America. The Galaxiidae are mostly fresh-water fishes and have a wide distribution in the southern hemisphere (southern parts of South America, New Zealand, South Australia and Tasmania, Cape of Good Hope), one species being identical in South America, the Falkland Islands, New Zealand and Tasmania. Their distribution has been regarded as affording support to the theory of an Antarctic continent in Tertiary times. However, several of the species spend part of their life, and even breed, in the sea, whilst others may be regarded as having become more recently adapted to fresh water, so that the argument derived from their range is not so strong as if we had to deal with exclusively freshwater fishes. The Cyprinodontidae are partly brackish, partly fresh-water fishes, whilst the Scopelidae, which are traced back to the Chalk, are all marine, many being inhabitants of great depths.

SUB-ORDER VI.-HETEROMI

Air-bladder without duct. Opercle well developed, parietal bones separating the frontals from the supraoccipital. Pectoral arch suspended from the supraoccipital or the epiotic, the post-temporal small and simple or replaced by a ligament; no mesocoracoid bone. Ventral fins abdominal, if present.

Families: Dercetidae, Halosauridae, Lipogenyidae, Notacanthidae, Fierasferidae.

Closely related to the Haplomi, but separated chiefly on account of the closed air-bladder. Mostly deep-sea fishes, some of which appeared as early as the Cretaceous period. The genus Fierasfer comprises small degraded fishes commensals of Holothurians and bivalve molluscs.

SUB-ORDER VII.-SELENICHTHYES

Air-bladder without duct. Opcrcle well developed. Pectoral arch suspended from the skull; no mesocoracoid bone. Fins with out spines. Ventral fins abdominal, with very numerous (15 to 17)

rays.

A very aberrant type, of uncertain affinities. Its only representative is the opah, Lampris luna, a large pelagic fish of wide distribution.

SUB-ORDER VIII.-THORACOSTEI

Embracing the Hemibranchii and Lophobranchii, but excluding the Hypostomides (Pegasidae), which the investigations of F. E. Jungersen show to be aberrant mail-cheeked Acanthopterygians. Air-bladder without duct. Pectoral arch suspended from the skull: no mesocoracoid bone. Ventral fins abdominal, if present. Branchial arches more or less reduced.

Families: Gastrosteidae, Aulorhynchidae, Protosyngnathidae, Aulostomatidae, Fistulariidae, Centriscidae, Amphisilidae, Solenostomidae, Syngnathidae. The two latter families institute the division Lophobranchii, in which the gill-lamellae are enlarged and form rounded lobes.

See articles SEA-HORSE, STICKLEBACK, and PIPE-Fishes.

SUB-ORDER IX.—PERCESOCES

Air-bladder, if present, without duct. Parietal bones separated by the supraoccipital. Pectoral arch suspended from the skull; no mesocoracoid bone. Ventral fins, if present, abdominal, or at least with the pelvic bones not solidly attached to the clavicular arch.

Families: Scombresocidae, Ammodytidae, Atherinidae, Mugilidae, Polynemidae, Chiasmodontidae, Sphyraenidae, Tetragonuridae, Stromateidae, Icosteidae, Ophiocephalidae, Anabantidae.

This series of families connects the Haplomi with the Acanthopterygii. The Percesoces are mostly marine, but the two last families are exclusively fresh-water. Some are inhabitants of great depths, others are pelagic, like the flying-fish (Exocoetus).

SUB-ORDER X.-ANACANTHINI

Air-bladder without duct. Parietal bones separated by the supraoccipital; prootic and exoccipital separated by the enlarged opisthotic. Pectoral arch suspended from the skull; no mesocoracoid bone. Ventral fins below or in front of the pectorals, the pelvic bones posterior to the clavicular symphysis and only loosely attached to it by ligament. Fins without spines.

Families: Macruridae, Gadidae, Muraenolepididae. Nearly all marine. The Macruridae are among the most characteristic fishes of the great depths. The Gadidae include some of the most valuable food-fishes.

SUB-ORDER XI.-ACANTHOPTERYGII Air-bladder usually without duct. Opercle well developed; supraoccipital in contact with the frontals. Pectoral arch suspended from the skull; no mesocoracoid bone. Ventral fins thoracic or jugular, more or less firmly attached to the olavicular arch. Gill-opening usually large, in front of the base of the pectoral fin.

The character from which this sub-order, the most comprehensive of the whole class, derives its name, viz.,, the presence of non

articulated, spiny rays in the dorsal and anal fins, is by no means universal, exceptions to the rule being numerous. Division I. Beryciformes.-Families: Berycidae, Monocentridae, Polymixiidae.

The most primitive of the Acanthopterygians, already well represented in the Chalk. A duct has been observed to be sometimes present between the air-bladder and the digestive tract. All marine, several bathybial.

Division II. Perciformes.-Families: Pempheridae, Serranidae, Anomalopidae, Pseudochromididae, Cepolidae, Hoplognathidae, Sillaginidae, Sciaenidae, Scorpididae, Caproidae, Centrarchidae, Cyphosidae, Lobotidae, Toxotidae, Nandidae, Percidae, Acropomatidae, Gerridae, Lactariidae, Trichodontidae, Pristipomatidae, Sparidae, Mullidae, Latrididae, Haplodactylidae, Chaetodontidae, Drepanidae, Osphromenidae, Acanthuridae, Teuthididae, Embiotocidae, Cichlidae, Pomacentridae, Labridae, Scaridae. The Percidae, Centrarchidae, Toxotidae, Nandidae, Osphromenidae, Embiotocidae, and Cichlidae are fresh-water fishes, the others are all or nearly all marine. Aipichthys, which is included among the Scorpididae, is one of the few Acanthopterygian types known to have existed as early as the Cretaceous period. See articles CICHLIDS, MULLET, MURRAY COD, PARROT-FISHES PERCH, PIKE-PERCH, SHEEPSHEAD, WRASSE.

Division III. Scombriformes.-Families: Carangidae, Rhachicentridae, Scombridae, Trichiuridae, Histiophoridae, Xiphiidae, Luvaridae, Coryphaenidae, Bramidae.

Marine fishes, several being pelagic and among the largest Teleosteans and swiftest swimmers. See articles HAIR-TAIL, MACKEREL, PILOT-FISH, SWORD-FISH, TUNNY.

Division IV. Zeorhombi.-Families: Zeidae, Amphistiidae, Pleuronectidae.

Division V. Kurtiformes.-A single family, Kurtidac, with a single genus and species from the Indian and Pacific oceans. Division VI. Gobiiformes. A single family, Gobiidae. Division VII. Discocephali.- A single family, Echeneididae. The remarkable remoras attach themselves by means of a cephalic disk to boats or to sharks, turtles, cetaceans, and other large swiftswimming animals. They form an isolated group, and have no real affinity with the Scombridae, with which they have long been associated.

Division VIII. Scleroparei.-Families: Scorpaenidae, Hexagrammidae, Comephoridae, Rhamphocottidae, Cottidae, Cyclop teridae, Platycephalidae, Hoplichthyidae, Agonidae, Pegasidae, Triglidae, Dactylopteridae. The "Mail-cheeked " Acanthopterygians include a great variety of forms, mostly living in the sea, the best known being referred to in the articles FLYING-FISH, GURNARD, LUMP-SUCKER, and MILLER'S THUMB.

Division IX. Jugulares.-Families: Trachinidae, Percophiidae, Leptoscopidae, Nototheniidae, Uranoscopidae, Trichodontidae, Callionymidae, Gobiesocidae, Blenniidae, Batrachidae, Pholididae, Zoarcidae, Congrogadidae, Ophidiidae, Podatelidae.

Nearly all marine, some deep-sea. Macrius amissus, which probably belongs to the Leptoscopidae, measures 5 ft. and is the largest known deep-sea Teleostean. The other members of this division are mostly small, Anarrhichas being another exception. The weevers (Trachinus) are dangerous stinging fishes.

Division X. Taeniosomi.-Families: Trachypteridae, LophoDeep-sea or pelagic fishes, some attaining a large size.

tidae.

SUB-ORDER XII.-OPISTHOMI

Air-bladder without duct. Opercle well developed, hidden under Pectoral the skin; supraoccipital in contact with the frontals. arch suspended from the vertebral column, far behind the skull; no mesocoracoid bone. Vertical fins with spines. Ventral fins absent.

Eel-shaped fishes standing in the same relation to the Acanthopterygii as do the Apodes to the Malacopterygii. The single family, Mastacembelidae, is possibly derived from the Blenniidae. Fresh and brackish waters of southern Asia and tropical Africa.

SUB-ORDER XIII.—PEDICULATI

Air-bladder without duct. Opercle well developed, hidden under the skin; supraoccipital in contact with the frontals. Pectoral arch suspended from the skull; no mesocoracoid bone. Ventral fins, if present, jugular. Gill-opening reduced to a foramen situated in or near the axil more or less posterior to the base of the pectoral fin. Body naked or covered with spines or bony tubercles. Connected with the Acanthopterygii Jugulares through the Batrachidae.

Families: Lophiidae, Ceratiidae, Antennariidae, Gigantactinidae, Malthidae.

Curiously aberrant marine fishes, many bathybial. The best known are the fishing-frog or angler, Lophius, and the Antennarius, which lives in coral groves or is carried about in mid-occan among the Sargassum weeds.

Division I. Sclerodermi.-Families: Triacanthidae, Triodontidae, Balistidae, Ostraciontidae.

Division II. Gymnodontes.-Families: Tetrodontidae, Diodontidae, Molidae. The Plectognaths are all marine; the recently discovered Triacanthid Halimochirurgus, remarkable for its long, tube-like snout, from the Gulf of Manaar, is the only form of this sub-order which is confined to the deep sea. Although so highly specialized, several forms, such as Ostracion (the coffer-fish), Tetrodon and Diodon, were already represented in the upper Eocene. See FILE-FISH, GLOBE-FISH and SUN-FISH.

OLOGY.

For bibliographical references to the Teleostomi, see ICHTHY(G. A. B.) TELEPATHY (Gr. Tλe, far, wáoŋ, feelings), or THOUGHT TRANSFERENCE, the conveyance of thoughts and feelings from mind to mind by other than the ordinary channels of sense. Although the word "telepathy " was first suggested by F. W. H. Myers in 1882, the suggestion had long before been made that the transmission of ideas, images and sensations could be brought about by other than the normally operative motor and sensory apparatus of the body. More than one writer had explained wraiths at the moment of death, clairvoyance and the phenomena of spiritualism by the theory of "brain waves." But it was not until the advent of the Society for Psychical Research that the hypothesis attracted much notice or was backed by carefully collected evidence. As used by the society the term is a mere designation, and implies no hypothesis as to "action at a distance" or the operation of any force not recognized by physical science.

time.

The earliest recorded systematic experiments in thought transference were made in 1871 by the Rev. P. H. and Mrs. Newnham, and were continued for a period of some eight months with marked success; subsequent attempts showed no results of an evidential nature. A few years later the attention of the British Association was called to the subject by Prof. W. F. Barrett, and from 1881 onwards many experiments were made by members of the S.P.R. and others; in fact, the so-called "willing game was at one time exceedingly popular; the successes, however, depended largely, if not entirely, upon muscle-reading, and usually ceased when there was no contact between agent (the sender of the idea) and percipient (the receiver). The systematic investigation has followed two main lines: (A) experiments on persons, often in the hypnotic state, in which the aim was to transfer selected images, &c., and compare the guesses with the results which chance would give; (B) the collection and examination of records of phenomena such as apparitions at the moment of death and other spontaneous cases in which there is a correspondence between the psychical states of two individuals, usually remote in space from one another. The problems raised by the two cases are entirely different: (1) in A there is seldom any hallucinatory element (see HALLUCINATIONS), in B, though not essential, it is present in a high percentage of cases; (2) what is transferred is in A an image kept before the mind, in B the phantasm of the dying person when that person has prima facie neither endeavoured to transfer this image nor, it may be, even thought of the percipient; (3) the desideratum in A has usually been to exclude normal methods of perception, in B the problem is to show that coincidence will not account for the facts; for, whereas in A the relation of successes to failures is known, in B it is difficult to get statistics and to be sure that an abnormal number of successful cases do not figure in a census. Side by side with direct experimentation, the S.P.R. collected firsthand records of apparitions at or within twelve hours of the moment of death. These, together with a discussion of the experimental evidence, were issued in 1885 under the title of

Among the chief experimenters may be mentioned Prof. M. Dessoir, Mr Guthrie, Sir Oliver Lodge and Prof. Sidgwick. In experiments conducted by the latter and Mrs Sidgwick at Brighton with numbers as the objects to be guessed, 617 trials were made with the agent and percipients in the same room: the numbers were between ten and ninety, and ninety successes were recorded, the probable total, if chance alone had operated, being eight. In a later series, conducted by Mrs Sidgwick, a similarly high proportion of successes was recorded; but when agent and percipients were in different rooms the results were not above what chance would give. These results were criticised by Prof. Lehmann and others, but were not seriously shaken; it was pointed out that the failure of experiments at a distance might be due to psychological causes rather than to the fact that the increase of distance eliminated the possibility of communication by normal means. In subsequent experiments, however, the successes in no series of any length were so far above chance as to give substantial support to a belief in telepathy.

Experiments in hypnotization at a distance provide some of the most conclusive evidence for telepathy. In 1885 trials were made both by Dr Janet and by Prof. Richet with the same subject. Out of twenty-five experiments the former held that nineteen were complete successes; Prof. Richet secured two successes and four partial successes in nine trials. The most striking point was that the hypnotic trance always coincided with or followed at an interval the attempt to hypnotize the patient; this is a feature of much importance in.considering the possibility of coincidence or of auto-suggestion.

It is usually impossible to prove that a dying person has been thinking of the percipient; much less can we show that there was any idea of causing his phantasm to appear. There are, however, small number of cases in which apparitions, of the agent or some other person, prima facie telepathic, have been produced experimentally. A singularly interesting instance is recorded by Wesermann, who tried the experiment in the early part of the 19th century; he wished to make the phantasm of a lady appear to a lieutenant, who was residing some miles away; at the time of the experiment he was, owing to an unforeseen visit, not alone, and his visitor is said to have seen the apparition also. More recently, in cases recorded in Phantasms

and the Census, the figure of the agent himself has been seen by the percipient.

The so-called reciprocal cases are evidentially of much importance. Each of the two persons concerned appears to receive a telepathic impulse from the other, so that each receives information about the other, or sees his phantasm.

Occasionally telepathic impressions from animals to human beings are reported, but the facts are usually far from well established. Telepathic communication has also been suggested as the explanation of the simultaneous movements of large flocks of birds.

Various theories have been put forward to account for telepathy, but they only agree in the total lack of an experimental basis. Broadly speaking, they are divisible into physical and psychical. Sir W. Crookes suggests that transmission is effected by means of waves of smaller magnitude and greater frequency than those which constitute X rays. Undulations starting from nervous centres are adopted as the explanation by Prof. Flournoy and others. But Myers and others regard the case against a physical explanation as complete. The main difficulty in the way of it is that the strength of the impulse does not seem, in the spontaneous cases, to vary with the distance, as by all physical laws it should. On the other hand, a curious phenomenon has been noted in experiments; if the percipient gaze at an arrow with its head turned to the right, there is a tendency, disproportionately strong if we suppose that chance alone operates, for the arrow to be seen reversed. This fact is, however, more important in all probability for the light which it throws on the mechanism of hallucinations (q.v.) than on that of transmission. Telepathy is often invoked as an explanation of the facts of mediumship (see MEDIUM, and POSSESSION); but it seems insufficient to explain them unless we assume for the medium a far greater power of reading other people's minds than experimental evidence has so far shown to exist.

BIBLIOGRAPHY.-Gurney, Myers and Podmore, Phantasms of the Living; Report on the Census of Hallucinations in Proc. S.P.R., x.; Podmore, Apparitions and Thought Transference; Mrs Sidgwick in J. M. Baldwin's Dictionary of Philosophy s.v. Telepathy; N. W. Thomas, Thought Transference (1905), containing a list of the important articles in the Journal and Proceedings of the S.P.R. and other publications. See also CRYSTAL GAZING. (N. W. T.)

TELEPHONE (Gr. Tîλe, far, and own, voice). Telephony is the art of reproducing sounds at a distance from their source, and a telephone is the instrument employed in sending or receiving such sounds. The term "telephony" was first used by Philipp Reis of Friedrichsdorf, in a lecture delivered before the Physical Society of Frankfort in 1861. But, although this lecture and Reis's subsequent work received considerable notice, little progress was made until the subject was taken up between 1874 and 1876 by Alexander Graham Bell, a native of Edinburgh, then resident in Boston, Mass., U.S.A. Bell, like Reis, employed electricity for the reproduction of sounds; but he attacked the problem in a totally different manner. This will be better understood if we consider shortly on what the chief characteristics of sound depend.

The sensation of sound is produced by rapid fluctuation in the pressure of the atmosphere on the tympanum of the If the fluctuations are irregular and non-periodic, Charac- ear. teristics the sound is called a noise; if they are cyclic and of sound. follow a regular and sufficiently rapid periodic law, the sound is musical. In connexion with the present subject it is important to notice the three characteristics of a musical sound, namely, pitch, loudness and quality. The pitch of a musical sound depends on the number of cycles passed through by the fluctuations of the pressure per unit of time; the loudness depends on the amount or the amplitude of the fluctuation in each cycle; the quality depends on the form or the nature of the fluctuation in each cycle. The necessary condition for a successful system of telephony is the ability to reproduce. these characteristics.

1" Über Telephonie durch den galvanischen Strom," in Jahresber. d. physikalischen Vereins su Frankfurt am Main, 1860–61, p. 57,

In 1831 Wheatstone by his "magic lyre" experiment showed that, when the sounding-boards of two musical instruments are connected together by a rod of pine wood, a tune played on one will be faithfully reproduced by the other. This only answers, however, for telephoning musical sounds to short distances. Another and somewhat similar example is furnished by what has been variously designated as the "string," Mechan"toy," "lovers," and "mechanical " telephone. kal teleTwo disks of thin metal, or two stretched membranes, phone. each furnished with a mouthpiece, are connected together by a thin string or wire attached at each end to the centres of the membranes. A good example may be made with two cylindrical tin cups; the bottoms form the membranes and the cups the mouthpieces. When the connecting string is held taut and sounds, such as those of ordinary speech, are produced in front of one of the membranes, pulses corresponding to the fluctuations of the atmospheric pressure are transmitted along the string and communicated to the other membrane, which in its turn communicates them to the air, thus reproducing the sound. In both these examples all the three characteristics-pitch, relative intensity, and quality-of sound are reproduced.

dis

covery.

In July 1837 Dr C. G. Page of Salem, Mass., drew attention to the sound given out by an electromagnet at the instant when the electric circuit is closed or broken, and in October Page's of the same year he discussed, in a short article entitled "Galvanic Music," the musical note produced by rapidly revolving the armature of an electromagnet in front of the poles. Experiments bearing on this subject were subsequently made by a great number of investigators. Page's discovery is of considerable importance in connexion with the theory of action of various forms of telephone, and was a very important feature in the early attempts by Reis to transit music and speech. On the 26th of August 1854 there appeared in L'Illustration (Paris) an interesting article by Charles Bourseul on the electric transmission of speech. The writer recommended the use of a flexible plate at the source of sound, which would vibrate in response to the varying pressure of the air, and thus open and close an electric circuit, and of a similar plate at the receiving station, which would be acted on electromagnetically and thus give out as many pulsations as there are breaks in the current. These suggestions were to some extent an anticipation of the work of Reis; but the conditions to be fulfilled before the sounds given out at the receiving station can be similar in pitch, quality and relative intensity to those produced at the transmitting station are not stated, and do not seem to have been appreciated.

Bour

seur's.

sugges tions.

Reis's

In Reis's lecture an apparatus was described which has given rise to much discussion as to priority in the invention of the telephone. The instrument was described in over fifty publications in various countries, and was well teleknown to physicists previous to Bell's introduction phone. of the electric telephone as a competitor with the electric telegraph. Reis caused a membrane to open and close an electric 2.See his Scientific Papers, p. 47:

'See Silliman's Jour., xxxii. 396, and xxxiii. 118.

Marrian, Phil. Mag., 3rd ser., vol. xxv. p. 382; Beatson, Arch. also Phil. Mag., 3rd ser., vol. xxxv. p. 422, and Comp. Rend., xx. de l'Elect., v. 197; De la Rive, Treatise on Electricity, i. 306; 1287. xxii. 432; Matteucci, Arch. de l'Elect., v. 389; Guillemin, Comp. Rend., xxii. 264: Wertheim, Comp. Rend., xxii. 336, 544, xxvi. 505, also Ann. de Chim. et de Phys., xxiii. 302, and Phil. Mag., 3rd ser.. vol. xxviii. p. 544: Jannair, Comp. Rend., xxiii. 319: Joule, Phil. Mag., 3rd ser., vol. xxv. pp. 76, 225; Laborde, Comp. Rend., 1. 692; Poggendorff, Pogg. Ann., Ixxxvii. 139, xcviii. 198; Du Moncel, Exp. de l'Elect., ii. 125, iii. 83; and Delesenne, Bibl. Univ. (1841), xvi. 406.

See also Didaskalia: Blätter für Geist, Gemüth, u. Publicitat, Frankfort, No. 232, 28th September 1854; Du Moncel, Exposé des Applications de l'Electricité (Paris), ii. 25. ed. 1854; iii. 110, ed. 1856, and Comp. Rend., 26th November 1877.

The English reader may consult-Jour. Soc. Tel. Eng., March 1883: British Assoc. Rep., 1863: Civ. Eng. and Arch. Jour., xxvi. 307; R. M. Ferguson, Electricity (London, 1866), p. 257: S. P. Thompson, Philipp Reis, the Inventor of the Telephone (London, 1883).

The transmitter (fig. 4), in an early form, consisted of a cell of insulating material having at its bottom a flat-headed platinum screw G; on the top of G was a layer of carbon powder Ĉ, on the top of that a platinum disk D, and above that again, forming the cover of the cell, a disk of ivory B, held in position by a ring E. Resting on the centre of the ivory disk was a small piece of rubber tubing, and this was lightly pressed by the diaphragm A, which was held in place by the mouthpiece M. The varying pressure on A, when a sound was produced near it, caused corresponding variations in the pressure on the carbon powder, and this produced similar variations in its electric resistance.

Elisha Gray's experi ments.

Experiments very similar to these of Edison were made by Elisha Gray of Boston, Mass., and described by him in papers communicated to the American Electrical Society in 1875 and 1878. In these experiments the electric current passed through the fingers of the operator's hand, which thus took the place of the spring in Edison's apparatus. The diaphragm was itself used as the rubbing surface, and it was either mounted and rotated or the fingers were moved over it. When the current passed, the friction was felt to increase, and the effect of sending a rapidly undulating current through the arrangement was to produce a sound. The application of this apparatus to the transmission of music was described by Gray.1

Dolbear's condenser telephone.

In another form of telephone, brought prominently forward by Professor A. E. Dolbear, the effects were produced by electrostatic instead of electromagnetic forces, as in the Bell telephone. Sir W. Thomson (Lord Kelvin) observed in 18633 that when a condenser is charged or discharged, a sharp click is heard, and a similar observation was made by Cromwell F. Varley, who proposed to make use of it in a telegraphic receiving instrument. In Dolbear's instrument one plate of a condenser was a flexible diaphragm, connected with the telephone line in such a way that the varying electric potential produced by the action of the transmitting telephone caused an increased or diminished charge in the condenser. This alteration of charge caused a corresponding change in the mutual attraction of the plates of the condenser; hence the flexible plate was made to copy the vibrations of the diaphragm of the transmitter. It is obvious that this apparatus might be used either as a transmitter or as a receiver, but that the effects must under ordinary circumstances be in either case extremely feeble.

It was very early recognized-and, indeed, is mentioned in the first patents of Bell, and in a caveat filed by Elisha Gray

in the United States patent office only some two Liquid hours after Bell's application for a patent-that transmitters sounds and spoken words might be transmitted to a of Bell distance by causing the vibrations of a diaphragm to and E. vary the resistance in the circuit. Both Bell and Gray Gray. proposed to do this by introducing a column of liquid into the circuit, the length or the resistance of which could be varied by causing the vibrations of the diaphragm to vary the depth of immersion of a light rod fixed to it and dipping into the liquid.

Berliner's micro

phone transmitter.

On the 4th of April 1877 Emile Berliner filed a caveat in the United States patent office, in which he stated that, on the principle of the variation with pressure of the resistance at the contact of two conductors, he had made an instrument which could be used as a telephone transmitter, and that, in consequence of the mutual forces between the two parts of the current on the two sides of the point of contact, the instrument was capable of acting as a receiver. The caveat was illustrated by a sketch showing a diaphragm with a metal patch in the 1 See George B. Prescott, The Speaking Telephone (London, 1879), pp. 151-205. Scientific American, 18th June 1881. Electrostatics and Magnetism, p. 236. 'See Tel. Journ., 1st August 1877, p. 178; also Adams, Journ. Soc. Tel. Eng., 1877, p. 476.

Edison's micro

phone

trans.

Almost simultaneously with Berliner, Edison conceived the idea of using a variable resistance transmitter. He proposed to introduce into the circuit a cell containing carbon powder, the pressure on which could be varied by the vibrations of a diaphragm. He sometimes held the carbon powder against the diaphragm in a small mitter. shallow cell (from a quarter to half an inch in diameter and about an eighth of an inch deep), and sometimes he used what he describes as a fluff, that is, a little brush of silk fibre with plumbago rubbed into it. In another form the plumbago powder was worked into a button cemented together with syrup and other substances. In the specification of the patent applied for on the 21st of July 1877 he showed a sketch of an instrument which consisted of a diaphragm, with a small platinum patch in the centre for an electrode, against which a hard point, made of plumbago powder cemented together with india-rubber and vulcanized, was pressed by a long spring, the pressure of the carbon against the platinum disk being adjusted by a straining screw near the base of the spring. Subsequently he filed an application for a patent in which various forms of springs and weights assisted in maintaining the contacts and otherwise improved the instrument.

Hughes's micro

phone.

In the early part of 1878 Professor D. E. Hughes, while engaged in experiments upon a Bell telephone in an electric circuit, discovered that a peculiar noise was produced whenever two hard electrodes, such as two wires, were drawn across each other, or were made to touch each other with a variable degree of firmness. Acting upon this discovery, he constructed an instrument which he called a "microphone," and which consisted essentially of two hard carbon electrodes placed in contact, with a current passing through the point of contact and a telephone included in the same circuit. One of the electrodes was attached to a sounding board capable of being vibrated by sound-waves and the other was held either by springs or weights in delicate contact with it. When the sounding board was spoken to or subjected to sound-waves, the mechanical resistance of the loose electrode, due to its weight, or the spring, or both, served to vary the pressure at the contact, and this gave to the current a form was therefore corresponding to the sound-waves, and it capable of being used as a speaking-telephone transmitter.7 The next transmitter of note was that introduced by Francis Blake, which came into wide use in the United States of America and other countries. In it the electrodes were of platinum and carbon.

To a frame F (fig. 5) was attached a diaphragm D of thin sheet iron; in front of this was a cover M, M provided with a suitable cavity for directing the sound-waves against the diaphragm. The microphonic arrangement consisted of a spring S, about the hundredth of an inch thick and the eighth of an inch broad, fixed at one end to a lever L, and carrying at its free extremity a brass block W. In one side of Wa small disk C of gas carbon was in. serted, resting on the hemispherical end of a small platinum pin K, about the twentieth of an inch in diameter, held in position by a thin spring A. The pressure of the carbon on the platinum point could be adjusted by the screw N, which turned the lever about the flexible joint G. The electrical connexions of the instrument as arranged for actual use are also illustrated in the figure. The current circuit went through S, W, C, K, A, and the primary circuit of the induction coil I to the battery B, and thence to S again. This formed a local circuit at the transmitting station. The line of circuit passed through the secondary of the induction coil I to the line, from that to the telephone T at the receiving station,

See Journal of the Telegraph, New York, April 1877; Philadelphia Times, 9th July 1877; and Scientific American, August 1877. This term was used by Wheatstone in 1827 for an acoustic apparatus intended to convert very feeble into audible sounds; see his Scientific Papers, p. 32.

7 See Proc. Roy. Soc., xxvii. 362; Proc. Phys. Soc., ii. 255; Phil. Mag., 5th ser., vol. vi. p. 44; W. H. Preece, Journ. Soc. Tel. Eng., vii. 270.