Part 1

# Encyclopaedia Britannica, 11th Edition, "Hearing" to "Helmond": Volume 13, Slice 2 ### By Various

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Produced by Marius Masi, Don Kretz and the Online Distributed Proofreading Team at http://www.pgdp.net

Transcriber's notes:

(1) Numbers following letters (without space) like C2 were originally printed in subscript. Letter subscripts are preceded by an underscore, like C_n.

(2) Characters following a carat (^) were printed in superscript.

(3) Side-notes were relocated to function as titles of their respective paragraphs.

(4) Macrons and breves above letters and dots below letters were not inserted.

(5) [root] stands for the root symbol; [alpha], [beta], etc. for greek letters.

(6) The following typographical errors have been corrected:

ARTICLE HEAT: "This line of reasoning does not appear quite satisfactory, because it is tacitly assumed, in the reasoning by which Carnot's principle was established, ..." 'tacitly' amended from 'tactitly'.

ARTICLE HEBREWS, EPISTLE TO THE: "Clement himself, taking it for granted that an epistle to Hebrews must have been written in Hebrew, supposes that Luke translated it for the Greeks." 'been' amended from 'beeen'.

ARTICLE HEBRIDES, THE: "The United Free Church has a strong hold on the people, but in a few of the islands the Roman Catholics have a great following." 'people' amended feom 'poeple'.

ARTICLE HEBRIDES, THE: "A new system of management and high rents was imposed, in consequence of which numbers of the tacksmen, or large tenants, emigrated to North America." 'was' amended from 'were'.

ARTICLE HEBRON: "It is an enclosure measuring 112 ft. east and west by 198 north and south, surrounded with high rampart walls of masonry similar in size and dressing to that of the Jerusalem Haram walls." 'similar' amended from 'similiar'.

ARTICLE HEINE, HEINRICH: "... the beginning of a new era in German journalism and a healthy revolt against the unwieldy prose of the Romantic period." 'unwieldy' amended from 'unwieldly'.

ARTICLE HELIOMETER: "The reader is referred to that paper for an exhaustive history and discussion of the instrument." 'instrument' amended from 'intrument'.

ARTICLE HELIUM: "M. Travers, G. Senter and A. Jacquerod (Phil. Trans. A. 1903, 200, p. 105) carefully examined the behaviour of a constant volume gas thermometer filled with helium." 'behaviour' amended from 'behavour'.

ARTICLE HELLENISM: "It has even been thought that some developments of the Egyptian religion are due to Hellenistic influence, ..." 'Egyptian' amended from 'Egyptain'.

ENCYCLOPAEDIA BRITANNICA

A DICTIONARY OF ARTS, SCIENCES, LITERATURE AND GENERAL INFORMATION

ELEVENTH EDITION

VOLUME XIII, SLICE II

HEARING to HELMOND

ARTICLES IN THIS SLICE:

HEARING HEIDEGGER, JOHANN HEINRICH HEARN, LAFCADIO HEIDELBERG (town of Germany) HEARNE, SAMUEL HEIDELBERG (town of Transvaal) HEARNE, THOMAS HEIDELBERG CATECHISM, THE HEARSE HEIDELOFF, KARL ALEXANDER VON HEART HEIDENHEIM HEART-BURIAL HEIFER HEARTH HEIGEL, KARL AUGUST VON HEARTS HEIJERMANS, HERMANN HEAT HEILBRONN HEATH, BENJAMIN HEILIGENSTADT HEATH, NICHOLAS HEILSBERG HEATH, WILLIAM HEILSBRONN HEATH HEIM, ALBERT VON ST GALLEN HEATHCOAT, JOHN HEIM, FRANCOIS JOSEPH HEATHCOTE, SIR GILBERT HEIMDAL HEATHEN HEINE, HEINRICH HEATHFIELD, GEORGE ELIOTT HEINECCIUS, JOHANN GOTTLIEB HEATING HEINECKEN, CHRISTIAN HEINRICH HEAVEN HEINICKE, SAMUEL HEBBEL, CHRISTIAN FRIEDRICH HEINSE, JOHANN JAKOB WILHELM HEBBURN HEINSIUS, DANIEL HEBDEN BRIDGE HEINSIUS, NIKOLAES HEBE HEIR HEBEL, JOHANN PETER HEIRLOOM HEBER, REGINALD HEJAZ HEBER, RICHARD HEJIRA HEBERDEN, WILLIAM HEL HEBERT, EDMOND HELDENBUCH, DAS HEBERT, JACQUES RENE HELDER HEBREW LANGUAGE HELEN HEBREW LITERATURE HELENA, ST HEBREW RELIGION HELENA (Arkansas, U.S.A.) HEBREWS, EPISTLE TO THE HELENA (Montana, U.S.A.) HEBRIDES, THE HELENSBURGH HEBRON HELENUS HECATAEUS OF ABDERA HELGAUD HECATAEUS OF MILETUS HELGESEN, POVL HECATE HELIACAL HECATOMB HELIAND HECATO OF RHODES HELICON (mountain range) HECKER, FRIEDRICH FRANZ KARL HELICON (contrabass tuba) HECKER, ISAAC THOMAS HELIGOLAND HECKMONDWIKE HELIOCENTRIC HECTOR HELIODORUS HECUBA HELIOGABALUS (ELAGABALUS) HEDA, WILLEM CLAASZ HELIOGRAPH HEDDLE, MATTHEW FORSTER HELIOMETER HEDGEHOG HELIOPOLIS HEDGES AND FENCES HELIOSTAT HEDON HELIOTROPE HEDONISM HELIOZOA HEEL HELIUM HEEM, JAN DAVIDSZ VAN HELIX HEEMSKERK, JOHAN VAN HELL HEEMSKERK, MARTIN JACOBSZ HELLANICUS HEER, OSWALD HELLEBORE HEEREN, ARNOLD HERMANN LUDWIG HELLENISM HEFELE, KARL JOSEF VON HELLER, STEPHEN HEGEL, GEORG WILHELM FRIEDRICH HELLESPONT HEGEMON OF THASOS HELLEVOETSLUIS HEGEMONY HELLIN HEGESIAS OF MAGNESIA HELLO, ERNEST HEGESIPPUS (Athenian orator) HELMERS, JAN FREDERIK HEGESIPPUS (early Christian writer) HELMERSEN, GREGOR VON HEGESIPPUS (author of Jewish War) HELMET HEGIUS [VON HEEK], ALEXANDER HELMHOLTZ, HERMANN LUDWIG VON HEIBERG, JOHAN LUDVIG HELMOLD (historian) HEIDE HELMOND (town in Holland)

HEARING (formed from the verb "to hear," O. Eng. _hyran_, _heran_, &c., a common Teutonic verb; cf. Ger. _horen_, Dutch _hooren_, &c.; the O. Teut. form is seen in Goth. _hausjan_; the initial _h_ makes any connexion with "ear," Lat. _audire_, or Gr. [Greek: akouein] very doubtful), in physiology, the function of the ear (q.v.), and the general term for the sense or special sensation, the cause of which is an excitation of the auditory nerves by the vibrations of sonorous bodies. The anatomy of the ear is described in the separate article on that organ. A description of sonorous vibrations is given in the article SOUND; here we shall consider the transmission of such vibrations from the external ear to the auditory nerve, and the physiological characters of auditory sensation.

1. _Transmission in External Ear._--The external ear consists of the _pinna_, or auricle, and the _external auditory meatus_, or canal, at the bottom of which we find the _membrana tympani_, or drum head. In many animals the auricle is trumpet-shaped, and, being freely movable by muscles, serves to collect sonorous waves coming from various directions. The auricle of the human ear presents many irregularities of surface. If these irregularities are abolished by filling them up with a soft material such as wax or oil, leaving the entrance to the canal free, experiment shows that the intensity of sounds is weakened, and that there is more difficulty in judging of their direction. When waves of sound strike the auricle, they are partly reflected outwards, while the remainder, impinging at various angles, undergo a number of reflections so as to be directed into the auditory canal. Vibrations are transmitted along the auditory canal, partly by the air it contains and

## partly by its walls, to the membrana tympani. The absence of the

auricle, as the result of accident or injury, does not cause diminution of hearing. In the auditory canal waves of sound are reflected from side to side until they reach the membrana tympani. From the obliquity in position and peculiar curvature of this membrane, most of the waves strike it nearly perpendicularly, and in the most advantageous direction.

2. _Transmission in Middle Ear._--The middle ear is a small cavity, the walls of which are rigid with the exception of the portions consisting of the membrana tympani, and the membrane of the round window and of the apparatus filling the oval window. This cavity communicates with the pharynx by the _Eustachian tube_, which forms an air-tube between the pharynx and the tympanum for the purpose of regulating pressure on the membrana tympani. During rest the tube is open, but it is closed during the act of deglutition. As this action is frequently taking place, not only when food or drink is introduced, but when saliva is swallowed, it is evident that the pressure of the air in the tympanum will be kept in a state of equilibrium with that of the external air on the outer surface of the membrana tympani, and that thus the membrana tympani will be rendered independent of variations of atmospheric pressure such as occur when we descend in a diving bell or ascend in a balloon. By a forcible expiration, the oral and nasal cavities being closed, air may be driven into the tympanum, while a forcible inspiration (Valsalva's experiment) will draw air from that cavity. In the first case, the membrana tympani will bulge outwards, in the second case inwards, and in both, from excessive stretching of the membrane, there will be partial deafness, especially for sounds of high pitch. Permanent occlusion of the tube is one of the most common causes of deafness.

The membrana tympani is capable of being set into vibration by a sound of any pitch included in the range of perceptible sounds. It responds exactly as to number of vibrations (pitch), intensity of vibrations (intensity), and complexity of vibration (quality or timbre). Consequently we can hear a sound of any given pitch, of a certain intensity, and in its own specific timbre or quality. Generally speaking, very high tones are heard more easily than low tones of the same intensity. As the membrana tympani is not only fixed by its margin to a ring or tube of bone, but is also adherent to the handle of the malleus, which follows its movements, its vibrations meet with considerable resistance. This diminishes the intensity of its vibrations, and prevents also the continued vibration of the membrane after an external pressure has ceased, so that a sound is not heard much longer than its physical cause lasts. The tension of the membrane may be affected (1) by differences of pressure on the two surfaces of the membrana tympani, as may occur during forcible expiration or inspiration, and (2) by muscular action, due to contraction of the _tensor tympani_ muscle. This small muscle arises from the apex of the petrous temporal and the cartilage of the Eustachian tube, enters the tympanum at its anterior wall, and is inserted into the malleus near its root. The handle of the malleus is inserted between the layers of the membrana tympani, and, as the malleus and incus move round an axis passing through the neck of the malleus from before backwards, the

## action of the muscle is to pull the membrana tympani inwards towards the

tympanic cavity in the form of a cone, the meridians of which are not straight but curved, with convexity outwards. When the muscle contracts, the handle of the malleus is drawn still farther inwards, and thus a greater tension of the tympanic membrane is produced. On relaxation of the muscle, the membrane returns to its position of equilibrium by its elasticity and by the elasticity of the chain of bones. This power of varying the tension of the membrane is an accommodating mechanism for receiving and transmitting sounds of different pitch. With different degrees of tension it will respond more readily to sounds of different pitch. Thus, when the membrane is tense, it will readily respond to high sounds, while relaxation will be the condition most adapted for low tones. In addition, increased tension of the membrane, by increasing the resistance, will diminish the intensity of vibrations. This is especially the case for sounds of low pitch.

The vibrations of the membrana tympani are transmitted to the internal ear partly by the air which the middle ear or tympanum contains, and

## partly by the chain of bones, consisting of the malleus, incus and

stapes. Of these, transmission by the chain of bones is by far the most important. In birds and in the amphibia, this chain is represented by a single rod-like ossicle, the _columella_, but in man the two membranes--the membrana tympani and the membrane filling the fenestra ovalis--are connected by a compound lever consisting of three bones, namely, the _malleus_, or hammer, inserted into the membrana tympani, the _incus_, or anvil, and the _stapes_, or stirrup, the base of which is attached to a membrane covering the oval window. It must also be noted that in the transmission of vibrations of the membrana tympani to the fluid in the labyrinth or internal ear, through the oval window, the chain of ossicles vibrates as a whole and acts efficiently, although its length may be only a fraction of the wave-length of the sound transmitted. The chain is a lever in which the handle of the malleus forms the long arm, the fulcrum is where the short process of the incus abuts against the wall of the tympanum, while the long process of the incus, carrying the stapes, forms the short arm. The mechanism is a lever of the second order. Measurements show that the ratio of the lengths of the two arms is as 1.5 : 1; the ratio of the resulting force at the stapes is therefore as 1 : 1.5; while the amplitudes of the movements at the tip of the handle of the malleus and the stapes is as 1.5 : 1. Hence, while there is a diminution in amplitude there is a gain in power, and thus the pressures are conveyed with great efficiency from the membrana tympani to the labyrinth, while the amplitude of the oscillation is diminished so as to be adapted to the small capacity of the labyrinth. As the drum-head is nearly twenty times greater in area than the membrane covering the oval window, with which the base of the stapes is connected, the energy of the movements of the membrana tympani is concentrated on an area twenty times smaller; hence the pressure is increased thirtyfold (1.5 X 20) when it acts at the base of the stapes. Experiments on the human ear have shown that the movement of greatest amplitude was at the tip of the handle of the malleus, 0.76 mm.; the movement of the tip of the long arm process of the incus was 0.21 mm.; while the greatest amplitude at the base of the stapes was only .0714 mm. Other observations have shown the movements at the stapes to have a still smaller amplitude, varying from 0.001 to 0.032 mm. With tones of feeble intensity the movements must be almost infinitesimal. There may also be very minute transverse movements at the base of the stapes.

3. _Transmission in the Internal Ear._--The internal ear is composed of the labyrinth, formed of the vestibule or central part, the semicircular canals, and the cochlea, each of which consists of an osseous and a membranous portion. The osseous labyrinth may be regarded as an osseous mould in the petrous portion of the temporal bone, lined by tesselated endothelium, and containing a small quantity of fluid called the _perilymph_. In this mould, partially surrounded by, and to some extent floating in, this fluid, there is the membranous labyrinth, in certain parts of which we find the terminal apparatus in connexion with the auditory nerve, immersed in another fluid called the _endolymph_. The membranous labyrinth consists of a vestibular portion formed by two small sac-like dilatations, called the _saccule_ and the _utricle_, the latter of which communicates with the semicircular canals by five openings. Each canal consists of a tube, bulging out at each extremity so as to form the so-called _ampulla_, in which, on a projecting ridge, called the _crista acustica_, there are cells bearing long _auditory hairs_, which are the peripheral end-organs of the vestibular branches of the auditory nerve. The cochlear division of the membranous labyrinth consists of the _ductus cochlearis_, a tube of triangular form fitting in between the two cavities in the cochlea, called the _scala vestibuli_, because it commences in the vestibule, and the _scala tympani_, because it ends in the tympanum, at the round window. These two scalae communicate at the apex of the cochlea. The roof of the ductus cochlearis is formed by a thin membrane called the _membrane of Reissner_, while its floor consists of the _basilar membrane_, on which we find the remarkable _organ of Corti_, which constitutes the terminal organ of the cochlear division of the auditory nerve. It is sufficient to state here that this organ consists essentially of an arrangement of epithelial cells bearing hairs which are in communication with the terminal filaments of this portion of the auditory nerve, and that groups of these hairs pass through holes in a closely investing membrane, _membrana reticularis_, which may act as a damping apparatus, so as quickly to stop their movements. The ductus cochlearis and the two scalae are filled with fluid. Sonorous vibrations may reach the fluid in the labyrinth by three different ways--(1) by the osseous walls of the labyrinth, (2) by the air in the tympanum and the round window, and (3) by the base of the stapes inserted into the oval window.

When the head is plunged into water, or brought into direct contact with any vibrating body, vibrations must be transmitted directly. Vibrations of the air in the mouth and in the nasal passages are also communicated directly to the walls of the cranium, and thus pass to the labyrinth. In like manner, we may experience auditive sensations, such as blowing, rubbing and hissing sounds, due to muscular contraction or to the passage of blood in vessels close to the auditory organ. It is doubtful whether any vibrations are communicated to the fluid in the labyrinth by the round window. Vibrations which cause hearing are communicated by the chain of bones. When the base of the stirrup is pushed into the oval window, the pressure in the labyrinth increases, and, as the only mobile part of the wall of the labyrinth is the membrane covering the round window, this membrane is forced outwards; when the base of the stirrup moves outwards a reverse action takes place. Thus the fluid of the labyrinth receives a series of pulses isochronous with the movements of the base of the stirrup, and these pulses affect the terminal apparatus in connexion with the auditory nerve.

The sacs of the internal ear, known as the utricle and saccule, receive the impulses of the base of the stapes. They are organs connected with the perception of sounds as sounds, without reference to pitch or quality. For the _analysis_ of tone a cochlea is necessary. Even in mammals all the parts of the ear may be destroyed or affected by disease, except these sacs, without causing complete deafness.

It has been suggested by Lee (_Amer. Jour. of Physiol._ vol. i. No. 1, p. 128) that in fishes the sac has nothing to do with hearing, but serves for the perception of movements, such as those of rotation and translation through space, movements much coarser than those that form the physical basis of sound. He considers, also, that as fishes, with few exceptions, are dumb, they are also deaf. In the fish there are peculiar organs along the lateral line which are known to be connected with the perception of movements of the body as a whole, and Beard (_Zool. Anz. Leipzig_, 1884, Bd. vii. S. 140) has attempted to trace a phylogenetic connexion between the sacs of the internal ear and the organs in the lateral line. According to this view, when animals became air-breathers, a part of the ear (the _papilla acustica basilaris_) was gradually evolved for the perception of delicate vibrations of sound. (See EQUILIBRIUM.)

It is by means of the cochlea that we discriminate pitch, hear beats, and are affected by quality of tone.

Since the size of the membranous labyrinth is so small, measuring, in man, not more than 1/2 in. in length by 1/8 in. in diameter at its widest part, and since it is a chamber consisting partly of conduits of very irregular form, it is impossible to state accurately the course of vibrations transmitted to it by impulses communicated from the base of the stirrup. In the cochlea vibrations must pass from the saccule along the scala vestibuli to the apex, thus affecting the membrane of Reissner, which forms its roof; then, passing through the opening at the apex (the _helicotrema_), they must descend by the scala tympani to the round window, and affect in their passage the membrana basilaris, on which the organ of Corti is situated. From the round window impulses must be reflected backwards, but how they affect the advancing impulses is not known. But the problem is even more complex when we take into account the fact that impulses are transmitted simultaneously to the utricle and to the semicircular canals communicating with it by five openings. The mode of action of these vibrations or impulses upon the nervous terminations is still unknown; but to appreciate critically the hypothesis which has been advanced to explain it, it is necessary, in the first place, to refer to some of the general characters of auditory sensation.

4. _General Characters of Auditory Sensations._--Certain conditions are necessary for excitation of the auditory nerve sufficient to produce a sensation. In the first place, the vibrations must have a certain _amplitude_ and _energy_; if too feeble, no impression will be produced.

Various physicists have attempted to measure the sensitiveness of the ear by estimating the amplitude of the molecular movements necessary to call forth the feeblest audible sound. Thus A. Topler and L. Boltzmann, on data founded on experiments with organ pipes, state that the ear is affected by vibrations of molecules of the air not more in amplitude than .0004 mm. at the ear, or 0.1 of the wave-length of green light, and that the energy of such a vibration on the drum-head is not more than 1/543 billionth kilog., or 1/17th of that produced upon an equal surface of the retina by a single candle at the same distance (_Ann. d. Phys. u. Chem._, Leipzig. 1870, Bd. cxli. S. 321). Lord Rayleigh, by two other methods, arrived at the conclusion "that the streams of energy required to influence the eye and ear are of the same order of magnitude." He estimated the amplitude of the movement of the aerial particles, with a sound just audible, as less than the ten-millionth of a centimetre, and the energy emitted when the sound was first becoming audible, at 42.1 ergs per second. He also states that in considering the amplitude or condensation in progressive aerial waves, at a distance of 27.4 metres from a tuning-fork, the maximum condensation was = 6.0 X 10^-9 cm., a result showing "that the ear is able to recognize the addition or subtraction of densities far less than those to be found in our highest vacua" (_Proc. Roy. Soc._, 1877, vol. xxvi. p. 248; _Lond. Edin. and Dub. Phil. Mag._, 1894, vol. xxxviii. p. 366).