will overcome the spring LINE GROUND Fig. 141. of N or of N 1 , according to its polarity, and thus break the circuit of the local relay S, which by its back contact will operate the sounder Sg. The electro-magnets r r are arranged to act in con- junction with llg Rg upon the same armature lever, and are connected with a condenser c and a rheostat Xj in the bridge •wire, for reasons which have been fully explained on i)age 313. DIKKKKENTIAL METHOD. 323 cir- 1 tho , aro ndirig n, but spring LINE e circuit ;ratc the ;t in con- and are e bridge ige 313. Fig. 148 shows the connoction.s of another form of (jnadniplcx appai'at us, embodying several important im2)rovement.s that are not found in tlie api)ai?ituri lieretoforc described. Both receiving relays |{, and \i., are i)rovided willidilfercntial helices and polar- ized armatures, and in general the dill'erential method is employed i|i|i|ih^{i{i|i|i|i|i{i|i|i!iliF^ Fig. 148. throughout in place of the bridge. The relays Ej and 11 j may be constructed as shown in the figure, or according to Siemeus's pattern, Exijerience has shown that the latter form gives, on the whole, the most satisfactory residts, and it has therefore been adopted in all the more recent apparatus. The combination of 824 QUADIlfI'LEX TKl.K(iUAniY. tho outgoing cuiTciits differs from that employed in llic; original qu:idru])l('X, and is us {(^liows: Kj open and K^ open, eiirrcnt Iraversinj; line -|-4 I^ K J open and Kjj closed, " " '■ + I^ Ki closed an)rnitli'r local, of tliiDc cplln. A,, Ki y of No. 1 nM'i'iviiii; operator. K,, Slnifli' iioliiri/.cd ri'lay. 8i, Ucridviii',' soiindci' opi'ratiMl l)y dill". /,, SouniliT local, of Iwn vrUf. K.J, Ki'yof No. ;J fi'iiiliiiu o|H'rnlor. Tj, Sin;,'li! I'lirri'iil li'aii.'»tiit fnr compcnsalinp; TOHiftnnrc alani-(t i;* oitiaint'd. c, .'-lionld Imvo uliont t\\it'e as many stui'tH as i\ (liotli ln'inK ad- jUf*tal»lt'). Tin! condenHiT r.^ slionld rirroivo its cliarni' tlironuli abont half tile rt'sistancc rcipiirrd lorliolli. Kor exainpli', if tlu' nnm- htT of Hlu'cts n^qnlnMl in r, were lio, and in c^ mi (total '.KM ami the ^l'si^'ta^('l' ri'ipiired for liotli were uMKHi oliniH, c, wmild rcipiire l.(KHI and (', 1.1)00. OnlincHor lesH than 400 mileH the nrranv'i'mi'nt bUown iu flg. 14S answers uvery purpusu. 328 QIADIUI'LKX TELEfiUAPlIV, the strcngtli or polarity of the outgoing ciirrcut.s ; us tlie changes nocessarv to elTect llie jiroper ays at the sending station. By means of .suitaijly arranged eontactdevers, two iiidei)enilent loeal circuits are Ijrouglit into acticjii by the same armature in its dill'ereiit positions, s(^ as to actuate two independent souii'lers. The diagram shows the receiving instrument en- relay at one terminal station, combined with other well known a]H)aratus, in order to elleet the simultaneous transmission and reception of two communications, in the same or in opposite dii'ections, or i)oth, upon one cimductor. With the exception of the arrangement of contact-points and thi'ir respective hical connections witli the levers N and Xj, and armature n^, by means of which the latter controls the local cir- cuits which oj)ci'ate the sounders Sj and So, tlie construction of the receiving instrument is precisely the same as that used in the (piadruplex system, which we have just i;onsidered, and which is fully descrilteil on page '''24. As shown in the figure, the eon- tactdevers N and N, ihe receiving instrument turn freely upon suitable fulcrums at tlieir lower emls, while tlieir free ii]>pcr (mhIs, when at rest, are held against the adjustable contact points '/ '/i ^'y '^'^ tension of the adjustalilc springs r rj. A contact point is upon the n{)per extremity of the contact lc\ cr N; and ti^ is an insulated sto]) occupying a corresponding position upon the lever X,. The contacts q q^ are so adjusted as to allow the arm «j, which is rigidly attached to the arinaiure a, to play between the stops o and Oj ujjon the contact lescrs, Avhich limit its motion in each direction, except at such times as the armature (I moves with sullicient power to overcome the retracti! force of springs ?• 7"j, in which case the lever X or Xj i- sscd away from the contact y or 7 j until it strikes against inc adjustal'ile stop p or ;)j. The operation of the two indepenilent transmitters or keys K^ and K„, at the sending station, gives rise to four dilTerent elec- trical conditions of the line, according to their respective positions witli reference to each other, as follows : 830 Ql'ADRUPLEX TKI.EGRAl'IIY. 1. First and second keys botli open. Tliis is the position of tlie appanitus shown in tlie fignre. In this position of the keys botli main batteries are in eireiiit, seiubng to Hnea positive or 4- cnrreiit of -|- B + 3 ]J = -f 4 1?. 2. First key closed and second key oiieii. In this position both main batteries are also in eirenit, sending to line a negative or — current of — 3 B — B = — 4 B. 3. Second key closed and first key open. In this ])osition the smaller of the two main batteries only is in circuit, sending to line a positive or -(- current of a strength of -\- B. 4. First and second keys both closed. In this position the smaller battery only is in circuit, sending to line a negative or — current of a strength of — B. At the distant terminal of tiie line L, the a])])aratus is arranged precisely as shown in the lig\n'e. It is essential that one sounder (for example, S,) siiould respond solely to the movements of the key Kj, and the otiier snnuder, Sj, in like maimer to the movements of the key Kg ; while both should resi)ond when both keys are simultaneously depres.scd. The manner in which this result is accomplished will be understood by the following explanation of the elTect of each of the above meiition(Hl electrical conditions of the line upon the receiving instrument. 1. Positive current from both batteries (-(- 4 B). The local circuit of sounder Sj is open between the })oint o and arm Oj, and that of Sg between the lever Nj and the stop q^, because the action of the current upon the anuature a, teuding to attract it toward yi , , is strong enough to ()V(>rcome the tension of the spring r^, and force the lever Nj against the stop p^. 2. Negative cui'rents from both batteries ( — ■ 4 B). The local circuit of soumler S, is closed at the point of contact between arm (t^ iind contact lever N ; but that of sounder Sj is broken betwe(>ii tl, contact levcir X ami the stop 7, because the strength of the eurreut upon the lino is so great as to overcome the tension of th spring r, and force the lover N against the stop 2'- 1 DOUBLE ACTING RELAY. 331 aed 3. Positive current from battery 15 only (-)- B). Tlie local circuit of sounder Sj is broken between tlie arm rtj and the con- tact o on the lever N, but that of sounder Sg remains closed, because the power of the current upon tlie line, though sufficient to move the arm Oj away from the stop o, is not able to overcome thespring i\, and separate the lever Nj from the stoj) q^. 4. Negative current from battery B only ( — B). Tlie local circuits of both sounders Sj and Sg remain closed, because the strength of this current is sufficient to bring the arm a^ into contact with the stop o upon the contact lever N, but is not enough to overcome the spring r, and thus separate the lever N from the stop q. Thus it will be understood that the armature a is caused to assume four different positions corresponding to the four different electrical conditions of the line. When the armature is in either of its extreme positions the local circuit of the sounder Sg is broken. When the armature passes directly over from one extreme position to the otlier, it, of course, closes the local circuit for an instant as it ])asses the middle point, but not long enough to produce any effect whatever upon the sounder Sj, whicli remains inactive. Condensers Cj and Cg are connected to the artificial line A for the purpose of compensating the static^ di.schargc .)f the line. Tlie adjustable rheostats Vj and Y ., are used in order to regu- late the action of the condensers and render their charge and discharge nearer the same duration as that of the line. An independent condenser C is arranged with one set of its poles in connection with the main line L, and the other set with the artificial line A. No effect is produced upon this condenser by the outgoing current, as tlie potential oC the latter is substantially the same on each side. The incoming current from the distant station, meeting with the resistance of tlu; helices M Mj, flows into and charges the condenser, whicli remains charged until a reviTsal of tlie current tiikes place upon the line, when it instantly disciiarges itself and 3;i2 QUADRUPLEX TELEGRAl'IIY. sends a niomentavv juilsation throiigli tlio electro-magnets M M^, thus tending to liastt'ii the action of tlic receiving magnet ujion its armature at each I'eversal, thereby improving the signals upon long lines. Tlic eflcctive action of this condenser may be much increased if desired, by augmenting tiie resistance of tlie helices M Mj, or by inserting additional resistances between thest; and the jimetion of the wires leading to the condenser on each side. The double acting receiving in.strument here described, and shown in the figure, is equally serviceable in connection with the arrangement of main batteries illustrateil arul described on pages 314 and 318. The apparatus has been tested in practical service ujxm all of the longest circuits on which the (piadruplex system is worked from the Western Union 'I'elegraph Cum|)any's Xew York olRce, and continued in constant use for one week on the New York and Albany circuit with very satisfactory results. In i-egular practice, however, it has been found preferable to use two inde- pendent relays, thus enabling each opei-ator to adjust his own instrument. On l'"ebruary 7, 1877, a tost was made on a direct circuit lietwecn Xew York and (Jhieago, via Pittsi)urgh, Pa., a (lis tancc of itl3 miles, and the simultaneous reception of two com- munications in tlie .same direction was accomplished at a s]i(>ed of thirty words a minute on each of the respective sounders Sj and Sg. Fig. 152 shows a general plan of the quadruplex apparatus now in u.se on the lines of the Westiuni Union Telegraph Com- pany, and which embodies the more recent improvement.s. The transmitting devices, both in construction and moch; of operation, are jireeiscly similar to those referred to in connection with lig. 151, so that it will be necessary here to refer onlv to the effect produced by the o])eration of the two indei)endent transnnt- ters or keys, which is as follows: 1. Key K^ and K„ both open, in this position the entire batterv is in circuit, sending to the liiu; a netrative or — current of_B — 3B: -4B. JMI'HOVEI) JiKLAV. 666 2. Key K^ r.pcii uihI K^ closed. la tliis cast; liaUery B only is in circuit, sendin.ix to tlic lino a nogativf oi'^ — current of — B. 3. Key Ki closeil and Kg oiten. The entin; battery is again in circuit, but in this case with the positive or -f- pole to the line, sending a current of -)- 3 B + B = -j- 4 ]i. 4. Key K^ and Kg both closcil. In this position the battery - ' v«. Bonly is in circuit, sending to the lino a ])ositive or 4" current of + B. Thus it will be understood that the line is caused to assume loiu- distinct electrical conditions, corresponding with the four possible positions of the keys at the transmitting station. The receiving apparatus consists of two sounders, Sj and Sg, which are controlled by rekys 11 1 and R.,. The construction of R^ 884 QL'ADRUPLEX TELEGRAPHY. is tlic sumo in every particular as that lierctofoj-e described ; it being, in fact, simply a i)olarized relay capable of responding to positive anrl negative currents. "J'lie relay Kg, however, differs materially from relay R^ in the arrangement of its local circuit connections, by means of which the sounder Sg is ojierated ; and the improv(;mentu[)on the form of relay heretofore vised consists cliiefly in dispensing with one of the sujtplementary contact levers, whereby the ap])aratus is not only simplified, but made to work with greater facility and. certainty through long circuits. The noi'mal pf)sition of the apparatus, wlien neither key at the transmitting station is de[)r('ssed, is tiiat shown in the diagram. The manner in which tlie relays llj and Rg operate in each of the four electrical conditions of the hue mentioned, so as to cause he sounder Sj to res]K)nd solely to the movements of key Kj, and the sounder Sg in like manner to the movements of key Kj, and both in response to a simultaneous depres.sion of keys Kj and Kg, will be understood by reference to the following explanation : 1. Kj and Kg both ojien. A negative or — current from both batteries ( — 4 B). The local circuit of sounder S^ is kept open, becau.sc the ])olarity of the line current tends to hold the armature h of relay llj, on its back stop p. The local circuit of sounder .Sg is also open between armature _;' and lever r, because the current on the line is sufTicicutly ])owerful to over- come the spring r^, and hold armature j against stop o ; thus sounder Sg remains inactive. 2. Kj open and Kg closed. A negative or — current from battery B only ( — B). The local circuit of sounder Sj re- mains oi)cn between stop Pj and armature A, because the polarity of the curr(!nt is such as to hold the latter against stop p. The action of thisearrcnt upon relay R, is to cause its arma- ture y, assisted by spring i\, to move to the left and make con- tact with the lever r, but not with sufTicicnt force to overcome the retractile spring ^j, thus leaving armature / in a central position between stoj)s o and Oj, thereby closing the local circuit and operating sounder Sj. IMPROVED IJELAY. 885 3. K, closed imd K„ o|1(mi. A jiositivc or + current from both batteries (+ -t B). This current causes the armature h uf relay Rj to move to the left, thus closiug the local circuit at stop^jj and actuating .sounder S,. The armature,/ of relay R3 is also strongly attracted toward the left, ])ressing against the yieliliug lever r with suflicient force to overcome tiie sj)ring y,, and press the former against the stop Oj, thus opening the local circuit of vsounder Sg. 4. Keys Kj and Kg I'Otli closed. Positive or -(- current from battery B only (-|- B). Kelay Ilj, which is ;iri-anged to close its local circuit by positive currents of any strength, actuates the sounder S^ precisely as in the third case. 'J'hc current upon the line in this case is not of sufficient strength to hold the armature / of relay Rj against sto})Oj; con.sefpiently it moves, together with lever r, assisted by spring q^, to a central jDosition, thus closing the local circuit between armature / and stoj) q through lever ?•, thereby operating sounder S^. When the arma- ture y of relay Rj passes directly over from one extreme ])osition to the other: foi' example, from stop to Oj, it will be observed that the local circuit is closed for an instant, but not long enough to produce any effect wliatever upon the lever of sounder Sg. It is therefore obvious that, with the apparatus as arranged above, two conunuuications may be simultaneously transmitted over a single conductor, and the signals recorded with facility and accuracy. In order that four communications may be made to pass simultaneously over a single conductor, it is oidy necessary to (•ombine the apparatus here described with any out; of the several known methods of simultaneous transmission in opposite direc- tions. The arrangement in general use for the accompli.shment of this pui'pose upon the Western Union Telegraph Company's lines is that known as tlie differential metiiod. A system of du})lex telegraphy known as the bridge method may be used instead of the diflferential. or, instead of cither of these, a com- bination of the differential and bridge methods. In practice the latter lias been found preferable, more especially on the longer 33t) QL'AUULU'LKX TELKGUAl'lIY. circuits, where the sifjnals have tu Ix^ rctransmittod nutnmatically over ail adjniiiing circuit, in whicli case it is ahsoiutclv essential that tlic signals sliouUl Ijc reeonlod ])crl'ectly at the repeater station. Tlu' last nanieil ]>hiii is in operatii)n on tiio New Voiic and Chicago (inadrnplex circuit, an^anged so tliat signids I'roiii New York and Chicago are at Bullalo autoinatically retransmitted in either direction. Before considering the arrangement for repeat- ing from one circuit into anotlier, liowever, it will lirst he well to describe the difTerent instruments more in detail than we have yet done. A few words also regarding the setting up and adjustment of the ap2)aratus will not be out of place here. DIKECTIONS FOR SETTIN(; VV TllK Ql'ADRUPLEX. The diagram, figs. 149 and 150, will sufliciently explain the manner in which tiie instrument should be sot up and connected The smaller section of the batteiy B usually contains about one third the number of cells that the larger section 8 B docs. The rheo.stat z should be as nearly as ]iossible etiual to the internal resistance of (B-|- •^> B) =4 B. The resistance of y should be e(|ual to the internal resistance of th(> portion 3 B of the battery. TIIK WOUBI.E CURRENT TUAXSMITTEK. This is represented at T^ in figs. 148, 149 and 150, and is operated by the key K^ and a local Ijattery e^, usually of three cells. The double current transmitter is sometimes construc'Lou as shown in lig. 153, but a simpler and far better arrangement has been recently introduced, which is shown in lig. 154. The draw- ing is an end view of the transmitter, and shows the pole ehan'nnE apparatus distinctly. The adjustable contact screws a and a, are supported by and are in electrical connection with the post P, wliich is in turn connected with the line wire. The post also supports two contact sjirings Sj and Sj, which are insulated from it and connected by wires 1 and 12 with the ziijc and copper DOUBLE CURRENT TRANSMIITKR. 887 poles of tlio miiin battery, respectively. The lever l^ of tlie transmitter is connected with the earth. Tb& proper adjustment of this transmitter is a matter of the Fig. 153. greatest importance to ensure the succe.ssful working of the apparatus. In order that it may follow the movements of the a key with promptness, the play of the lever t^ between its limit- ing stops near tlie electro- magnet .should not exceed ^\ of an inch. The contact screws must be so adjusted that at a point 888 QUADRUPLEX TELEGRAPHY. about midway of the stroke of the lover t^ the springs S and S, will i)otli 1)0 ill t'oiituct with it at the same time, Imt for the shortest possible period. The easiest way is to lirst temporarily adjust the upper limiting stop at the opposite eud of the trans- mitter lever (^, so as to reduee th(> play of the level lo ^^ of an ineh. or about half the ordinary distauee allowed for a sounder. Then gradually raise the eontaet serew a until the spring Sj l)arely touches the l(>ver l^, being careful to move the screw no further than is necessary to do this. Then liwer the eontaet serew a,, and adjust the spring Sj in the same way. Finally, raise tlu; limiting stop at the other end of the lever, so as to give it the usual play of about tjV "'^ aninch. In its vibration the lever t^ should touch one of the sprinjxs S, or Sg a: the same instant that it leaves the other. If the springs are ''/''■ steil too far apart there will be a break in the circuit, as the lever will break contact with one spring before it touches the other.; if too Ti(Uir together, the battery will bo plac(Hl on short cinMiit too long, from one eontaet being made before the oIIkm* is broken. By careful adjustment this period can be rednecd to almost nothing, and the more accunato this adju.stment the better will be th(> pei-formance of the apparatus. TIIK SINGLE CURUIC.VT TR.VN'SMITTEK. This is similar to the transmitter of the Stearns duplex. The play of the lever of the transmitter should be about ^ig- of an inch between the limiting stops and the contact screw A, lig. 155, adjusted so that when the key is closed and the transmitter in the ]iosition represented, the spring B will be slightly separated from the contact point on the end of the lever D. <^':;# THE CO.HPOUND POLARIZKD RELAY. This relay is r(>proseiitcd by Rj, in ligs. 148 and 149, and the, sounder connected with it responds to the signals given by tlu; doul)le current tnmsmitter at the sending station. The relay consists of four separate electro-magnets, arranged, in pair.s, with their poles facing each other, upon opjjositc sides of a double SINGLE I'L'KUENT TKANaMlTTJiK. 339 j)olarizc(l armature. The connections and principle oC operation have already been explaiued in foniieetioii with lig. 148. Tlw proper adjustment of the annatui-cs luul local eontaet levers of this relay i'* a matter of much inijiortancc. and the following directions should be carefully observed : b'i". 150 is a perspective view (jf the coni])(>\ind rehiy, showing the contact levers and their adjustment. The electro-magnets M M should be adjusted by means of the check nuts at the back, so that their jioU's are at etpial distances from the opposite faces of tl-.e polarized armature a. Tlie play of the armature lever Fig. 155. is regulated by the screw stops pg and p4, which limit the move- ments of the contact levers NN, in one direction, while the stops pj and pg limit them in tiie other direction. To adjust these levers, the screws p^ and p^ should be withdrawn until tho contact points upon the armature lover a are touched by those upon the levers N N, upon each side, so th.nt tho loc.^1 circuit can pass through tho lover from N to N, whm the armatures is in a middle position, but will bo intorrui-itod by its slightest movement in either direction. The play allowed to the contact levers by the stops ^3 and p^ may be, with advantage, consider- 840 QUADRL'PLKX TBLEGRAPIIY. ably less tlian than that of an ordinary relay. The proper ten- sion of the s^jriuys ?i and n ^ depends upon the condition of the line current, and will be referred to hereafter. THK SINGLE POLARIZED RFJ.AY. Tliia is shown at R,, in fips. 147, 148 and 150, and is simply a Siemens polarized relay, which should hcidjustcd with a play about the same as that of the ordinary Morse relay. This may ADJUSTMENT OF THE yL'ADliUl'LEX S41 ir ten- jf the be, and usually is, constructed in the same form as lig. 156, l)ut without movable contact levers N Xj. is simply th a play rhis may ADJUSTMENT OK TIIK AI'I'AKATUS F(Mi WOKKINti. The said an*angements liaving been properly i.iaile at both stations, one station, which for convenience we will call station A, commences by sending signals from the i)ole ciianging traas- mitter 1\, having been careful to leave key Kg or k^ of trans- mitter Tj open. Station B then signals to station A in the came manner, which signals will be received upon the polarized relay II. If the signals come reversed, or on the back stroke, the direc- tion of the incoming current through the relay must be reversed. Station A next instructs B to gnjuiid. B complies by turning the urtu of the switch Q (lig. 149) from q^ to ([^^ which sends the incoming current direct to the eartli dirough the rcsistanci^ Z, which has already b^^.i . ' ^'sted to equal that of the entire bat- I tery (^Kj -)- I'^j)- Station '\. lusn grounds by placing his own switch in tiie same jicsition, ind adjusts his polarized relay Rj, so tiiat the armuf.ure will remain at rest indifferently upon cither its front or back contact stop, when placed l)y the finger. Next, station A closes the single current transmitter Tg by means of Kg or /cg ; turns the switch Q back to its original position, that is, to the left, sending the entire battery to line. Tin- resistance X (lig. 150) .should now be altered, until the armature of the polarized relay Rj remains indifferently on either side when l)laeed by the linger as before. When this is accompli.shed, the line resistance a",d rheostat resistance in X will be equal. To ol)tain the "lectro-stalic balance, station A transmits iloLs or dashes by nieai < of transmitter Tj, ;inrl at the same time alters the caj)acity of the condenser c^ Cg (lig. 149), until it neutnalizes the; discharge wiiieh takes place at the end of each signal, and is manifesteil u])oii the relay lip The electro-static bahuK'C of this relay insures that of relay Rj without further ])rec;autioii. Finally, station A again turns switeh Q to the right, upon point 7.,. and station. 15 now jirocecds to obtain 342 QUADRUl'LEX TELEGKAl'HY. asse.'3 from one extreme jiosition to the other by a change of polarity upon the line, the relay should not give a false dot as it pas.ses the central position. The contact ])oints of the local relay or repeating sounder S should be adjusted as close as those of an onlinary relay. The above described apparatus is suitable for use upon lines from 800 to 600 miles in length. For lines under BOO miles in length, the modification of the apparatus, shown in fig. 148, and which is of .somewhat simpler construction, is usually employed. Simvdtaneoiis transmission in ojiposite directions, at the rate f)f fifty-eight words per minute each way, is now carried on be- tween New York and Washington, by the apjilicatiou of this quadruplex method to the Phel|)s ele(;tro-motor ])rinter. This leaves two sides free for exchanging service signals, or for carrying on two .separate communications by the Morse appa- ratus. The arrangement for repeating from ou(! ([uadruplex circuit into another is very simple in principle, and consists in ])lacing the two tran.smitters of one line in the same local circuits with the corresponding receiving sounders of the other line. The dctivils are more fully dcsci'ibcd on page 355. By this arrange- ment New York is enabled to carry on four di.stinct communi- cations simultaneously with St. Louis, a distance of about 1,100 ADJUSTMENT OK THK g Lf ADKUPLEX. 343 he -^l[lt*-t4llf*---f "OO I3> 344 QUADRUPLEX TELEGRAPHY. miles, by means of a quadruplex repeater at Pittsburg ; and witH Chieago, 1,000 miles, by means of a repeater iit Buffalo. Although the quadruplex lias, in a great measure, taken the place of the duplex upon many of the lines between the more important telegraphic centres, the latter system is, nevertheless, still em})loyed to a considerable extent between points of less importance whore the business is not sufficient to keep the quadruplex constantly employed; and in numerous cases it forms, in connection with this system, both a convenient and valuable auxiliary for supplying direct communication between several different stations at one and the saine time. There are various ways in which these two systems may be combined so as to meet the numerous requirements of the ser- vice;, but it will be necessary to describe and illustrate here only such as are now in actual operation and by experience have been found serviceabl(\ A ))lan of the apparatus as arranged at repeating station, form- ing the common terminus of one quadrujilex and two duplex cir- cuits, is shown in fig. 157. By this combination two independent communications passing in the same direction over the quadru- plex circuit may be automatically retransmitted from the i^epeat- ing station over two separate and independent duplex circuits extending to dilTcrent points, wlille at the same time two com- munications passing in the opposite direction over the duplex circuits may be repeated into and over the quadruplex circuit. For convenience of explanation we will take an actual case, and suppose the repeating apparatus to be pla<;cd at Bos^ton, which is in connection with New York, 240 miles distant, by quadruplex, and with Duxbury and St. John, respectively 40 and 469 miles di.^Jtant by dujtlex. In order to effect the desired retransmission of the different sets of signals passing through the apparatus, it is necessary to form separate connections between the several receiving instru- ments ami the transmitters of the different lines into which the signals are to be repeated. This is done by means of the local circuits, in a manner wiiich will now be explained. '• COMBINED QUADRUPLEX AND DUPLEX CIRCUITS. 345 iittou Wo connects tlie local circuit of Rg in line L with that of the transmitter t^ in As ordinarily arranged for single circuit working, the relay Rj (fig. 167) of the New Yoric line L, operates the sounder Sj by means of the local battery Bj ; and key k^,t\\e transmitter t^, of the Duxbury line L^ by means of the local Cj. For direct through working, however, and in order that the received New York •signals may be communicated fronitlu; relay Rj to the transmit- ter i'K3- With the apparatus constructed and arranged as in fig. 159, the operation may be briefly smnmed up as follows : When key Kj is operated sounders Sj and S, will respond. When either K^, K.,, or K4 is operated by first opening the switches attached, sounders Sj, S4 and S5 will respond. COMIUNED DIPLEX AND ■ 'ONTBAPLEX SYSTEMS. 351 It will, tlioi'cforc, b(! readily uuderstooil that tlic following results may be obtained : 1. Station A may send a mcssagi; to C, and C at the same time semi one to A. both of wiiich may Ih! read at B. 2. A may send a message to B, and B at the same tiim; send one to A, both of whieh may be read at C. 3. A may send a message to C, and at the same time B may send one to A, which latter may also be read at C. 4. A may send a message to B, and at tlie same time C may send one to A, whieh latter may also be r<'ad at B. 5. A and G may simultaneously send messages to B, the latter of whieh may Ije read at A. 6. A and B may sinmltaneously send messages to C, the latter of whieh may be read at A. 7. A may send messages to B and (J at the same time. H. A may send two messages simultaneously to B, both <>f •which may be read at C. 9. A may .send two messages simultancou.sly to C, both of "whieh may be read at B. 10. B and C can work together singly, ])reeisely as in the ordinary closed circuit, Morse system : and, 11. When it is n(H required to work duplex, A can signal B or C with either of his two keys. All the residts which have been described are accomplished by means of a single main battery K, i)laced at one terminal Btiition A. Fig. 160 represetits a comljination of the above system with the quadruplex at a common terminal station, at whieh the connections are so arranged as to allow of the repetition of signals from one circuit into the other. Taking an actual case, as before, we will suppose the repeating apparatus to be located at New London, whieh, for convenience, maybe designated as station A. This is in eommunieation with New York, 12(5 miles distant, by i\ ipia,\ conlinn- onsly, witliout I'ejrard to what is passniir between stations A, B and "(A 10. New York may send two nicssuii-es simnUaneonsly to A, one of wiiidi may 1"! read at H and C, and at the same time two eonununieations may pass over tlie line to New York, one from A and the other from C, the latter of which may be read at A and B. 11. N(nv York may .send two mesi^ages simultaneou.=jly to A, one of whieli may be read at B and C, and at the same time rwo may pa.ss simultaneously over line L to New York, oiie from A and the other from B, the latter of which ma}'' be read at A and C. 12. New York may send two ine.s.sages simultaneously to B, both of ^vhieli may be read at A and C, and at the same time reeeive two from A. 13. New York may send two messages simultaneously to C, both of which may be read at A and B, and at the same time receive two from A. 14. New York may send two messag> s .simultaneously, one to A and the other to C, the latter of whicli may be read at A and B; and, at the same time, n^eeive two. one from A and one from C, the latter of which ma}' be read at A and B. 15. New Yolk may send two messages simultaneously, one to A, the other to B, and the latter be read at A and C ; and, at the same lime, reeeive two, n\w from A and the other fi-om B, the latter of which may be read M A ami C. 16. N(>w Yoi'k may receive two n.es.sages simultaneously from A, and, at the same time, transmit two di.stinet communi- oations. one to B and one to C. or both to eit arately, and both may be read at A. Finally, 17. Station A may, by projierly arranging the Wo and AW. divide the two lines L and L,, and station buttons ^l)erate P- each anil Ihi cin yrADllfPLEX UEl'K.VTKK. 355 sciiaratcly : llie foninT as a quailnijiU'x wire to Ntnv York, tlie liiUcr as cuiitiaple. ■ ■' diplex to 15 and C. V\ji. 161 shows a ],laii oi roniu'ctiiifi; tlie apparatus at a station fonniii,!^ llic coimnoii teiMiiiiius ol' two (piadniplrx ciiviiits, sirn. I hey will be retransmitted, one by relay R, and transmitter/,, and the other by relay lU and transmitter 1.,, over line L, to Jbill'alo. By simply (dosing the buttons W, W,, \V„ and W^, the two circuits liiay be divided at Cleveland, and worked .sejiarately. 356 QUADliUPLKX TELEGHAI'IIY. Ml (1? ^v III QUADKri'LEX KEPEATER 357 A / _^ III regular practice, liowevcr, the circuits are worlced in tlio fol- lowing manner, so as to facilitate the exchange of husinesa between tlie three points l>eforc mentioned : The buttons Wg ami Wg arc closed and W and Wj opened. When thus arranged, llnlTalo and Cincinnati are enabled to work together duplex, and, at the same time, Cleveland may work duplex to Buffalo over lino Lj, and to Cincinnati over line Lg. The transmitter /j and relay r^ of line Lj arc so located on the desk or table, with regard to the corresponding a])paratus (^f line Lo, as to facilitate; the adjustment of the several instruments. Quadruplex r(>peaters are similarly arranged for facilitating the exchange of business betvi'een numerous other })oints on the lines of the Western Union Telegraph Company, among which maybe mentioned Boston, Albany and Buffalo; Bull'alo, De- troit and Chicago ; and New York, Hartford and Providence. A combination of the two methods of du])lex telegraphy, known as the bridge and differential systems, but differing materially in arrangement from that sliDwn on page 311, is also used in practice. At Buffalo two comj)lete sets of (piadniplcx ajiparatus, on this plan, arc arranged by connecting the local circuits in prcei.scl'* 'he same manner as shown in lig. 161, for repi'ating signnls irom one circuit into anotiicr, and, by this means. New York and Chicago are enabled to exchange four ccmmunieatious simultaneously, over a single wire, between these ])oints, A second wire b<>twe(Mi New ^'ork and Cliicago is equipped with the quadruj)lex aj)paratus, and ])reeiscly the same arrange- ment as the al)ii\e is made at Buffalo fnr repeating from one circuit to the other. At N(nv ^'n^k, howevi^-, the connections arc such, lli;ii while itsnllice and ('liicagi> ;n'c working ilnplcx on one side, the latter may also woi'k duplex on tiie otluM" side with liny one of two or nioi-e bnnich ollices in New Yoi'k. The manner in wliich this is done will readily be understood from fig. I(i2 and the following ex|il;nKition, v/hich n'liilc to the arrangement for a l^oston wire, where it was llrst used ; the one for the Cliicago line, however, is just the same : 858 yr.ADuri'LKX THr.EciHAi'iiv, The complete quadniplex set in ('(Hiiicctiou witli tlie line L is supposed to 1k' at the New York main ollice. Soiuulers .s, and S^, and key k^, at a braneli olliee in tin; city, which we will cull station A ; and the a]iparatii.s consistinj^ of sounders .vj and S3, rep(>ating relay Wj) '"•'^'.V ^'^"2 '""^ Icx-al ])atteiy e^, at a second branch ollice, ■which \vc will call B, In order to provide for the simultaneous rece[)tion of two independent conununications over line L, from Boston, one of which shall be received upon rchiy 11^ and sounder Sj, and, at tlie same time, also, ii[)on sounder s^ at station A, and that the other shall be received upon relay Rj, souiuler Sj and u[ion sounder Sg at station B as well, while se[)arate communications are at the same tiuK^ beinparatus at the main olUco in the; manner shown in the diagram (lig. 162j. Here the route of th(! local or branch wire of the relay Rj maybe traced from the earth plate G^ at the main office, to battery e, wire 1 and armature of relay Rj to sounder Sj, and thence by wire Ij to sounder Sj and earth (i„ at station A. The route of the branch circuit of relay II3 is from earth plate CT3 to battery c^. wire 2, armature of repeating sounder M and sounder Sj, and thence by line I3 to sounder Sg and earth G4 at station B. The routes of transmitters T^ and Tg may be similarly traced, It will be noticed, however, that the arrangement of the branch line, as well as local conned' ins of transmitter Tg, differ materially from those of Tj, as in it nor- mal position the former should remain opei., and thus leave only the smaller portion of tliL' main battery on 'le line. The keys Kj and k^ are not provided with circuit iwsi.ig switches, and contact is nuuh; at the back point, instead f the front, as in the ordinary form. The normal position of these keys is that .shown in the ligure. in which they close the branch ci.cuit and cause the arin.ature.s a and «, of repeating relays m^ and ?»._, to be attraI1> am that th i--nal main o station g tl iUeo can, w ith equal faeility, bo read from s< milder ^, at )Uiii!i'r s will le the latter ofheo at the same time i iiav ly iie[ I )riv ni 10 cev am I euiisei(neiitly operating sounder S., a traiisniitler nil iM'iineh 1)0 sen(bng signals to Boston or to some )ffiee at that place. In a similar manner and at the same time, 360 QLADKUPLKX TKLKCiKAl'liY. station B may workdvijilex witli aiiotliorlirancli office at Boston, of wliieh at that j)laco tlieru an' Jive on one sido of the (juadru- plex and two on the otlier. Tiie. balancing and adjusting of the quadrnplcx, it will, of course, bo understood, is all done at tlio main office. A^i .- Fij. ic: The qnadruj)lcx; is also arranged to work in connertion with .1 single direct circuit containing any nuinbci' of ulliccs, and the plan has been found to serve an ivxccllcnt ])urpose in pi'actici^, as coniniunit'uti'in can thrrebv br ui.iintaim'd between a distant gUAURUl'LEX AND SINCILK CIKCUIT COMBIVATION. ',',01 ollit'(^ (HI the (i[u;ulruj)lex circuit ami any one of tlu^ ninnlxT on the single wire line. Fig. 163 shows the details of the arrangement as a(loj)tc lever ar(^ in like manner cut out by means of button W. When, therefore, the switches W,. lo^ ;;nd W are open, Wj turned to the right and keys Kj and k^ elo.sed, as shown in the figure, Chicago may exchange business with any one of theoflices on Lj, the signals being automatically r(^trans?nitted at St. Louis by relays llj, r^ ami transmitter T, and <,. At the same time St Louis ami Chicago may also work du]ilex, using key Kg and Rg for that purpose. By closing switclns W,, lo^ and W and turning Wg to th(> left, the two lines Ij and L,, as will readily be scvmi, may be worked separatiMy, tin; former as a i[uailruplev and tlii^ latter as a single Morse circuit 362 AHUANQEMENT FOR NEL'TUAM/INj. \Gi. rent which is generated iu it by the sudden change of potential in a neighboring wire. Fig. 164 shows the api)lication of the method to a single Morse line, but here it is of com])aratively liUle practical importance, fi'om the fact that these lines, as a general thing, can be su[)plie(l with strong currents, so that there is always sufRcient working margin to cover the difficulties arising from induction. The primary wire of the induction coil C is in the circuit of one line, and the secondary coil in that of the other. The coils arc so wound or connected to tin; lines that either will induce in the other currents of opjiosite direction to llio.se induced by the remaining jKirts of the circuit. TIk; electro-magnets represented at a, a', h and A , are employed for ])rr)(liicing the |)ro[)er retard- nvx e fTcct on the counter or neutrah/ing currents which are generated in. the coi's surrounding (J, and the adjustable resist- JNDIC'IKi.V JIKTWKKN' I'AKA l,l,l-;h I.IN'ES. 363 anoe li R (ifllu! shunt circnit scr\n to still furtlier modifv these (•iinvnts, so that their iietion is sulijcct to coiuplcte couti-ol. Tlu; luaiiner in which the cleviro is rcmlerLMl ell'ective will roiidily 1)o understooil from tlic; diiigram. Tiius, for iiist,'in(:'(\ if a current of any polarity is sent into thceondnctor A, a current of LmB Fi'j. k;,".. tlie opposite polarity will In; induced in tlie line B, owing to its elose ])roxiniity to the fposeri that ijm Fi'j. I GO. inducc(l b\' the ])roximity of the two conductors tc) one another, the proper action of tlu; instruments will not Ih^ disturbed. Tlie arrangcmeni for accomplishing the sauK; result between two ([uadruplex. circuits is shown in lig. [(io. It is evident that, with the bridge or dilferential principle, all that is re(pui'ed to ellect the end in \iew, is to cause the two artilicial lines to act 864 DOUBLE TRANSiMISSIOX IN' THE SAME WUECTION. upon Oiicli otlii'i' ill a luiiniu'r similar to tlio uclioii of tlic actual lines, and for this jmrposo an induction coil and system of mag- nets, similar to that just described, k inserted in the jiath of the two artificial lines at I. Fig. 166 shows an arrangement of condensers substituted for the induction coils, which has been in extensive use on some of the long lines in the (;eutral division of the Western Union Telegraph Company. If the inductivo effect of the two wires are eriual, the condenser E is alone necessary to effect the neu- tralization ; but when unerpnd, the two condensers ^ and G are required in connection with 1*]. EAKLV MKTIIODS OF SIMI'LTA.NKOUS TUANS.MISSIOX IN THE SAME DIUECTION. In October, 1855, A. Bernstein, of Uerlin, devised a plan for the simultaneous transmission of two messages in the same direction, which is shown in fig. 107. The transmitting ai)[>aratus consists of two independent cir- cuit preserving keys Ivj. and Kg in connection with batteries Bj and Bj, the former composed of, say 10, and the hitter 20 cells, as shown in the ligiire at station A. The movements of these keys produce three different electrical conditions in the line, according to their respective i)ositious with reference to each other, as follows: 1. First and second keys open. The route of the circuit may be traced as follows: From the earth ]>late (x, through wire 6, adjustable stops 5 and 4, wire 3, to adjustable stops 1 and 2 and line L. This m;iy be considered the normal condition of the keys, in which jiosition no current passes to the line. 2. First key <;losed ami second key open. The route is from earth plate to wires 6, 7, niain baltery B,, thence to lever l^ of key K p and wire 8 to stops 2 and 1 any wire U to stop 1, ami lino L to distant ollice. In this position ol" the keys tiio lari^-er battery Bj only is in t^ircuit, sending to line a positive or -f- enrrent of -f- 20. •1. First and second keys both depressed. The route of the eirciiii in this case is from earth plate G, wire (!, 7, to battery Bj, le\er /j ; thenco to stop 4, and wires 8, H, and Ijattcry for iVy. 167. Bj to lever l^, wire 9 to stop 1 ; thence to the line L and distant station as before. In this position of the keys both batteries are in circuit, S'Midiu'jr to line a positive or 4- current of + 30. At station B a rcceiviui.- instrument oi relay is made use of, composed of a single elcctrt>-magnet M, having thnje armatures li,, ll„ and Bo, to each of wliich an; attached retractile springs '.3' ;ti aid ?•, respectivclv, Witli local cu'cuits and so und ers S, anc IS 2) as sliown m the 1 igure. IMAGE EVALUATION TEST TARGET (MT-3) // 4. :/. % W/. 1.0 I.I m 2.5 2.0 1.8 L25 iU ii.6 %' 7 y -^ Photographic Sciences Corporation 23 WEST MAIN STREET WEBSTER, N.Y. 14580 (716) 872-4503 306 DOLliLE TKAXSMISSIOX IN' TIIK SAMK DIKECTIOV. Sounder >Sj sliould ]v.s|)on(l solely to llic movements of key Kj, and sounder So, in like manner, to tliu movements of key Kj, while both should responi' wlien keys K, and Kj are simultaneously dejjressed. Tlie manner in wliieh tliis result is attained will be under- stood by referenee to the following explanation of tlie efTeet of each of the previously mentioned electrical conditions of the line upon the receiving instrument M at station B : 1. The normal condition of the transmitting aj)paratus. No current to line. The local circuit of sounder Sj is open at ]ioint o, armature Kj being held against its back stop by the retractile force of spring r,. Armature Itj is, in a like manner, held against its back stoj), .'.nuature R3 rests ^ipon its back stop, owing to the retractile force of spring r^, in which position it will be observed that a local circuit is comj)leted, in which are included sounder S3 and both local batteries, but as the two latter have like poles together, their eflfect ujwn sounder Sg is sul)stantially neutralized; con- serpiently, the latter remains inactive. 2. Positive current from battery B, only := -|- 10. The local circuit of sounoint simultaneously with armature 1^,, bv which means the local bat1(!rv of sounder Sj is short-circuited, thus leaving the latter moperative. 4. Positive current from both batteries (B, and Bj) = -|- 30. The current upon the line in this case is sufllciently j)owcrrul to overconu' the tension of the retractile springs r,, r^ and r^, and force the armatures Rj, Rj and R3 against their resj)eetive front sto]is o and 0,, operating the sounders S, and Sj. Thus will be understood the manner in wiiich the resju'ctive armatures of the receiving instrument are made to assume their diflerent jxisitions with relation to the electrical condition of the line, so as to record the j)roper signal upon sounders Sj and Sg. Instead of the receiving instrument as devised by Mr. Bern- stein, viz. : a single electro-magnet, with three separate arma- tures, of different adjustments, three independent relays may be used, with local connections the same, without dej)arting from the principle thereof. A second method was also inviMited by Bernstein, in which he made use of both i)ositive anil negative cui'rents. liefcrring tio the diagram, iig. 108, it will be observed that the transmitters, or kcvs, arc circuit i)reserviiiir, the sketch ditleriuir from the original iu form, but not in ]>riiiciple. The operation of the two keys gives rise to three strengths of eurrent upon the line, according to their respective positions, with reference to eacli otiier, as follows: The normal ]K)sition of the keys is that shown m tlie figiuv, both, being o])cu. 308 DOIHLK TKAXSMlgSION IN THE SAMK DIUPXTION. Tli(> ronU' (if tlio eircMiit, in each of the before ineiitionod posi- tioiis of the keys Ky ami K;,, may he readily traced hy reference to the drawing. Key Kj alone sends a positive or -\- current of, say, 10 cells from battery R. Key Ko alone sends a negative or — current from the same battery =, — 10. When both keys are simultanooasly depressed, the negative B 9 T- 7 1 a Fig. 168. pole of the smaller battery is iasulatcd, and the larger battery lij sends a i)o.sitivc, or -f- current =, -j- 20. Bernstein's receiving apparatus, in this case, is composed of tiircc independent relay.s, polarized by means of the auxiliary local coils lip Kg and 11,, the two former being constant, and the latter controlled by the armature a^ of relay M2, as shown in the figure at stiition B. The sounders S, and S3 are operated by shunting, instead of opening and closing the circuit ill P sti So of th BKRXSTETNS METHODS. 369 The strengtli of the current in each of the anxiliary IncrJ cir- cuits l)ef()re mentioned may Ik; cliangecl at will, ]>y \iir\ in<; the adjustable resistance coils r^, r^ and ?•,. It should not, how- ever, Im! of sullieient power to overcome the tension of »i)rings Sj, ^2 and Sg. Tiie current from auxiharv local R,, circulating in Mj, 13, say, = -(- 10, and that of auxiliary local E,, circulating in ^^2, = — 10. 'J'hat of relay Mj is brought into action only when armature a^, of relay M2, makes contact with stop 0, at which, time a current of -j- 10 circnhites through M,. Bearing this in mind, it will be readily understood by the fol- lowing e.xiilanation how the armatures Oj, a^ and O3 of the receiving in.struments ]\r,, W,, and M3, respectively, are matle to assume positions, with relation to the three electrical condi- tions of the line, .so as to cause' sounder S, to respond solely to the movements of key Ivj, and .soui;dcr So, in like maimer, to the movements of key K^, whiK' both rcs[)iind when Kj and Kg, at the .sending stati(m, arc simultaneously dcpre.-iscd. 1. Kj alone depres.sed, a positive or -j- '-'ii'i'''iit to the line of -f- 10. The strength of this current, supplemented by that of the auxiliary local Kj, is sufi'iciciit to dvercomc the spring s^, and move the armature o, forward, thus breaking the shunt bet\» >cn stop Pj and armature ai,and leaving sounder Sj t(.) be actuated by local battery /,. The action of the line current upon relay ^f.^, in this case, tends to partially neutralize' the ell'ect of the auxiliarv coil Kg ; con.secpiently, the armaturt; «„ is held more lirmly by spring s^ in the jiosition shown. Armature aj, of relay M3, also remains on its back stop P3, 1 ecause the line current (viz. : -\- 10:) is not of sullieient strength to overcome the s|>ring s^. Tlnis the shunt around .sounder Sj remains unbroken, and the latter is inoiierative. 2. Key K2, depressed. A negative or — current of — 10. In this case, the polarity of the line current is such as to partially neutralize the etfcct of the auxiliary local Uj. The armature a^ is, in consecpienec, held 370 DOUBLE TRANSMISSIUX IX THE SAME DIKECTIOX. more securely by spring Sj against stop Pj, thus preventing a signal being given on sounder Sj. Armature a^ of relay Mj is carried from stop V^ *^° ''i because the strength of the line cun-ent, viz. : — 10, atUled to that of the auxiliary local ( — 10), is sufficient to overcome the tension of retractile spring Sj, thus breaking the shunt, and causing local battery l^ to operate the sounder Sg. It will here be observed that when armature Og connects with sto|i 0, the auxiliary local of relay M3 is closed, the strength of wliich (viz. : -|- 10) being the same as that froiu the line, but of o])j)osite polarity, it only serves to substantially neutralize the effect of the latter upcjn relay ^fj, and armature Oj is held inactive by the retractile spring Sj. 3. Keys K^ and Kg, botli depressed. A positive or -|- current of -\- 20. Armature a^ of relay M^ is' caused to move forward, thus breaking the sliunt, and allowing a current from local battery /, to operate sounder Sj. The line current in this case is of a polarity, and sufficiently powerful to completely neutralize the effect of the auxiliary local Rj and exert a force upon relay Mg, tending to attract its armature a^ ; but the latter is held in the position shown, against stop P„, by tlie retractile spring Sg. The armature a 3 of i-ehiy M3 is carried from stop P3 to stop Oj, because the line current is sufliciently ])owerful to overcome retractile spring S3, thus breaking the shunt and permitting sound<'r Sg to respond. Practit'ally, the method of using one receiving instrument having three armatures is a very unsatisfactory one, for the reason that the (effective attraction of the cl(>ctro-magnet for any one of two or more armatures is materially lessened whenever one of the others is in contact, or nearly in contact, with its poles. The manner of operating a register, or sounder, by closing and breaking a shunt, as in the system above described, would render it impossible to receive and record the signals with accu- racy at any considerable degree of speed. S on pc ba CO MEKXSTEIX S METHODS. 371 The use of three independent receiving instruments, though free from the objections just mentioned, docs not obviate the difficulties which were inherent in the systems of simultime- ous transmission in the same direction, invented by Stark and Siemens, in 1855, and which by the latter were considered insurmountable. THK ELECTRO-MOTOQRAPn. The salient featvi ^ in this discovery is the production of moti«>ii and of sound, v the st3'lus of tlie Bain telegraph instru- ment, without the intervention of a magnet and armature. By tlie motion thus })roduced, any of the ordinary forms of telegraph printing or sounding instruments or relays may be worked, thus making it possible to send messages by direct transmission over tliousanils of miles of wire, at the highest speed, without rewrit- ing, delay, or difficulty of any kind. More than this, the apparatus operates in a highly effective manner under the weakest electric currents, rendering it possible to receive and transmit messages by currents so weak that the ordinary magnetic instruments fail to operate, or even give an indication of tlie passage of electricity. Thus, when the common instruments stand .still, owing to the feebleness of current, this telegraph will be at full work. The apparatus is shown in figs. 169 ami 170. In fig. 109 A is a lever pivoted upon a universal joint C, and is provided at its extreme end with a screw F, tipped with l)latina, resting upon a strip of moistened paper, which is carried forward (in the direction shown by the arrow) by the drum G. This drum G is continuously rotated l)y clof.'k work. The spring S is used for the purpose of creating a pressure of the point F on the moistened paper. The spring R is to draw the lever to the left and against the point X. L is a main battery, K a key. The zinc pole of the battery is connected to the point F, while the carbon pole is connected to the metallic drum G, through the key K. Wiien K 872 THE KI.ECTUO-MOTOdUAl'lI. is olo>!P(l, tho clioinicals witli wliicli the jiaijor is saturated arc clocKiiiposcil l>v tlif jiassa.LTt' of tho cuiTctit tlii'()u;^'li tlic ihiikt, and the lever rests against the point X, closing tiit^ local cireuit containing the sounder AX and local battery LB. If the key K is opened, the normal friction of tin; ])!atina ])oint F upon tho j)apcr is so great that the spring 11 is insull'icient to keep it against the point X, and it is carried forwanl by tho rotation of the drum to the point 1), where it remains until the key K is agani closed; then, by the passage of the current, the friction is reduecil so as to be impercej)tible, and the spring R easily j)idls the lever against X, where it remains as long as the current is allowed to pass. As will be seen from this brief description, tho Fig. 109. lever is moved backward and forward by a di(T(M-cnco in frictions, caused by tlie decomposition of the ciii'inicals (a solution of chloride of sodium and pyrogallic acid), with which the paper is m(.)istened, by the passage of the current. Why the paper becomes so extremely slippery on the pas- s;ige of the current, the inventor is uiial)!e to state. Tlie a})])aratus is extremely sensitive, and can be worked over a cireuit of two hundred miles with tsvo cells of battery. Some idea of its wonderful .sensitiveness may be formed from the stateii'ent that by em[)loying a delicate construction of mechan- ism and using clock work to actuate the same, a movement of the lever has been obtained, sullieieut to close a local circuit, IS liel drj tlifl bej fnd thJ TlIK I'OLAUIZKD MOTOGHAPU. 37;^ with a current that was incajiable of discolorin^' paper, mois- tened witli potassic iodide, or of moving the needle ol" an ordi- nary galvanometer. Unlike a magnet, no secondary currents arc set up, upon o))ening and closing the circuit, to delay the movements of the lever; neither has it cores to consume more time, in charging and discharging, hut moves with a maximum cirect instantly. The plan shown in flg. 170 is called a polari/2ed motograjih. The key K alternately connects the batteries A and B to the lever of the motograph, one sending a positive and the other a negative current. The eui-rent from the battery A passes to the Fig. no. point X, thence through the paper to the point G, up through G back to the other end of the battery A. Thus hydrogeu is generated on the point F, which becomes slippery, while oxygen is generated on the point G, which retains its normal friction; hence the point G is carried to the right by the rotation of the drum. If the direction of the current be reversed by })utting on the battery B. hydrogen is generated fin the point G, which becomes slippery, and oxygen on F, which retains its normal friction, and the lever is thrown to the left. The diagram is arranged merely to illustrate the principle of the invention. In practice, a single battery and revei"sing key are used 374 TIIK KI.ECTUO-MOTCXJUAl'II. Mr, Thomas A. Edison, the inventor of the electro-motogi-apli, states tliat lu; has ;i machine in operation in his lal oratory con- stniotcd upon tlio prineiph; sliown in fig. lOil, with which he lias succcc(h'(l ill repeating automatic signals from one circuit into another, at tlie rate of oik; tiiousand two h(in(h-ed words per minute, an average of six thousand lettei-s, or twenty-four thousaiul waves per minute, conipelling the h>ver A (lig. IfiO) to move ba('l<\vard and forward from tlw; ]K)int on tlie left to the point I) on the right four ImudnHl times per second. By attaching an ink wliecl to the extremity of the lever, opposite a coiitiimous strip of paper moved l)y clock work, mes- sages transmittcil at a spec(| of several hundred words per min- ute may he recorded in iidc ; and hy attiiehiiig a local circuit to the ing i)oints and adiling a sounder tlnTcto, as shown in thf , tlie apparatus may he used as a Morse relay to work long hues of telegraph. CIIAPTKIt XTI. ET.ECTKIC CALL UKLLS. Thi'", introduction of call hells nr alurrns, wliioli liavc now bo- conu! of such cxteiiHive application in hotels, factories, elevators. and wherever else their service has lieen desirable, or where it lias 1)ccn found convenient to employ electricity for operating them, followed, as a matter of course, witli the early introduction of the electric telegraph. The invention of these instruments may, therefore, be said to date as far back as that of the tele- graph itself. It will reay a silk covering, and the whole wound together into a single strand, where they leave the case. COMIilXATION KEYS. With the keys above described it is evident that the signals last only so long as tho button is dep.cssed by the operator; it will also be observed that tho operator has no means of knowing with certaint}' that a signal hiis been given, and tliat he nmst therefore be still less sure of its having been noticed. To meet this defect, and ])rovidc a suitable arrangement for every rcqnirc- uicnt, a special combination is needed, such as is shown in fig. 378 KLKCTRIC CALL BELLS. 176. This consists of a case containing a magnetic needle, an electro-magnet, and the metallic contact springs a h and c d. One end of the coil of the electro-magnet J"] is attached to the screw e, the other to the line wire by tlie insulated screw V. The spring a h is connected to the binding screw r lead- ing to the battery, the other, c i/, to the plate at e, by wliich communication with the line is made through the coil of the electro-magnet. To the axis of the magnetic needle, A, is fas- tened a pm g, which presses against the platinum contact r, when the lower pole is attracted by the electro-magnet, and the needle Fill. 176. tlius made to take up the position represented by the dotted lines opposite which, on tlie cover, is the word understood, or liere. The axis of the needle is also in electrical connec- tion with tlio metallic back of the instrument, to which are attached the metallic plate p and ^ "nding screw q, so that all three are electrically connected. Tlic small })late connecting with C, a and r is insulated from the back, and a spiral wire n m joins ]{ (ilVIXCr TIIK SICXAI-S. 379 When the knob B is deprcs.scost E and wire c, comjilcting tlie circuit. Tlic .soft iron cores consequently become niagncti/.CMl and attract the armature which interrujits the eurnnit at 7-, tliis causes the cores to l)ecomc demagnetized again and the armature falls back again. '"C the spring, when the cin;uit is once mon^estab- ii.shed and an altraclion follows as before. Thus a rapidly vibra- ting movement id set up and continued as long as the button is depressed or the circuit remains closed by the needle j)in before referred to. 382 ELECriUC CALL llKLLS. By a slight modification of the connections in the bell instru- ment the apparatus can be used both as a vibrator and as an in- strument to give simple taps. Tlie general plan is shown in fig. 179, in which !M and e refer to the same parts as in the last. S is a switch which can be turned on B or E at })leasure. When it is on .!'] the conneciions are precisely the same as those just described and the apparatus becomes a vibrating instrument ; when turned on B there is no interruption of the current with the attraction of the armature, and the instrument simply re- sponds by single taps to each closing of the circuit by the push button. The path of the current, when the switch is on B and E, is sufficiently evident from the figure without further description. liQUliLK HKLLS. When it is desirable to ])roduce a very loud sound, double bells and double electro-magnets are usually employed in the vibrating apparatus. Figure 180 represents an arrangement of this kind. The current, arriving at the binding 2)ost C, follows the metallic strips in connection therewith io D and I)', thence through the coils M M' and strips 11 V, II' V to the contact springs II K' and armature A. From A the continuation of the circuit may be traced by way of 15 ami binding post Z, which DOUBLE BKLLS. 383 lead? hack to the Lattery. One of the bohbins, M for instance, is wound so as to produce a greater magnetic effect than that produced by the other W ; this causes the armature A to bo drawn towards M until tlie circuit of the hatter is broken at E ; M' now acts alone until interrupted in turn by tlic break at K', when the same alternation is begun anew. Thus, at each Fig. 180. vibration of the armature, one of the two bells is struck with considerable violence, and the noise, with raj)idly recurring strokes, is well calculated to arrest the attention. In double bells of this kind the line circuit is never broken by the vibrating armature — the elToct of this movement being merely to shift the current from one coil to the other. This, in 384 KLECTKIC CALL UKLLS. some particulur cases, is an advantage of considerable iiiijiort- ance. In general, the principle of all vibrating bells is that of the self-acting make and break; but, when the contacts are rigid |K)ints, the vibrations of the armature take place only within narrow limits, and the arrangement cannot very well be utilized for ringing a bell. Siemens has devised a plan, in his dial in- struments, which answers the purpose much better, by giving the armature a greater range of movement ; but the adaptation of this device to the ringing of bells for simple calls is a little trouljlesome, and, in fact, for general use, would be altogether too comjilicatcd. By far the most jireferable way of obtaining the desired range of stroke is that already described, in which a spring of some kind forms part of the path for the current, and Ivl 01 Fi'j. 18L which, with the attraction of the armature, follows the latter for such a distance as may be required. When one battery is to serve for operating several of the bells above described, the vibrators cannot all bejilaccd in one circuit, as each one interrupts the circuit in(lei)endently of the others; ami it is impossible, or rather imiiractieable, to make the arma- tures of tlie various instruments so that tliey will all vibrate in exactly the same time, or always be in unison. The plan generally adopted for such cases is shown in figure 181, where each bell, I, II, III, has a se]iarate conducting wire of its own, as represented by the numerals i, 2, 3, and a return wire, L L, serves for all. If, now, one of the bells is operated by the pressure of a push button in 1, 2 or 3, as the case maybe, w m ^•()^'-l^•TKURUl'TI^'(^ ciuci it hklls. 385 it acts -without in any way interfering Avitli tlie others, as they MH! all quite independent of the circuit thus interrupted. SINGLE BEIJ.S TO BK M'ORKED WITHOUT IXTEltHT^PTIXa THB CIHCUIT. The fault just noticed in connection with the vibrating arma- ture, causing a l)reak at each vibration, may bo remedied in a very easy manner simply by causing the armature to cut its owu magnet out of circuit after each attraction. The principle works very satisfactorily, and will be readily understood by reference to figures 182 and 183, wiiich represent two j^hascs of its appli- cation, m m arc the coils of the electro-magnet ; a, the armature to which the clapper k is attached by means of a rather stifE tiKjTiriy^ X -I H-i»r"-g. Mg. 182. Fig. 183. spring, and / an elastic steel spring, which readily follows the to and fro movement of the armature for a short distance. In figure 182, the armature itself forms part of a shunt circuit, by Avhich the current is withdrawn from vi m. As will be seen, a current arriving at C passe.-', through the wire 1, coils m m and wire 2 to the line L ; the armature is thus atiracted to the spring /, and a second route made for the current by way o? a c /. As the resistance of this route is exceedingly small, compared to that of the helices, almost the entire current jiasses by the new jiatli, and the cores become demagnetized. The retractile force of the spring now preponderates, and the armature falls against the back stop, breaking the shunt circuit on its way. ]?y this means the magnetism of the cores is again renewed, and a cou- 886 ELKCTHIC CALL JiKLLS. stant vibration kept up. In figure 183, the forward movement of tlie armature brings a spring / against a contact c, and forms tlie sliuiit quite independent of the armature. As citlicr of these arrangements does not breaic the main cir- cuit, any desired numl)er of tliem can be placi.'d in tlie same line and worked witliout interfering witli each otlier. Wlien the bell system is to be used for long distances, or when a very loud ringing is desired, for which purpose the main line current, as a rule, is not sufficient, a relay and local battery arc Fi(j. 181. generally used ; and with the heaviest apparatus, requiring still more power, the ringing is done by means of weights. Figure 184 represents an arrangement devised bv Aubine, in which a single set of electro-magnets, M M, serve both for the relay antl the call. A small projection on the upper end of the armature AKM WITH KK1.AY3. 387 still spring 2, tlioncc to lever 3 and its connecting wire to spring / and aniiaturo «, and froia there on tliroagli the coils to earth. This causes an attraction of tlie armature ; lever 3 falls down ou spring 4 and closes the local circuit, which again results in a magnetization of the core. The arinaturc is thus made to vibrate in the manner already described, and a violent ringing is set u]i, whieh continues until, by pressure on the knob h, lever 3 is agaiu raised and supported by the armature projection. Fig. 185. Figure 185 represents another relay based upon similar prin- ciples, and much used in France. The main line circuit is sufil- ciently ap})areiit without further explanation. The local battery B is inserted between the binding post K and Z. From K an insulated eojiper strip h h leads upward, and at the top is bent so as to catch the pin c, when the latter is carried upward by the spiral spring d. A ju'ojecting pin from the armature, wlien the latter is not attracted, serves to keep the rod F ^[ depressed. With the arrival of the line current the armature is attracted and 888 ELECTIUC CAIJi ]JKI,IA tlio rod rck'ascd ; this allows the sjiriiig d to act, and close the local circuit at e h when tho ringing,' is commenced. 15y pressing on tlie knob F the lower end dC tlio rod is caused to engage with the ])rojocting armature pin, and the api)aratus is onco more ready for another call. SIEMENS AND HAI.SKk's STATION ATiAUM. Tills is shown in figure 186, and consists of an ordinary relay and bell magnet, with an automatic rnako and break arranged upon the same principle as Siemens' dial instrument, vi in are tho coils of tho relay magnet, and 1^ and 1^ its terminal wires, one of which leads to line, tho other to earth. The ^jolesonlyof tho bell magnet aro shown at M M, one of its coils is connected to the binding post Z, the other to a V shaped piece of metal, termed tho shuttle, which, in its normal position, rests with ono end against an adjustable screw in the plate E, tho latter also iii metallic connection with the relay lever a. Tho local battery is joined to the binding posts Z and K. When a current is sent into the main line the armature a is attracted and closes the local circuit ; this charges the magnet M M and actuates armature A, but after passing a little distance the long projecting arm on the latter moves the shuttle against tho stop r and breaks the local circuit ; the spring F, being no longer restrained, now withdraws the armature, but in doing so causes the shuttle to close the cir- cuit once more, and thus a constant ringing is maintained as long as the main line is closed. HHKGUETS ALAUM OR CALL. With most of the apparatus heretofore described the call or alarm is only maintained for such a period of time as the circuit may be closed by the person giving the signal, or, as witli the arran;j,ement shown in fig. 184, until the messenger called stops the ringing by depressing the knob. Various other combinations have been suggested by Aubine, Breguet and otliers, by means of which a single signal is made to give any number of taps. BKKOUKT.S ALAint OK CALL. 889 390 KLKCTKIC CAl.li 11K1.L3. Brcguct's arrangement is shown in figuro 187, and its operation may bo described as follows: The line current arriving at L in consequence of the key being depressed, passes to the contact screw S, thence by way of the lever C c, pivoted at C, through the coils of the olectro-magnct P] to the armature a and contact b to earth. The armature is thus drawn forward for a short dis- tance, but returns immediately afterward, owing to the break in the circuit occasioned by the movement, and closes tlio circuit again. In this manner a vibratory motion is set up, and with each backward movement of the armature the toothed wheel R Fi'j. 187. is forced forward one cog, so that the lever c C is soon released from the pin g and fulls on the contact screw d, placing the local battery in circuit. The continued vibration of tlio armature keeps the wheel in motion, the arm D is thus brougb.t against the hammer lever, and the latter carried forward a certain dis- tance and tlien released, when the hammer strikes against the bell with considerable force. With the complete revolution of the wheel the pin g engages with the lover C c again, and onco more closes the main current. COMIIIXATK'V <>K f.M.I, IIKI.T, .\NI» JJKI.AY?'. 391 COMlUXATItA' OF A ! the wires S and Z when, therefore, the roJ F I is release.!, the action of the spring t^ brings the small jjlalinum tipped piece e against a sitnilar contact on Q and forms a second closing of .t'.ie local circuit, so that the bell continues to rii]g until the call has been observed and the knob depressed. SIEMKNS AKD UALSKK 3 UELAY WITH AXXUXCIATOR PLATE. These instruments are made in a very perfect manner, and are much used on the German Fire Alarm Telegra|)h. Fig. 180 rep- resents a perspective, and fig. 190 a sectional view of the relay, which does not diffjr materially fro:n tlic or linary forms, except in the addition of the annunciator disk and lever b c i/, pivoted at c. The relays are made for both open and closed circuits, the one represented being designed for closed circuits. The line connections are male at 1 and 2. K and B connect with the Morse recording ajiparatus, while the alarm bell is joined to A and the metallic piece "\v^ V. In its normal state the lever of the disk is held in a horiz )nt:d position by the hook on the lever a a, but with any interruption of the main circuit the ar- mature is drawn off by the action of s[)ring/ and releases the disk, wliicli is now raised to a vertical position by the weight h ; ihis closes the call circuit at t at t le same time tiuxt the armature a a, falling on t.ie back contact v/t, actuates the Morse recording KELAY "VVITU ANNL'XCIATUK I'J.ATE, 893 Fig. ISU. 894 KLKCTRIC CALI^ J3KI.LS. TTf* Fig, 190. CLOCK WORK ALARM. 395 instrument. Wlien the automatic vibratinj^ bell is used tlio ringing is kept up until the lever and disk are returned Xo their horizontal position by the operator. Fi'g. l!)(i. CLOCK 'WORK Af.ARM. Those oalls arc constructed in various ways, to suit the dilTerent purposes for which they are to serve; in some the hamincr is operated by weights or S[)rings, and made to give a single stmki' for cac'h impulse of current sent into the line; in others, tlu' strokes are reiicated a certain nunilier of times; or again, the ringing is continuous; but in all cases the current has only one function to perform, that of releasing tlie train of clock work. This is usually accomplished by tlie action of an electro-magni't on its armature, and tlie weights or springs cause tlie signalling. An important and much used ap[)aratus of this kind is that of llagendorlf 's, which gives but a single stroke for each depression 39G ELECTKIC CALL BELLS. of the signaling key, and which is therefore preferable to the vibrating "bells for many purposes, especially in places where the rattle oi the latter is likely to be more or less annoying. The use of weights or springs for causing the separate bell taps is also to be preferred to the tapping from a clapper canied by the armature lever, as with the latter arrangement, owing to an occasional tardy withdrawal of the hammer, the signals are not always very distinct. Fig. i;H. Fig. l'J2. Figures 191 to 194, inclusive, show the principal parts of Hagcndorfl's apparatus; the letters refer to the same parts in each figure. Figure 191 gives an interior view of the works. B B is p.irt of the brass frame to the back of wliich is attached an electro- magnet M ; fig. 19;] rcprcaetits the inside view of the same plate. The wheel I, fig. 191, is loose on the axis n' and carries a disk CLOCK M-OKIC ALARM. 897 g, better sliown in fignro 192 : this is provided with a detent S and spring F F, whicii ])resses the former into the teelii of the ratchet wlieel /, thus preventing tlie hitter, as well as tlu; wheel H, which is fasteneose, some exceedingly simple, and others more or less compli- cated. Fig. 197 shows a form of lamp devised by Duboscn, and oper- ated by the combined action of the current and a system of wheel work, driven by a spring in connection with one of the wheels. On a circular brass ])late A, is mounted a metallic tube B, to which is attached the binding post C. A m(>tallic rod D, sliding in this tul)e, carries at its t<)[) the arm E, to which is also attached ii rod and socket for holding the upper carbon. This rod is arranged to slide in the arm K, so that it may be moved up or d distance, and is held tightly in any position that may be given to it. The lower end of tlie rod D is pro- vided with a rack F, which engages with the wheel G, and the latter again is jircssed on to the axis of another wheel II, and 404 THK ELECTIUO LIGHT. firmly hM in jilace l)y friotioa Within a barrel connected with wlurl 11 tlicre is a ])i)\verf\il si)rinj,', which serves as the niotivo force for actuatini^ the ine('hanisin oi! the lanij). A (liiiil)le rack J, tenniuatiug above iu the rod (), which i)iusscs tlu'ough an Fig. 197. insnlatinjf j.niidc in the cover, and is ])rovided with a Roclsct for holding the lower carlxm, engaged on one side with the wheel IT, and on the other with the axis of wheel K. This wheel, iii like manner, engages with the ])inion of wheel L, better shown I DUBOSOgS UKGUI.ATOK. 405 in fi>(. 198, and tlie latter u^'uiii, with an endless screw M <>n the i>n)l(in^'-ati(>n of the axis, eurryinj,' th(3 cocn found, consumes about twice as fast as the negative. The use of wheels of different diameters thus furnishes the means for keeping the light at a given point, which is a matter of consider- ai)l<' iuipor':ince in almost all of tln^ uses to whi(;h it is a[)plied; and when a reflector is usnl, is absohitely neeessarv, as other- wise it would be all but inijuxssible to keep the light properly focused. Fig. 199 shows another form of lani|), (levis(>d bv Foucault, in this there are two svstenis of wln'cl wor one for l)ringing the rOUCAULT'S BEGULATOR. 407 ^^' is raised, and this movement is resisted by the spiral spring R, which, however, is not attached to the lever in (juestion, but to the end of another lever, pressing on its upper side and movable about the point X. The lower side of this lever is curved, so that its point of contact with the first lever changes, giving the spring greater or less leverage, according to the strength of the current In virtue of this arrangement, which is due to Robert Ilouilin, the armature, instead of being placed in one or the other of two positions, as in the ordinary forms of apparatus, has its i)osition accurately regulated, according to the strength of the current The anchor T Ms rigidly connected with the lever F P, and follows its oscil- lation:- If the current becomes too weak, t);c head t moves to the right, sto2)S the (iy o' and releases o, which accordingly revolves, and the carbons are moved forward. If the current becomes too strong, o is stopped, o' is relcaseil, and the carbons are drawn back. When the anchor T t is exactly vertical, !;• tth flies are arrested, and the carbons remain stationary. The curva- FARMERS AUTOMATIC LAMP, 409 I tiiro of tlie Icvor on vvliich the spring acts heing very slight, the oscilhitions of the armature and anclior arc small, and very slight changes in the strength of the current and brilliancy of the light are immediately corrected. Mr. Hart, of Edinburgh, Scotland, has invented a simple lamj), in which the weight of the rod in which the carbon is fixed supplies the jdace of the clcjck work in the lain]) ju.«t de- scribed, and an electro-magnet lets it descend, or locks it, as the carbons are consumed. - - Mr. Farmer, of Newport, R. I., has also invented an automatic lamp, containing but little train work, and whose action is con- trolled by a regulator or relay, consisting of an axial magnet, the coils of which are placed cither directly in the main circuit or in a branch of the same, and a delicately poised lever, frona one end of which the a.\is bar of the coil is suspendeil. The action of the current, when too strong, tips the bar in one direo tion, and when too weak a retractile spring tips it in the other. It is the employment of this relay to operate the mechanism of the lamp, through the intervention of loeal or branch circuits, whi.'h constitutes the jirineipal dilference betwtH'u tliis and Jiux^t of t'fc other forms of lamps now in u.se. The train of wheel WLi'k, driven by a spring, tends to cause the carbons to approach ., .i' oiher, but the motion is arrested if the armature of a small ■■l>-it< magnet, forming ])art i,( the apparatus, is attracted. The tii'.i g iiar .- aoves twice as ra])idly as the other. There are, be , conveniences attached to each of the car- bon pcncil-liolders, so that they can be disengaged from the screws and moved independently to any required position at pleasure. The holders, also, admit of separate adjustments on a vertic^J axis, so that by this means the carbons can be placed in a perpendicular line, one above the other. The spring iloes not need rewinding oftener than new carbons are supplied, and the performance of the lamp is very satisfactory. It has Ixjcn run for hours when required, and no reason exists why it should not run continuously until the jjcncils are consumed, provided it be jiroperly adjusted at first. AVithin the last two years a new form of electric light appa- ratus has been introduced in Fraiu'c and elsewhere, which, from the ri'iiiarkal)lc proj)erties that have been attributed to it, has attracted a great deal of attention. '^I'lie invention is due to M. JablochkolT, a liussian engineer, and is kimwu as Jabloehkofl's caudle. It consists of two carbons placed si, and S(>p- arate(l by an insulating and fusible, substance. No cloeiv work whatever is rcMpiired, and the light is very soft and steady Fig. 200 shows the arrangement as originally designed. '^I'he carbons «, /;, some four inches in length and one fpiarter of an inch square, are imbcddcil in an insulating sulistanee <: ; the carbon slips being also separati'd from each ollu'i" some three sixteenths of an inch aiK 1 t u! wnoi(! nioi dded into the si la pe jf a candle. In ord(>r to facilitate tla^ <'arlv act ion o f tl le 111 current, a small ])i(>co of carbon, about the si/e of the lend of ordinary leail pencil, is })laccd across the top of the electrodes. A series of experiments with candles of this ileseri|itioii were carri(Ml out at Chatham soiiu! time since, and, it is slated, the ]K>wer then obtained was some lifty j)er cent, greater than that obtained ])reviously from the recognized electric light JABLOCIIKOFF S CANDLE. 411 I Since then, M. Jiibloclikoff has twice modified tliis arrangu- ment, each modification ])cing attended witli success heyond tiiat obtained by the preceding. His first proceeding was to divest tlie carbons of tlicir outer covering, leaving notliing but the carl)on shjw a, }> (lig. 201), and tlie intervening substance, kaoHne, c. Each carbon is iixol in a small bra.ss tube d, e, the lower portions of which arc left vacant, so that they may fit over two metal pin.s, attachcil to which are the wires from the magneto macliine. These tubes are insulated one from the other, and the whole bound together by a band of insulating material/.' The latest modification embraces the removal of the carbons H Fig. 201. and the replacement of them by a carbon jiaste, a sort of prim- ing, the object of which is to reduce the resi.stanee which the kaolinc, when cold, intci'iioscs to the ])assage of the current. With this arrangement a .splendid band of light, constant, soft and steady, is obtained. Tlie principi.l ailvantages of the candU; appear to be due to the fact that it is lUMthcr dazzling nor blazing, and does not, tliercl'oi'c, surround the various objects illiuninatcd with the disagreeable h.'i/e and trhastlv shadows that are observed when tl 10 onniKirN' •l.vl ric hiilit If is.'d. It is, 1 lowcvi'i', somcw hat more cxpcnsuc, liut, as a <'orn[ii'nsation, is said to allow ol a 412 THE ELECTRIC LIGHT. greater subdivision of tlie onrrent — as many as fifty lights liaving been maintained from a single source by its use. A novelty in electric lamps lias just been brought out by Mr. Wallace, and, we learn, will soon be placed in the market at a veiy low figure. It consists principally of a substantial metallic frame and an electro-magnet. There are two slides in the frame, each capable of holding, in a hori:^outal position, the two carbons, which are made in tlie foi-m of plates, twelve inches long by two and a half wide, and half an inch thick. The upper and lower parts of the framework are insulated from each other, and in electrical connection with two binding posts, on the upjior part, serving to connect them with the magneto machine. The electro-magnet, through whose helices the main cuiTent circu- lates, is placed in the centre of the frame above the carbons, and, by its action on an armature, serves to separate the ujipcr carljon from the lower, to any distiuice desired. When the lanip is joined with a magneto machine by means of the binding posts and conducting wires, the circuit is com- jileted through the carbons, whicli touch eacli other, and the armature is attracted, thus separating and holding them apart so long as the current is maintained. The light burns toward the opposite end from which it started, then changes and burns back again, always burning toward the place where the carbons are nearest. If, from any cause, the light goes out, the circuit is broken, and, of couree, the electro-magnet ceases to act But the instant the upper carbon falls the circuit is again closed, and the carbons are once more separated and relighted. The advantages of this lamp are tliat it contains no coml)ina- tion of wheels or springs, and, consequently, there is n(j winding up of the apjiaratus to look after. The carbons, again, arc so large that they will last for ten nights, of ten hours eacli, and tlio lamp requires no care except for their renewal, '^riie practical disadvantage that suggests itself is its lack of means for main- taining the light at a given point, so as to use it in connection with a reflector. Figs. 202 and 203 show two forms of the Bru.^h electric lamp, as AIAGNETO-ELKCTKIO MACIIINKS. 418 mamifiictnird Ity the Tolcfri-aph Supply Compuny, of Cleveland. J''ig. 202 is u huiigiiig lamp, intended for factory use ; fig. 203 an adjustable table lamp. There are also a great many other lamps, such as SeiTin's, Browning's, Siemens's, etc., and all of which are more or less employed when it is desired to maintain the constancy of the light for long continuous working ; but the apparatus we have just described contain most of the princii)al characteristics and conveniences embodied in these, and it will, therefore, be un- necessary to give more attention to this j^art of the subject at l)resent. Instead of the battery, whose employment for light purposes is now almost exclusively confined to the illustration of lecture- room experiments, and physical demonstrations in class rooms, or to the production of luminous effects in theatrical exhibitions — places where it is seldom convenient to employ a steam en- gine — dynamo-electric nuiehines are now almost universally used, and their advantages over the battery are very marked in a great many particulars. Of late years, dynamo machines have also been extensively introduced in electro-plating establish- ments, to take the place of batteries, but in such cases their con- struction is ccmsiderably modified, in order to adapt thena to this particular kind of work. As ordinarily constructed for light purposes, the machines would have an electro-motive force far too high for plating, where, as a general thing, two or three volts are all that are re(piired. Largo magnoet-electric machines, for light purposes, a])pear to have beiMi first suggested by Professor Nollet, of ]irussels, in 1850, but since then a great many modifications and improve- ments have been introduced, so that the machines of to-dav, although depending for tlieir action, like the earlier ones, upon the same inductive princi^tle by which mechanical force is trans- formed into electricity, are nevertheless far superior to them, both as regards economy and efi'ectiveness when in action. Fig. 20-t represents one of the first forms of these machines as constructed by Holmes, of London, anoles liotwccii '.vliich it jiasscs : and tlio same iinmlit'i- of i:uiT('ii1s, ill altcniatt'ly ti|i|i()sii(' ilircctiuiis, arc generated in the foils. Tli;' cdil.s ran lie coiiiicclcd in difld'cnt \\a\s, acciU'd- ing as gi'cat olectro-niotivc l'i>rce or small resistance is recpiired. 'Plit; positive ends an- connccte(l witli the axis of the macliine, wliicli thus serves as the positive electrode; and a eonecntrio eylinder, well insnlated from it, is employed as the ncLfativo electrode. In I'So-i Siemens devised a very eU'eetive arnxalun^, which has since been much employed hy othci- maMufaetiirers in dill'erent Tonus of machines. The principal advantage of this armature residts from its occupying hut little space for rotation. Conse- quentl}-, it can be kept in a very strong magnetic lield ; at the same time also its form renders it well adaiited for rotation. It consists of a jieculiarly sliaped electro-magnet, such a.s wouM be formed liy cutting two wide and deep longitudinal gn^oves oppo- site each other in a eylindi'ical bar of iron, and then continuing tliem around the ends. 'I'he wire is wound lengthwise* around the core in the groo\e, like thread upon a shuttle, and l)rass caps, ))rovide(l with axes and a pidhy, ai'c then screwed on to tlie end.s of the magnet. When this armature is mounted between the poles of a series of jiermanont horseshoe magnc^ts and rotated rapidly, very strong euri'cnts are produced. The two ends of tlie wire are connected with a commutator, formed by fastening two semicircular pieces of ])rass to an ivoi'v ringon tlie a.xi.s and sjirings bearing upon tluve brass pieces, and in metallic con- nection with the binding [^ists of the apparatus, supply the means for collecting and comlueting awa\' the I'leetricity j>roduceil in the wire coils. By employing tw of the property whi .lughcr degree of magnetism than sttrl. and eon.ranehester, England, has succeeded in constructing \'ery enei'getic machines, and which arc well adaptcil for producing the electric light. o of these armatures and taking ad\anta!.;"e eh soft iron possesses of receiving a much 418 TlIK KM'XTIilC I.KillT. 'Plio n]i|>aratus in ivjility consists of two macliinoa comMncd in oiu'. Tlic curiviit from one of tlio Sicnu-ns's ariruitun's, pro- tliU'od l)y its ra[ii(l rotation in the strou<^ mairnctio liuld of a scries of [icrmancnt magnets, is employed to cliarge a large and power- fnl electro-magnet, between whose poles tlie second arniatnre is made to revolve, and the current from tli(! latter is utilized for the liglit. Twi> armatures for the eleetro-magnet are sometimes furnished Pig. 205, with the m.'icliine, one with wire coils for the jiroduetion of cur- rents of rather high electro-motive force, to be used for light puq)oses alone, and the other with coils of sheet copper strips, which give currents of less electro-motive force, but more esi)e- cially adapted for j)lating. With the interchangeable armatures, which are di'iven by belts running on pulleys on their axis, the machines can be used either for lighting or for ])lating at pleas- ure, and this, iu some particular cases, is a very desirable feature. r LADliS DVNAMOKMX'TKIC MACHINK •Hil Niimrnuis otlicr iimcliines arc ('oii>^tnu't('(l willi intorcliaiigoabic ai'iiialuri's, on tlic same |ilaii ami fnr the sann' jdirpusc. .\nntlirr form of iiia^riicto apparatus is that, ktiowii, from tlic naiiic of its inventor, as tin- Ladil iiiai'liiiic. This was lirst j)ul)liclv cxhiliiti'il at the Paris Hxposition of 18(i7. It is sliowii ill li,L^ 20."), and, as will be seen, employs, like the Wilde niacliiiic, two Sicincns's armatures, l)ut it dilTers from tiic latter princi])ally in not lia\in,t: any pi'i'inancnt niaLnu^ts wliatcvci' to eliarjijc the armature whicli supplies the horizontal Hold coils B B. Two Ion;.' flat pieces of soft iron are plaeeil within these coils .ind attached to the iron castings or pole pi(!ces .MM, XX, which are turned out just large enough for the armatures to fit inside of them and rotate without touching. Thick strips of l)rass or other nonmagnetic metal are also jilaeed between the upper and lower castings .\[ and .X, to keep them separate from each other, ami thus subject the armatures between them to the full f(jr(;e tter, how- ever, and much more convenient in charging a machine for the first tune, to use the current from a battery, nv from anotlier machine til i\'ady charged, than to depend alone, for this ellect, upon terrestrial magnetism. The machines thus far descriiied furiiisli only momentary currents of varying strength and [roduction of spark.s. !Mi'. /. ,1. Gramme has, however, invented a. machine in which these oiijcc;- tions are not met with, as the current obtained from it Hows contiimously, and in one direction only. The magnetic lidd in this, as in other machines, is created by a powerful magnet, of .;uch a sha[>e tiiat its poles confront each other, iind its cliaractcristic feature, thercifore, lies wholly in tlie construction of tlie armature. This consists of a ring of soft iron, siu'roiinded by an ciidless coil of wire, and is rigidly attached to an a.vis, so that it can bo made to revolve; on(! half of the ring being nmler the inHuence of the north pole, and the other under that of the south jxile of the magnet. • As the ring revolves, every poiMion of it changes position in the magnetic field ; but no current is develo[H'd in the wire, con- sidered as a whole, as the latter entirely surrounds tlu; ring, and tlio magnetic state of this, as a whole, remains unchang(Ml. A point on the ring considered In' itself, however, changes polarity GKAilMKS MACHINE. 421 twice (luring every rcvolutioi). As it recedes from one i»ole, it generates in tlie surrouiuliiig \vii'e :in olectro-inotivi! force, tlic same as tliat generated wlien it approaches the other pole, and the two e]ectro-moti\'e foi-ccs, conseciuentl}', ojipose each oflier, but wlienevei' an external conductor is provided between them, they unite and ])roduce a ciuTent. In ])ractice, the ring consists of a l)un greatest merit, is the invention of !Moses (i. Farmer, formei'ly of Boston, but now and iov the last three years elcetrician at the Government Torpedo Station, at Newport, K. 1. Fig. 207. Tliis machine, which has ])een somewliat moditied and im- proved upon from time to time by Mr. William WaUace, is, in many respects, unlike any of tlie other forms that we liavo con- sidered. It consists of two large electro-magnets, an armature, two commutators and four brushes, the latter forming ])art of tlio circuit, and sci'ving, when the macliiiu! is in operation, to collect the currents gencn the legs of the two magnets, and consist of wood or other im ire dnrahle insnlating snhstance, on which stri})S of brass, connecting with the wires from the armatnre coils, are secured The cimnections of the machine are so arranged that when e\-ternal circuit, which may consist of the light a[iparatus or depositing vats with their leading wires, is completed, the armature and lield of force coils are combinc(l with it in one — an arrangement for winch Mr. Farmer obtained a patent in 1872, and which, when the external resistance is low, is of very gi'cat advantage. The eight inch machine, so called from the length of its electro- magnet, and which is the one most commoidy employed, will pro- duce two lights of about two thousand candle power each, and is so arrangctl that tlm two may be (jombined in one if dt'sired. It weighs si.x: Inuidred ])ounds, and re([uires to drive it about one horse power for every twelvti hundred candle light. The machines made by Messrs. Wallace & Sons weigh from one, hundre(l ar.d twenty-live to three thousand pounds each, and are ca[)able of j)rodueing alight enual to that of from one thou- sand to forty thousand candles. Sonii! of them will e\en maintain the are with the carbons three and a half inches apart. l''ig. 208 shows another form of the light machine, as construct(Ml by the Telegraph Supply Co., of Cleveland, on a i)lan devised by Mr. C. i2i TlIK KLECTKIO LIGHT. BRrSHS DYXAMO-ELKCTUIG MACHINE. 425 F. Brush. 'J'liero arc two marked difTercnccs ])etwL'cu this and other luachinos, the fii'st of wliiili coi'sists in tlic peculiar iiietliod adopted for winding llio ariiialure; tl:e latter is coiii|ioseil of a ring or endless band of iron, l)ut instead t)f havitig a uniform cross section, like that of the Gramme machines, is jirovided with grooves or depressions whoso direction is at rijiht aimles to its magnetic axis or length. These grooves, which may be of any suitable nund)er, according to the uses for -wduchthe machine is designed, are wound full of insidated co])))er wire. The advan- tage of winding the wire in grooves or depressions in the arma- ture is twofold; first, the projecting portions of the armature between the sections of wire may be made to revolve very close to the ])o]es of the magnets from which the magnetic force is derived, liy this means the iniUictive force of the magnets is utilized to a much greater extent than is possible in the case of annular armatures as onbiiarily used, which are entirely covered with wire and cannot, therefore, be brought very near the mag- nets : second, owing to the exposure of a very considerable por- tion of the armature to the atmosphere, the heat, which is always develojted by the rapidly succeeding magnetizations and demag- nctizatiidl3'dissi})ated by radi- ation an much more economical than when ])roduced from any of the ordinary forms of galvanic battery. One iiorso ]io\vcr may be reckoneil as costing from tw(j to six cents ])cr hour, which would give the cost of ten thousand candle light as sixty cents per hour, simply for power. Of course some other items, such as oil, attendance, interest and depreciation, also cost of carbons consumed, would increase this amount somewhat, but even at twice or three times this cost it is still much less expen- sive than gas light at three eamllc light to the cubic foot per hour, at $2.50 per thousand for gas. The dilliculty of procuring carbons that would burn uni- formly has been a source of a great deal of annovancc. If tlie carbon is taken just as it (^omes from tlu^ gas retorts and sawed into shape, it is found to contain many impurities, and, -vvhea BRUSH S IMPHOVKI) OAIIHOXS. 427 biirnin;;, will frequently split and large pieces drop ofT. If it is first j>aiverized and tiieii pi'cssed int(j shape, as is done for but- terv plates, dilTiculties of one form or another still appear, ami tlic Ujiig voad of trial and failure lias generally had to be pretty well trodden over by all who have given this part of the sub- ject niueh attention. Mr. Wallace, who has studied it very clo.sely, has, we believe, succeeded in producing v(M-y satisfactory carbons, but we are, a.s yet, unacquainted with the process. The best illuminating effect appears to be produced from thin carbon pencils, but it lui,; heretofore been found imprai;ti- cable to use such pencils, on account of their high resistance aiul the rapid consumptiim of material due to the action of the air on their highly heated cuds. ^fr. Brush has sought to ob- viate these diflicultics, and at the same time improve the illumin- ating power of the light, by the admixture of different foreign substances with the carbon and by surrounding the stick either mechanically or by electro-plating widi various metals. By this nu^ins a free and ready conductor is afl'ord('(l for the current and a good coinieetion between the carbon and its holder securcvl. while the employment of longer and thinner p(>neils is also ren- dered jiractieable, and there is little or no liability to breakage. Ill operation the intense heat of the arc melts and disperses the covering of the carbon sticks at their opposing points and lor a pro[)er distance beyond, but no farther. The balance of tin? car- bons is entirely preserved, while as fast as tlu^y are burneil, just so fast will their covering bo removed, leaving the carbons exposed. Tlu^ subdivi-sion of the light is another of the problems that have occu[)ied the attention of inventors a great deal. JS'o one doubts that the division can bo effected, but to do this in a simple manner, and offer to the public a cheap and ])raetieal device for the jiurpose, has not been an ea-f J!, 000 candle powers oat'li, The best means, however, for obtaining- a niimlior of lij^lita from a single source consists in tiie emj)loyinent of thin strips of jilatinum or iridium, whose tcm]M'raturo is raised by the jiassage of the current to a ])oint oidy slightly below the melting ])oint of these metals. A\''hcn strips or wires of either metal are rendered incandescent, a mild and pleasant light is emitted, much less contracted and glaring than the light obtained from carbon pencils; and with the additional advantage also, that no vitiation of the atmosphere occurs, and the amount of light, at any one point, can be made as small as may be desired. Platinum, according to Mr. Farmer, affords about 100 candle light per square inch of incandescent surface, when within 220° of the point of fusioii, and a bar or wire of this metal can be maintained at this temperature for any length of time by means of a .suitable regulator and current. Iridium is even better adajitcd for illuminating purposes than ])latinum, as, in conse- quence of its higher melting point, it yields more light })er square inch of heated surface. While it is undoubtedly true that the light obtained in this wav is not the most advantageous for light-house and steamship purposes, or for places where the daz/.ling light of the arc is required, it is none the less true that for many other, and espe- cially for private or domestic uses, it possesses decided iidvan- tages over the carbon licrht. and on many accounts— among wdiich th(> facility attending its regulation is not least — is far preferable. 111- Its ips ho arc INDEX ABROAD, tlio telephone. Si. AccessoriuH mid couuectloiiH of tlio cnrboii telepUoiii', )i:i7. Anvil, lianiiiier luid xllrrup, 5. Auipuru uii the repulsion of dllTunrnt ele- inuntM of a current for cuch oilier, U."). Appllcutionri of the phono^ruph, :^).'>. Appt:calioii of pcrmuucut iiiuijnut:! to tclc- pliiinu, iOfJ. Appuraiiii for producing undiilatory ciir- reiiiH, 70. Artieiilutiiig telcpliono, fill. Arltetilaiu ^peeeh, truiixinisgioa of, 100. Atmo-iplienc vibrulions, 5. Ailantic cable, reaiutance of, 8G. Aiifii^'rapliic telegraphy, (JU. Auditory nerves, ij. .\ustiu, Charles K., telephonic experiments. HELi,, Professor A. O., upeakinji teloplione, l." ; researclies in teleplioiiy, 51), •'JO. Itell aill,ai. lieutley, Henry, experiments witli tele- I>huno.s, 'ri^'). Ueatsons researches i i telephony, 53, 113, U>J, Vii. Blake, I'rofeasor Eli W., contributions to the speaking' telephone, 3r4 ; use of railway tr.icii for. 70. OLiko, IJr. ciaionco .1., experiments with a plionauio^rapii made uul oi' a hiiiuau ear, t)9. Bourseilles, Charles, proposed telephone, 1-17. II itt^er'- Pulyteehnical >iote;i.ilati, Hi'. Ureguet's teli-puoiio and telephonic investi- gations, ^sr. CAiiBOM telephone, ; measuring rcsist- aii ■« of, 3i ; invention iif, 'Hi, Cable, workiui? telephone throiii;n, 8r. Centennial exhibition of telephone. 71). Channini,', Dr. WillUni t'., leleplionic inven- tions, ~ii, ar4. Characteristics of sound, 9") ; of tlie phono- graph, sor. Condenser, application to telephone, .31. Combination of the Morsj and liarmonic tel.-pnone, lii7. Constriicti m of the telephone, 83, 20.3. Correlaiion of forjes, 4,'. Clarke, Louis VV., researches and experi- ments in telegraphy. Tli, 2,0. Current induction, arrangements for neu- traliziiii,', 302. Currents, intermittent, pulsatory and undii- latory, 54. Curreats produced in the telephone, 391, Dei.ezennk's researches in telephony, i>(i, 117, 130. lie la Uive, researches In telephony, 55, 112, 131. niaphragm, vibrating, Ifi. Discharge of a Leyilen jar through an iron wire causes the wire to produce a sound, 122. Dolbeai's, Professor A. E., speaking tele- phone, 10, 75 ; researches, 2()<) ; ma.'neto- electrie telephone, 2IW ; electrophone, 2(17; projective Kpp.iratus, 2(i;l ; converti- bility of sound into electricity, 272. Du Moncel's researches in telephony, 5ti, llli; theory of the telephone, 2. Electric light, 40); Urusli's improved car- bons, 427 ; Brush's dynamo-electric m.i- chines, 423; Brush's autoinadc regela- tors, 412; cost of the light. 42i); Davy's experiments, 40); Duboscii's regulator, 40;) ; l-'ariner's automatic lamp, 400 ; Fanner's dynamo-electric machine, 42:); Foucaull's regubitor, 4iK); Oraiuine's machine, 421 ; Uiirt's lamp. 409 ; Jali- loclikoll's candle, 410; I.add's dynamo- electric machine. 419 ; mauiieto-electric machines. 413 ; Siemens'sarmature, 417 ; subdivision of the light, 427 ; tempera- ture of tiiu arc, 401, 480 INDEX. F oniiKii's law of vihratloiml foriiiH, ai9. GALVANIC milBic, 110. Gosslot'H resL'iirches in tc.leplioiiy, 55, 117. Galilco'B observations, SHIi. (iay-l-UHHac's difcovericx, 123. Gorf'sreHuarclici', 5(1. Oower'B, F. A., f.x|)i'riinent», SO. Gottoin dt! Comma's oljHcrvations, 129. Gray, Ellsha, teleplionlc ronearcliiin, 151,171; clectro-lianiioiiic Irli'iilioiii', W7 ; early t'xperlmi'iitH in ti'lepliony, IS') ; l)iitli-tiil) e.YJxTimunts, 1H7 ; violin cxpiTinii'nt, 188 ; plienomcna attending tlie tr,ii]<- niission of vibratory curreiitw. 171 ; dis- covery of tlie Hpeakiiif; telepliorn', LI ; transinlHsion of eomposlte tones, ISil ; telephonic Bpecifleations Hied in tlie United States I'atcnt OIHce, February 14. 187«, 217. Graphical method of physicists, 215. Graham, I'rofesso', theory of vibration of Trevelyan's liars, 11.5. Grove's experiment denionstraliii); the ten- dency of the particles of ma;;iietic bodies to yronp themselves under the liilluenee of nuii^netism in a loni;itudMial or axial direction, 128. Guillemin's researchea in telephony, .55, 112, 123, HENRY, Professor Joseph, telephonic re- searches, 14. Uelmholt/. on the human voice, 48 ; ana- lysis of the vowel sounds, 51, ill, U(KI ; what the lorm of the trace depends upon, ijo^l. ]^ ici.K's tubular electro-magnet, 101. OHM, or unit of resistance, lO:). On the disturbance of molecular forcei by magnetism, HI. On the convertibility of sound Into elec- tricity, 2;2. PAOK, Dr. Charles fi., researches in tele- phony, 11(1, 117,2,).'. Peirce, Professor John, experiments and In- ventions, 76, 271. Peculiarities of vibratory currents, K.l ; of coinpoun 1 vibraiions, 217. Phelp.s'a telephone, 21. Phonograph, ihe talking. 203; monndng of the. ;*)1 ; what clearness of articulation depends nnon. IWl. Phon lutograph, Jiurlow's, 205 ; KfSnig, 205 ; Scott's. 205; experiments with, liH. Phonographic records, tracings from, 303; diauias ; letiers, 305. Pill hot leleplione. 00. Plate, indexible, ;17. Poggendorff s nsearches in telephony, 55. Providence e.\periineiita i»ts. 76, 274. Preece, W. 11 , observations on the tele- phone, 82. Production of vocal sounds, 181. Properties of the pendnlum. 237. Producing the record of sound, 204, UADndiM.EX telegraphy, 30!l ; bridge method, 313; differential method, 315 ; combined dilTereiilial aid bridge meth- ods, 321 ; iirrangemeiit of apparatus for long circuits, 325 ; double acting relay, 320 ; single current tiausiiiitter, 3)8,339 ; adjustinentof the quad uplex, :Ul ; com- bined quadruple.^ and duplex circuiis, 315 ; arrangement for coiitraplex trans- inis-ion, 317; combined diplex und coii- traplex 8 stems, 310; combined diplex and coiitraplex systems, 319, .H5I ; com- bination of ipiiidriiplex and duplex sys- tem-', 3">3 ; qiiadrnplex repeater, 3.'>5, 357 ; improved rc'iav, 3W ; directions fo ■ set- ting up he ipiadriiplex. 3(6 ; the double current transmitter. 3:)(i ; the compound polarized relay, 3:)8 ; th single polaii/cil riday. 310 ; 'idjiistment of the apparatus for working, 311 ; combination of quad- Q v» INUEX. 431 <* niplcx mill (liplrx »v»t('iiis, liW: nr- niN^'riniMil riii'liraiicli iitlleoH, Uj!) ; i|imil- ni|iU:\ uiid Hiii^'lt! circuit rnnililiiutiiin, .'liil ; iirriiii<;ciiiuiit fur iii'iilruli/.iii); cur- rent iiiiliictiiin, .'11)3; iiiiliictli'ii butwot'ii iiHrallel Iiiich, .11)1 ; (luiiblu trav.MniHxiun III ilifsimuMilroctioii, .'itit ; otrly mt'tnodH •irHliiiiiltunuiiUijtrunMiiiiHHioii In tlii' Hniiiu (lirt'ctiiiii, 31)4 ; UuriiiitdU; h iiiutlioil, 310), REACTIVE cfteit of indiici'il oiirreiitK, 178. KuNOIIHIIt tluvici!!', liiruCiN of, Wi. Hemarks iiii lli • llicory of the teleplioiio, 3.S9. U.-eulv('ri<. ti'le|)liiiiiic, 3I!I. KiwarcliuH in ti;le|,'ra|- plicatioii of p^-rmaneni niai;iiets to, 2.VJ ; uccussories and connections of the c;ir- hon, 22r; Hell's, 17,50,21)5; battery, 32 ; Bailie's, 47; Hreijuet's, 2Sr ; Hour.seillu's, 147; Hentley's experiments. 225; cirrelu- tion of fore -a llhHtrated by, 42 ; carbon, 34, 223; C'lveat for, 217; currents pro- duced in, 21»1 ; conversation of Kiiglish Hcientists about. 8i; fhanuiti!?, Dr. Wil- liam F., inventions, 2r7; Uolliear's, lit, 75 ; double diaphrai.'in, 33 ; duplex, 21 ; diBtanceover which it can be worked. Ml ; 'Sdlson 3^ ; Kdison's ri'searchei. 218 ; electro - static, 2.31; electro • harmonic, )i)7; (iray's. 15. 73; Uray's tolepliotiic researches, 1,52 ; (Jray'selectro-harinoiiic, 11)7 ; tirav's caveat. 217 ; hanille, 27li ; iunumurablu uaun of, 45 ; llmsirutiuu of correlation of fornen by the, ■12 ; improve- ments tjy flniiiniiu,', Ulake. IVirce and •lonits, 2i'5 ; K. S. .Jones, liundle, 27ti ; limit of audibility, 38 ; inu-lcal, » ; Morse comlilnatlon, 41 ; magneto, 221; magnetic cores for, 177 ; I'help'H duplex, 21 ; Peirce's inoiithiilece for. 275 ; pill box, no ; Kelss's, !t, 148, 251 ; reiieater, 3« ; re- ceivers, 193, 21'J; remarkable phenomena, 3S1 ; siphon recorder, 279 ; Kiiniallini; apt) trains, 29, tM ; sensilivenessof, 385 ; switch, 10; speaking, invention of, 201; Thomson's report, 93 ; tones proiliiced by electric currents. 111, 1.39 ; theory of, 288 , vibratory bell, 41 ; vi.bratint,' dia- pliraj,'!!!, Itt ; vibratory plate, 48 ; work- iuu tliriiiii.'h cable, HI. Tone, li ; simple and composite, 8. Tracings of mr vibrations, 91 ; from phono- (jraph records, 31)3. Transmission of composite tones, 189. 'i'ransmitlini: reeds, 191. Tyudull's experiments, 156 ; lectures on sound, 240. U9KS of the phonoifraph, 30.). Uudiilatory currents, 5:1, 85, 208. Ijulveroity, Boston, 72. yAiii.Ev. Croinwell F., researches, t;2. Various forms of transmitliuj; reeds, 191 ; telephonic receivers, 1H3 ; traus- iiiitters, 197. Velocity of sound, 213. Vlbratin? plate, 48 ; rods, 2,39. Vibratory circuit breaker, 59 ; movements and inol.Tuiar effects determined in niaij!- netic bodies by the inttuence of electric currents, 117 ; lurrenls. peculiarities of, 173 ; motions of fluids, 211. Vibrations, propai;atioii of compound. 247 ; of Trevelya c's bars by the galvanic cur- rent, 113; of sound, optically exhibited, fi8. Vibnitional forms, Fourier's law of, 249. Visible speech, 68. WAOESEii's hammer, 140. Watson's. Thonas A., assistance in perfectluKthi' speakins; telephone, 71, 77. Wartmann's re-earches in telephony, .5.5, 113. Wertheini's researches in telephony. .V) ; on the elasticity of metals, 123 ; uiialysia of the mechanical effects manifested iu miignetism. lit, 128, 139. Western Kl ctric .Manufacturing Company telephonic apparatus. 31, 32, 33. WorKlni; telepho ie.i over artillclal lines, 103. Wheat tone's instruments. 104. Wil-on's. Charles 11., method for overcom- in)( current luductiou, 362.