« EelmineJätka »
Els the second rowel-symbol and the fifth letter in our alphabet In its original form among the Phoenicians it represented the rough breathing—our h: we have seen that A represented the smooth breathing. • As the Greeks had the sound A at a very early period, it might have been expected that this symbol would have been taken by them with its original value. But the want of symbols to denote the vowels was apparently felt to be more imperative; therefore all the Phoenician symbols (corresponding to the Hebrew aleph, he, ayin) were taken to denote the vowelsounds a, e, o respectively. The form of the symbol £ has varied little from the earliest Greek times to our own. In old Latin it is sometimes, but rarely, found in the form 11. The typical sound of £ in almost all languages is one of those which we denote generally by a in English, e.g., in the word fate—that is, one of the simple'sounds between A (English ah) and I (English «), which are produced by raising the tongue gradually from its lowest position (at A) to its highest position (at I) : in this scale of sounds the lips are not employed. The most clearly distinguished of these sounds are (1) that in men, (2) that in fair, (3) that in fate. It will be observed that these sounds have here different symbols; ond if these were consistently employed in English we should not have much reason to complain of our spelling; but c has also the Isound in here and tee; at in wait has the same sound as a in fate ; and a has many sounds. Other languages employ diacritical marks to distinguish these sounds; thus in Italian we have i and e, called " open " and "close " « respectively; these correspond very nearly to (2) and (3) mentioned above. It u probable that the same distinction of sound was given in Latin by employing 04 to express the open <: at least open e is commonly found in Italian words which were written in Latin with ae, or with e short. It is possible that in Greece a similar distinction of close open e was expressed in early times by the symbols < (epsilon) and 17 (eta); but in Attica, at least after 403 B.C., the distinction seems to have been rather quantitative than qualitative. For the history of eta see article E. It is clear that in a perfect alphabet we ought to have at least three distinct symbols between A and I: we ought not to be compelled to distinguish the simple sounds by diphthongs or other modifications. Indeed yet more symbols would be desirable, for there are other sounds in this scale, which, however, are not easily distinguished from the above except by a practised ear.
It is probable that ee in English of the 16th and 17th centuries had the sound still heard in Scotland in words like ell, i.e., the simple e in our men pronounced long: < this is not unlike the open e, but the back of the tongue is lower. But M had acquired its present I sound in the last century.
EACHARD, John (1636-1697), an English divine, was born in Suffolk in 1636, and was educated at Catherine Hall, Cambridge, of which he became master in 1675 in succession to Light foot He was created a doctor of divinity in 1676 by royal mandate, and was twice (in 1679 and 1695) vice-chancellor of the university. He died on the 7th July 1697. In 1670 he had published anonymously a humorous satire entitled The Ground and Occasions of the Contempt of the Clergy enquired into in a letter to R. A, which excited much attention and provoked several replies, one of them being from John Owen. These were met by Some Observations, etc, in a second letter to B. L. (1671), written in the some bantering tone as the
original work Eochard attributed the contempt into which the clergy had fallen to their imperfect education, their insufficient incomes, and the want of a true vocation. He gave amusing illustrations of the absurdity and poverty of the current pulpit oratory of his day, some of them being taken from the sermons of his own father. He attacked the philosophy of Hobbes in his Mr JBobbs's State of Nature considered; in a dialogue between Philautus and Timothy (1672), and in his Some Opinions of Mr Hobbs considered m a second dialogue (1673). These were written in their author's chosen vein of light satire, and Dryden praised them as highly effective within their own range. It is noteworthy that Eachard's own sermons were not superior to those he satirized. Swift alludes to him as a signal instance of a successful humorist who entirely failed as a serious writer. A collected edition of his works in three volumes, with a notice of his life, was published in 1774.
EADIE, John (1810-1876), theologian and biblical critic, was born at Alva, in Stirlingshire, on the 9th May 1810. Having manifested unusual ability at school, he was sent to the university of Glasgow, where he passed through the usual curriculum in arts. Immediately afterwards he commenced to «tudy for the ministry at the Divinity Hall of the Secession Church, a dissenting body which, on its union a few years later wjth the Belief Church, adopted the denomination United Presbyterian. In 1835 he was ordained to the pastoral charge of the Cambridge Street Secession church in Glasgow. Here he speedily attained a position of great eminence and usefulness, and for many years before the close of his life he was generally regarded as the leading representative of his denomination in the city which has always been its stronghold. Though he had little claim to be called eloquent, and his style was often slovenly, he had many of the other qualities that secure the most useful and enduring kind of popularity. As a preacher he was distinguished by invariable good sense, frequent flashes of happy illustration., masculine piety, deep spiritual earnestness, breadth of sympathy both intellectual and emotional, and—most specifically of all—by the power he had in his expository discourses of conveying the best results of biblical criticism in an intelligible form to a general audience. Behind the carelessness and apparent indifference of his manner, it was not difficult to detect the quick sensibility and tender feeling which were eminently characteristic of the man. Though more than once invited to an important charge elsewhere, Dr Eadie refused to leave Glasgow, in which he found a sphere more exactly suited to his pastoral gifts than he could expect in any other place. In 1863 he removed with a portion of his congregation to a new and beautiful church at Lansdowne Crescent, where his influence continued unabated until his death.
From his student days Eadie bore a reputation for extensive, if not profound and accurate, scholarship, which he justified and increased during the earlier years of his ministry to such an extent that in 1843 the church to which he belonged appointed him professor of biblical literature and hermeneutics in its Divinity Hall He held this appointment along with his ministerial charge till the close of his life, and discharged its duties with an efficiency that was universally acknowledged. While his scholarship was not minute or thorough, he was surpassed by few biblical commentators of his day in range of learning, and by still' fewer in the soundness of judgment with which his learning was applied. As a critic he was acute and painstaking;
as an interpreter lie was eminently fair-minded. In the professor's chair, as in the pulpit, his strength lay in the tact with which he selected the soundest results of biblical criticism, whether his own or that of others, and presented them in a clear and connected form, with a constant view to their practical bearing. If this last fact gave a nonacademic aspect to some portions of his lectures, it rendered them not less interesting and probably not less useful to his auditors. Eadie's merits as a scholar were early acknowledged by the usual honorary university distinctions. He received the degree of LL.D. from Glasgow in 1844, and that of D.D. from St Andrews in 1850.
Busily engaged as he was in two distinct offices, either of which might well of itself have employed all his energies, Eadie nevertheless found time for an amount of work in a third sphere, of which the same thing might be said. His labours as an author would have been more than creditable to one who had no other occupation. Host of his works were connected with biblical criticism and interpretation, some of them being designed for popular use and others being more strictly scientific To the former class belong the Biblical Cyclopcedia, his edition of Cruden't Concordance, his Early Oriental History, and his discourses on The Divine Love and on Paul the Preacher ; to the latter belong his commentaries on the Greek text of St Paul's epistles to the Ephesian3, Colossians, Philippians, and Galatians, published at intervals in four volumes, which take a high rank among exegetical works. His Life of Dr Kitto obtained a deserved popularity. His last work, the History of the English Bible (2 vols. 1876), will probably be the most enduring memorial of his ability as an author. Though not unimpeachable in point of arrangement and style, it contains a fuller and more accurate account of the subject than is to be found anywhere else, and almost every page bears marks of the life-long interest and loving research of the author. His almost unrivalled knowledge of the various English versions, as well as his ability as a critic and interpreter of the original, led to his being selected as one of the company for the revision of the Authorized version of the New Testament, and in this capacity it is understood that he rendered excellent service. Dr Eadie died at Glasgow on the 3d June 1876.
EADMER, or Edmeb (in Latin Eadmerus, and by mistake Edimerus and Edinerus), an English ecclesiastic and historian of the Norman period, probably, as his name suggests, of English as opposed to Norman parentage At an early age he was sent to the Benedictine monastery at Canterbury ; and there he became acquainted with Ansehn, at the time of the latter's first visit to England as abbot of Bee. The intimacy was renewed when Anselm was raised to the episcopal see; and thenceforward Eadmer was not so much the archbishop's disciple and follower as his friend and director, and that at last not only by Anselm's private recognition, but by the formal appointment of Pope Urban IL So complete, indeed, was the obedionce shown by the great scholastic philosopher and head of the English Church to his self-elected tutor, that—according to William of Malmesbury, De geslis pontificum Anglorum, lib. i.—he is said to have waited for his express permission before he rose from his bed, or even turned from one side to the other. After Anselm's death Eadmer accompanied Radulpb, the new archbishop, to Rome in 1119; and on their return in 1120 he was nominated to the see of St Andrews in Scotland. Owing, however, to the refusal of the S.cotch to recognize the claims put forward by Eadmer and his patron in support of the episcopal authority of the see of Canterbury, he was never formally inducted into the office. He was at Canterbury in 1121, and he spent the latter part of his life as prior of the monastery there. His death is variously assigned to the year 1123 and 1137.
Eadmer has loft a large number of works, of which a list is given in Wharton's Anglia Sacra, part ii. Most important an his Historia Nnorum, in six books treating of his own times down to the death of Badulph in 1122, and nis Vita Aneelmi, which ranks as one of the chief authorities in regard to the primate. The former was first published by Selden m 1623, the hitter at Antwerp in 1651; and both have since been several times reprinted. Of less mark are his lives of Odo, Bregwin, and Duns tan, and of Oswald and Wilfrid of York, and his treatises—formerly ascribed to Anselm—Dc quatuor virtutibiis quae fucrtmt in bcata Maria virgine, and De Similittutinibve 8. Aneelmi. Nearly all his works are to be found in an early MS. in the library of Corpus Christi College, Cambridge (C.C.C.C., No 871), and most of them have been reprinted as an appendix to Anselm's Opera by Gerberon, foL 1675, and by the Benedictine monks of St Maine, foL Paris, 1721. A number of his letters are preserved in MSS. Cotton., Otho, A. xii.
See especially Wright, Bioerapkia Brit. Lit., Anglo-Norman Period, 1848; Charma, Satnl Anulm, 1833, pp. 186,187; Burton, liutot? »/ Scotland, Tol. L pp. 422-424.
EAGLE (French Aigle, from the Latin Aqvila), the name generally given to the larger Diurnal Birds-of-prey which are not Vultures; but tne limits of the subfamily Agvilince have been very variously assigned by different writers on systematic ornithology, and, as before observed (b^zzasd, vol iv. p. 60}), there are Eagles smaller than certain Buzzards. By some authorities the Loemmergeier of the Alps, and other high mountains of Europe, North Africa, and Asia, is accounted an Eagle, but by others the genus Gypaelus is placed with the Vulturidce, as its common English name (Bearded Vulture) shows. There are also other forms, such as the South-American Harpyia and its allies, which though generally called Eagles have been ranked as Buzzards. In the absence of any truly scientific definition of the family Aquilina it is best to leave these and many other more or less questionable members of the group—-such as the genera Spuaetui, Circaetits) Spilornia, Helotarsus, and so forth—and, so far as space will allow, to treat here of those whose position cannot be gainsaid.
True Eagles inhabit all the Regions of the world, and some seven or eight species at least are found in Europe, of which two are resident in the British Islands. In England and in the Lowlands of Scotland Eagles only exist as stragglers; but in the Hebrides and some parts of the Highlands a good many may yet be found, and their numbers appear to have rather increased of late years than diminished; for the foresters and shepherds, finding that a 'high price can be got for their eggs, take care to protect the owners of the eyries, which are nearly all well known, and to keep up the stock by allowing them at times to rear their young. There are also now not a few occupiers of Scottish forests who interfere so far as they can to protect the king of birds. But hardly twenty years ago trapping, poisoning, and other destructive devices were resorted to without stint, and there was then every probability that before long not an Eagle would be left to add the wild majesty of its appearance to the associations of the mountain or the lake.1 In Ireland the extirpation of Eagles seems to have been carried on almost unaffected by the prudent considerations which in the northern kingdom have operated so favourably for the race, and except in the wildest parts of Donegal, Mayo, and Kerry, Eagles in the sister-island are said to be almost birds of the past.
Of the two British species the Erne (Iceh (Ern) or Sea
1 The late Lord Breadalbane was perhaps the first large landowner who set the example that has been sinco followed by others. On hia unrivalled forest of Black Mount, Eagles—elsewhere persecuted to the death—were by him ordered to be unmolested so long as they were not numerous enough to cause considerable depredations on the fanners'flocks. Hethought, and all who have an eye for the harmonies of nature will agree with him, that the spectacle of a soaring Eagle was a fitting adjunct to the grandeur of his Argyllshire mountainscenery, and a good equivalent for the occasional loss of a lamb, or the alight deduction from the Tent paid by his tenantry in consequence. How faithfully his wishes were carried out by his head-forester, Mr Peter Robertson, the present writer has abimdant means of knowing.
yearly do, and appear in England. The adults (fig. 1) are distinguished by their prevalent greyish-brown colour, their pale head, yellow beak, and white tail—characters, however, wanting in the immature, which do not assume the perfect plumago for some three or four years. The eyry is commonly placed in a high cliff or on an island in a lake— sometimes on the ground, at others in a tree—and consists of a vast mass of sticks, in the midst of which is formed a hollow lined with Luzula sylvatica (as first observed by the late Mr John Wolley) or some similar grass, and here arelaid tho two or three white eggs. In former days the SeaEagle seems to have bred in several parts of England—as the Lake district, and possibly even in the Isle of Wight and on Dartmoor. This species inhabits all the northern part of the Old World from Iceland to Kamchatka, and breeds in Europe so far to the southward as Albania. In the New World, however, it is only found in Greenland, being elsewhere replaced by the White-headed or Bald Eagle, H. leucocephalus, a bird of similar habits, and tho chosen emblem of the United States of America. In the far east of Asia occurs a still larger and finer Sea-Eagle, H. pdagicus, remarkable for its white thighs and upper wingcjverts. South-eastern Europe and India furnish a much smaller species, H. leucoryphus, which has its representative, B. leucogaster, in the Malay Archipelago and Australia, and, as allies in South Africa and Madagascar, H. vocifer and H. vociferoida respectively. All these Eagles may be distinguished by their scaly tarsi, while the group next to lie treated of have the tarsi feathered to the toes.
The Golden or Mountain-Eagle, Aquila chryiartus, is the second British species. This also formerly inhabited England, and a nest, found in 1668 in the Peak of Derby
neighbourhood of water is not requisite. The eggs, from two to four in number, vary from a pure white to a mottled, and often highly-coloured, surface, on which appear different shades of red and purple. The adult bird (fig. 2) is of a rich, dark brown, with the elongated feathers of the neck, especially on the nape, light tawny, in which imagination sees a "golden" hue, and the tail marbled with brown and ashy-grey. In the young the tail is white at the base, and the neck has scarcely any tawny tint The Golden Eagle does not occur in Iceland, but occupies suitable situations over the rest of the Paloearctic Region and a considerable portion of the Nearctic—though the Amencan bird has been, by some, considered a distinct species. Domesticated, it has many times been trained to take prey for its master in Europe, and to this species is thought to belong an Eagle habitually used by the Kirgii Tartars, who call it Bergut or Searcoot, for the capture of antelopes, foxes, and wolves. It is carried hooded on horseback or on a perch between two men, and released when the quarry is in sight. Such a bird, when well trained, is valued, says Pallas, at the price of two camels. It is quite possible, however, that more than one kind of Eagle is thus used, and the services of A. hthaca (which is tho Imperial Eagle of some writers') and of A. mogUnik—
1 As already stated, the site chosen varies greatly. Occasionally placed in a niche in what passes for a perpendicular cliff to which access conld only be gained by a skilful cragsman with a rope, the Titer has known a nest to within ten or fifteen yards of which he rode on a pony. Two beautiful views of as many Golden Eagle's nests, drawn on the spot by Mr "Wolf, are given in tho OoUuta IVrtleyana, and a fine series of eggs is also figured in the same work.
* Which species may havo been the tradition*! emblem of Roiaas power, and tho A Us Jovist la Yery uncertain.
both of which are found in Central Asia, as well as in South-eastern Europe—may also be employed.
Of the other more or less nearly allied species or races want of room forbids the consideration, but there is a smaller form on which a few words may be said. This has usually gone under the name of A. navia, but is now thought by the best authorities to include three local races, or, in the eyes of some, species. They inhabit Europe, North Africa, and Western Asia to India, and two examples of one of them—A. donga, the form which is somewhat plentiful in North-eastern Germany—have occurred in Cornwall The smallest true Eagle is A. pennata, which inhabits Southern Europe, Africa, and India, Differing from other Eagles, of their genus by its wedgeshaped tail, though otherwise greatly resembling them, is the A. audax of Australia. Lastly may be noticed here a small group of Eagles, characterized by their long legs, forming the genus Nisaetus, of which one species, N. fasciatus, is found in Europe. The Osprey (Pandion), though placed by many among the Aquilince, certainly docs not belong to that subfamily. (a. N.)
EAR The simplest form of the organ of hearing is a small sac containing fluid, with the auditory nerve expanded upon it. Sonorous vibrations are communicated to this sac either directly through the hard parts of the head, or at the same time by a membrane exposed to the surroundiag medium. • Such is the form of ear found in many of the Crustacea and in the Cephalopoda. In the Vertebrata,. there is a progressive development and increasing complexity from tho fishes up to Mammalia. For details as to' the structure of the ear in the different subdivisions of the Vertebrata, reference is made to the articles treating of these, such as Amphibia, Birds, cfec. ; and the structure of the human ear will be found fully described in the article Anatomy, vol. i. p. 891. It is the object of this article to describe the phenomena of auditory sensation from the physiological point of view.
The sense of hearing is a rpecial sensation the causo of which is an excitation of the auditory nerves by the vibrations of sonorous bodies. A description of sonorous vibrations and of their transmission is given in the article Acoustics; here we shall consider, first, the transmission of such vibrations from the external ear to the auditory nerve, and secondly, the physiological characters of auditory sensation.
L—1. Transmission in External Ear.—The external ear consists of the pmno, or auricle, and the external auditory meatus, or canal, at the bottom of which we find the fnembrana 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, has not caused 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 must 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 a kind of air-tube between the pharynx and the tympanum for the purpose of regulating pressure on the membrana tympani. It is generally supposed that during rest the tube is open, and that 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 may occur within certain limits, as 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, tho membrana tympani will bulge outwards, in the second case inwards, and in both, from excessive stretching of the membrane, thero 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 tho membrane after an external vibration has ceased, so that a sound is not heard much longer than it 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, or in a pathological condition, 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, according to Helmholtz, 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 own elasticity and by tho elasticity of the chain of bones. This power of varying the tension of the membrane is a kind of 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 tho membrane is tense, it will readily respond to high sounds, while relaxation will be the condition most adapted for low sounds. 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.
Helmholtz has also pointed out that the peculiar form of the membrana tympani in man has the effect of increasing the force of its vibrations at the expense of their amplitude.
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 ths malleus, incus, and stapes. Of these, transmission by the chain of bones is by far the most important. In birds and in the scaly 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—aro connected by a compound lever consisting of three bones, namely, the malleus, or hammer, inserted into the membrana tympani, the incut, or anvil, and the stapes, or stirrup, the base of which fits into the oval window. The lever thus formed has its fulcrum near the short process of the incus, which abuts against the tympanic wall; the power is applied at the handle of the malleus, and the resistance is at the base of the stirriip. Both by direct experimental observation and by calculation from data supplied by measurement of the lengths of the arms of the lever, Helmholtz has shown that by this arrangement vibrations are diminished in extent in the ratio of 3 to 2, but are inversely increased in force. Considering the great resistance offered to excursions of the stapea, such an arrangement must bo advantageous. 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 small fraction of the wave length of the sound transmitted.
3. Transmission in the Internal Ear.—The internal car 13 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 (Bee voL i. p. 893). The osseous labyrinth may be regarded as an osseous mould in the petrous portion of the temporal bone, lined by tessclated 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 connection with the auditory nerve, immersed in another fluid called the endolymph. The membranous labyrinth consists of a vestibular portion formed by two small saclike 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 ccoustica, there are cells bearing or developed into long auditory hairs, which are to be regarded as 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 vestib ali, because it commences in the vestibule, and the scala tympani, because it ends in the tympanum, at the round window. These two scabs communicate at the apex of the cochlea, The roof of the ductus cochlearis is formed by a thin membrane called the membrane of Reistner, while its floor consists of the basilar membrane, on which we find the remarkable organ of Corti, which constitutes the terminal organ of the ochloar division of ihe auditory
nerve, and which is fully described in vol. i. p. 891. It it 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 be supposed to act as a damping apparatus, so as quickly to stop their movements. The ductus cochlearis and the two scala; are filled with fluid. Sonorous vibrations maf 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 peculiar 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 has not been satisfactorily made out to what extent, if any, vibrations may be communicated to the fluid in the labyrinth by the round window. There can be no doubt, however, that in ordinary hearing vibrations are communicated chiefly by the chain of bones. When the base of the stirrup is pushed into the oval window, the pressure in the labyrinth increases, the impulse passes along the scala vestibuli to the scala tympani, 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 tba Btirrup passes outwards, a reverse action takes place. Thus the fluid of the labyrinth may receive a series of pulses or vibrations isochronous with the movements of the base of tho stirrup, and these pulses' affect the terminal apparatus in connection with the auditory nerve.
Since the size of the membranous labyrinth is so small, measuring, in man, not more than A inch in length by |th inch 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 Beissner, 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 whan we take into account the fact that impulses aro 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. 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: if too feeble, no impression will be produced. The minimum limit has been stated to be the sensation caused by the falling of a ball of pith, 1 millegramme in weight, upon a smooth surface, such as glass, from a height of 1 millimetre at a distance of 91 millimetres from the ear.