"3. In the perturbations of declination which I havo observed for 28 years, I have been unable to recognise any general law. 4. The perturbations of horizontal intensity commence in general by an increase of that force, and finish always by a diminu. ion, which lasts for two or three days. 5. In all perturbations there is a constant relation between changes of inclination and the simultaneous changes of horizontal intensity, such that an augmentation of intensity of corre sponds to a diminution of inclination of 8° 23 (fcr Munich). "6. In telegraphic wires we cannot observe the existence of a constant terrestrial current, since the conductivity of the soil is infinitely greater than that of the telegraphic wire, and it is only sudden changes that manifest themselves. In consequence, during magnetic perturbations in the galvanometer of a telegraphic wire, we only see irregular deflections to right or left, succeeding each other at intervals of a few minutes. "In 1850 and 1851 we made electrical observations from hour to hour, from 7 A. M. to 6 P.M., without being able to see any connection between the atmospheric electricity and the magnetic perturbations. Later I abandoned these observations, because the indications of the electrometers depended too much on local and accidental circumstances." " It should be noted here that the horizontal component of magnetic force varies with the inclination as well as with the intensity of the total force, and the ratio noted above is almost exactly that which would be produced by a change in the inclination alone; and it would appear as if the actual horizontal force, independent of the inclination, was subject to comparatively little variation. This is not improbable, since variations in the horizontal force could correspond only to electro-magnetic easterly or westerly currants, while changes in declination, inclination, and vertical force might correspond to currents from the magnetic north and south, which there is reason to believe are most frequent in auroral displays. To give some idea of the extent of magnetic perturbations, we may mention that during the aurora of 13th May 1869, the declination at Greenwich varied 1° 25', while the vertical force experienced four successive maxima, and the greatest oscillation amounted to 0.01 of its total mean value. The horizontal force at the same time only varied 0.014 of its mean value. During the aurora of the 15th April of the same year the decliration at Stonyhurst varied 2° 23′ 14′′ in nine minutes. The electric currents produced at such times in telegraph wires, though transient, are often very powerful. Loomis (Sill. Jour., vol. xxxii.) mentions cases where wires had been ignited, brilliant flashes produced, and combustible materials kindled by their discharge. It often happens that the ordinary signals are completely interrupted during their continuance. In addition to the resemblance between the auroral phenomena and those of electric discharges in rarefied gases which we have already mentioned, we have seen that auroral displays are accompanied by marked disturbances both in the direction and force of terrestrial magnetism. This fact is in itself almost proof of their electrical character, and, taken in conjunction with the strong "earth-currents" which are at such times produced in lines of telegraph, and with the manifest polarisation of the arches and rays with regard to the magnetic meridian, may be considered as conclusive that the aurora is some sort of electric discharge. There are still some points with regard to the origin of this electricity which are unexplained, and it is uncertain whether the magnetic disturbance causes the electrical phenomena, or vice versa. It has been shown by Prof. Plücker that when an electric discharge takes place through rarefied gas in the field of a magnet, it is concentrated in the magnetic curves, which are the only paths in which it can move without being disturbed by the magnet. This is well shown in De la Rive's well-known experiment, *in which an electro-magnet is enclosed in an electric egg. As soon as the magnet is set in action, the discharge, which had before filled the egg, is concentrated into a defined band of light, which rotates steadily round the magnet,-the direction of its rotation being changed by reversal either of the current or of the polarity of the mag. net. If we suppose that the aurora is an electric discharge passing from one magnetic pole to the other, and following the terrestrial magnetic curves, we shall find that the theory agrees with observed facts even in its lesser details. In these latitudes the magnetic curves are sensibly straight and parallel, and are inclined S. E. at an angle of about 70° from the perpendicular, and, by the well-known laws of perspective, will appear to converge towards this point, as, in fact, the auroral streamers do. The streamers should move from east to west, or from west to east, according as the discharge is from north to south, or vice versa, and, in fact, they are in constant motion. Professor Loomis (Sill. Jour. of Sc., xxxiv. 45) gives a catalogue of forty-six cases of such movement, of which thirtyone were from E. to W. and only fifteen in the opposite direction; and as part of these apparent motions are due to a real motion from N. to S., he concludes that the actual motion of the streamers is from about N.N.E. to S.S.W. This would make the north pole the negative electrode, which is most likely usually the case. Prof. Loomis has shown that during auroral displays electrical currents traverse the earth's surface in the same general direction, though subject to great variation in intensity and even to reversal. Waves of magnetic disturbance are also propagated in the same direction (ibid., xxxii. 318). With regard to the arches it is evident that they are generally circles concentric to the magnetic pole, and it is very probable that they are analogous to the striæ often seen in discharges in rarefied gases. Gassiot, quoted by B. V. Marsh (Sill. Jour., xxxi. 316, and Roy. Soc. Proc., vol. x. Nos. 38 and 39), describes an experiment with his great Grove's battery of 400 cells, in which the exhausted receiver was placed between the poles of the large electromagnet of the Royal Institution :-"On now exciting the magnet with a battery of ten cells, effulgent strata were drawn out from the positive pole, and passed along the under or upper surface of the receiver according to the direction of the current. On making the circuit of the magnet and breaking it immediately, the luminous strata tushed from the positive, and then retreated, cloud following cloud with a deliberate motion, and appearing as if swallowed up by the positive electrode." This, as Mr Marsh remarks, bears a very considerable resemblance to the conduct of the auroral arches, which almost invariably drift slowly southward; and we cannot do better than sum up his theory in his own words :-"The foregoing considerations seem to render it probable that the aurora is essentially an electric discharge between the magnetic poles of the earth leaving the immediate vicinity of the north magnetic pole in the form of clouds of electrified matter, which float southward through the atmosphere at a height of 40 miles or more from the earth, sometimes to a distance of more than 30° from the pole; that whilst they are thus moving forward. with a comparatively slow and steady motion, or sometimes even remaining almost stationary for a long time, bright streams of electricity are from time to time suddenly shot out from them in a nearly vertical direction, that is to say, in the magnetic curves corresponding to the points from which they originate; that these curves, ascending to a great height beyond the atmosphere, then bending more and more southward and downward until they finally reach corresponding points in the southern magnetic hemisphere, are the pathways by which the electric currents pass to their destination; and that for several hundred miles from the earth these curves are thus traced through space and illuminated with bright electric light;' and further, that the magnetism of the earth also causes these luminous currents and the electrified matter composing the arch to revolve round the magnetic pole of the earth, giving them the motion from east to west, or from west to east, which the components of the arch are observed to have." The principal difficulties and deficiencies of this hypothesis, which was first suggested by De la Rive, are that it makes no attempt to account for the origin of such an electrical discharge, and that it is difficult to understand how an electric current can traverse vast spaces of the almost perfect vacuum which must exist at the distance from the earth (many hundreds of miles) which is attained by the magnetic curves, since, in the best vacuums of our Sprengel pumps, discharge will not take place even across the interval of a few centimetres. It is not, however, certain that stellar space is an insulator, and it is possible, moreover, that the auroral currents do not follow the magnetic curves through their whole course, since electric discharge is always in the path of least resistance, and this is modified not only by the magnetic forces, but by atmospheric density, and it is possible that on attaining a certain height the current may proceed horizontally on a stratum of least resistance. It need create no surprise that the discharge is generally invisible in the intermediate zone of low latitudes, since this is well accounted for not only by the large surface over which it is spread at great heights, but because this part of its course is at right angles to the line of sight, while in higher latitudes we look at the streamers almost "end-on," and thus have before our eyes a very great depth of luminous gases. It is common enough, too, in discharges in rarefied gases to see the two poles surrounded by luminous auræ, while the intermediate space is almost or quite dark, or consists of luminous disks or striæ separated by dark spaces. It seems probable that this "glow" discharge in rarefied gases is really a sort of electrical convection, which is propagated comparatively slowly, and from particle to particle; and that the striae are surfaces at which the difference of potential of the moving molecules is so great as to cause discharge between them, while in the intermediate dark spaces the electric force is carried mechanically and silently by the particles moving in regular currents under the repulsive and attractive forces of electrification. On this hypothesis the auroral discharge becomes comprehensible, since we have only to suppose that the electricity is carried mechanically, as it were, through the vacuous spaces, which, if they contain no matter to conduct electricity, can contain none to impede the motion of the molecules. It is, moreover, by no means certain that the bright rays indicate actual currents. They may simply consist of matter rendered luminous in the arches, and projected by magnetic or electrical repulsion in the curves of magnetic force, since Varley (Roy. Soc. Proc., xix. 236) shows that when a glow discharge in a vacuum tube is brought within the field of a powerful magnet, the magnetic curves are illuminated beyond the electrodes between which the discharge is taking place as well as within the path of the current; and also that this illumination is caused by moving particles of matter, since it deflected a balanced plate of talc on which it was caused to impinge. It has also been shown that in electrical discharges in air at ordinary pressures, while the spark itself was unaffected by the magnet, it was surrounded by a luminous cloud or aura, which was drawn into the magnetic curves, and which might also be separated from the spark by blowing upon it. It is evident, therefore, that any mechanical force may separate the luminous particles from the electric discharge which produces them. With regard to the geographical distribution of aurora, Prof. Loomis (Sill. Jour., xxxi.) has laid down a series of zones of equal auroral frequency, and in Petermann's Mittheilungen for October 1874, Prof. Fritz has given a chart embodying the results of his extensive researches on the same subject. He finds, like Prof. Loomis, that the frequency of auroral display does not continue to increase to the pole, but reaches a maximum in a zone which, for the northern hemisphere, passes through the Faroe Islands, reaches its most southern point, about 57°, nearly south of Greenland, passes over Nain on the Labrador coast, then tends northwards, across Hudson's Bay (60° N. lat.), and through great Bear Lake, and leaves the American continent slightly south of Point Barrow. It then skirts the northern coast of Asia, reaching its most northerly point, about 76° N., near Cape Taimyr, passing through the north of Nova Zembla, and skirting the N.W. coast of Norway. Not only are auroral displays less frequent in Iceland and Greenland than further south, but it is found that while south of this zone aurora appear usually to the north of the observer, north of it they are generally to the south, and within it, north or south indifferently. South of this lie other zones approximately parallel to it, and of constantly diminishing frequency. That in which the average yearly number of aurora is 100 passes through the Drontheim, the Orkneys, and the Hebrides, and reaches the American coast just north of Newfoundland. South of this the frequency diminishes rather rapidly. At Edinburgh the annual average is 30, at York 10, in Normandy 5; while at Gibraltar the average is about 1 in ten years. These curves, which Prof. Fritz calls isochasmen, are nearly normal to the magnetic meridians, and bear a close relation to the curves of equal magnetic inclination, especially with those laid down by Hansteen in 1730, while they noticeably diverge in some places from those of Sabine of 1840. They also approximate to the isobaric curves of Schouw, and Prof. Fritz remarks that the curves of greater frequency tend towards the region of lowest atmospheric pressure. It is not unlikely that there may be such a connection, since Prof. Airy has showed a relation between barometric and magnetic disturbances. It will be noticed that, eastward from England, the isochasmic curves tend rapidly northward, Archangel being only on the same auroral parallel as Newcastle. Prof. Fritz points out that they bear some relation to the limit of perpetual ice, tending most southward where, as in North America, the ice limit comes furthest south. He also endeavours to establish some connection between the periods of maximuin of aurora and those of the formation of ice, and considers ice as one of the most important local causes which influence their distribution. He quotes a curious fact mentioned by several Arctic voyagers, that aurora was most frequently seen when open water was in sight, and usually rather in the direction of the water than of the magnetic north. In this connection it may be well to remind our readers that the water of the Arctic regions is always warmer than the ice fields, and must causo upward currents of damp air. For the southern hemisphero there are not yet sufficient observations to make any determination of geographical distribution. With regard to distribution in time Loomis and Fritz and Wolf have shown that there are periodical maxima about every ten or eleven years, and that these maxima coincide both with those of sun spots, and of magnetic disturbance. The following are Fritz and Wolf's dates of maxima : III. زا The annexed chart from Prof. Loomis's paper (Sill. | Jour., April 1873) shows, in a very striking manner, the correspondence of aurora, magnetic variation, and sun A1790 spot area since 1776. It is not improbable that there may also be changes of longer period which our observations are yet insufficient to determine. 1830 Diagram showing Correspondence of Aurora, Magnetic Variation, and Sun Spots. It has frequently been stated that the aurora returned | fluençe might produce the observed magnetic disturbances. periodically on certain days in the same manner as meteors. The arches may be accounted for by the effects of perspecOn the 3d of February brilliant aurora occurred in tive on columns suddenly terminated at a uniform height 1750 and 1869, and on the 4th in 1869, 1870, 1871, by increase of atmospheric density, while the correspond1872, 1873, and 1874; on the 13th February in 1575, ences with iron lines in its spectrum are sufficiently close 1821, 1822, 1865, and 1867; on the 6th March in 1716, to favour the idea. Ferruginous particles have been found 1777, 1843, 1867, and 1868; on the 9th September in in the dust of the Polar regions (E. A. Nordenskiold, Ast. 1776, 1827, 1835, 1866, 1868, 1872, and on the 29th in Nach., 1874, § 154), but whether they are derived from 1828, 1840, 1851, 1852, 1870, and 1872. This conclu- stellar space or from volcanic eruption is uncertain. The sion, however, is not supported by systematic investigation. yearly and eleven-yearly periodicity of aurore tends to A considerable catalogue of aurora was divided into decen- support the theory, but it is a formidable difficulty that, nial periods, and it was found that the maxima of one while shooting stars are more frequent in the morning, or period rarely coincided with those of others, and that the on the face of the earth, which is directed forwards in its larger the number of years taken into account the less orbit, the reverse is the case with aurora. Groneman prominent the maxima appeared,-evident proof that they meets this difficulty by supposing that in the first case the were only accidental. It may be, however, that if only velocity may be too great to allow of arrangement by the prominent aurora had been considered, more periodicity earth's magnetic force, and that, consequently, only diffused might have been found, or that the periodicity is constant light can be produced. He accounts for its unfrequency for very short periods only. in equatorial regions by the weakness of the earth's magnetic ferce, and the fact that, when it does occur, the columns must be parallel to the earth's surface. Without pronouncing in favour of this hypothesis, it must be admitted that it furnishes a plausible explanation of the phenomenon, although we have no evidence that meteoric dust, even if it exists, would produce the observed spectrum, and, as has been already remarked, the iron coincidences are of little weight. Although no daily periodicity can be affirmed, there are two well-marked annual maxima in March and October, of which the latter is the greater, and two minima-the greater in June and the less in January. In this respect the aurora differs from the sporadic meteors, which have a maximum in autumn and a minimum in spring. It also differs from meteors in the hours of its appearance, the former being most frequent before and the latter after midnight. Although the electric hypothesis is the one generally accepted by scientific men, it is only fair to allude to one that has been recently proposed independently by Dr Zehfuss (Physikalische Theorie, Adelman, Frankfort) and by H. J. H. Groneman of Gröningen (Astronomische Nachrichten, No. 2010-2012). According to this view, the light of the aurora is caused by clouds of ferruginous meteoric dust, which is ignited by friction with the atmosphere. Groneman has shown that these might be arranged along the magnetic curves by action of the earth's magnetic force during their descent, and that their in Although we must confess that the causes of the aurora are very imperfectly explained, we may hope that the rapid progress which the last few years have witnessed in bringing terrestrial magnetism under the domain of cosmical laws may soon be extended to the aurora, and that we shall see in it fresh evidence that the same forces which cause hurricanes in the solar atmosphere thrill sympathetically to the furthest planets of our system in waves, not only of light and heat, but of magnetism and electricity. The following is a list of the most important papers, treatises, and works on this subject:-Berlin Mem. 1710, i. 181; Halley, Phil Trans. 1716, 1719, xxix. 406 xxx. 584; Hearne, Phil. Trans., xxx 1107; Langworth, Huxham, Hallet, and Callendrini, Phil. Trans. xxxiv. 132, 150; Mairan, Traité de l'Aurore Boréale, 1733, 1754; Weidler, De Aurora Boreali, 4to; Wargentin, Phil Trans. 1751, p. 126, 1752, p. 169, 1753, p. 85; Bergmann, Schw. Abh., 200, 251; Wiedeburg, Ueber die Nordlichter, 8vo, Jena, 1771; Hüpech, Untersuchung des Nordlichts, 8vo, Cologne, 1778; Van Swinden, Recueil de Mémoires, Hague, 1784; Cavallo, Phil. Trans. 1781, p. 329; Wilke, "Von den Neuesten Erklärungen des Nordlichts, Schwed. isches Mus., 8vo, Wismar, 1783; Hey, Wollaston, Hutchinson, Franklin, Pigott, and Cavendish, Phil. Trans. 1790, pp. 32, 47, 101; Dalton's Meteorological Observations, 1793, pp. 54, 153; Chiminello, "On a Luminous Arch.," Soc. Ital., vii. 153; Loomis, "Electrical and Magnetic Relations," Sill. Jour. 2d ser., xxxii. 324, xxxiv. 34, Sept. 1870; on "Catalogue, Geog. dist., Sna spots," &c., ibid., 3d ser. v. 245, &c.; B. V. Marsh, Electrical Theory," ibid. 3d. ser., xxxi. 311; Oettingen and Vogel on "Spectrum," Pogg. Ann., cxlvi. 284, 569; Galle and Sirks on "Crown," ibid., cxlvi. 133, exlix. AURUNGÁBÁD, or AURANGABAD, a city of India, in the native state of Haidarábád, or the Nizám's dominions, situated in 19° 51' N. lat., and 75° 21′ E. long., 138 miles from Púna, 207 from Bombay via Púna, and 270 from Haidarábád. It was founded about the year 1620, under the name of Gurka, by Malik Ambar, an Abyssinian, who had risen from the condition of a slave to great influence. Subsequently it became the capital of the Moghul conquests in the south of India. Aurungzebe made it the seat of his government during his viceroyalty of the Deccan, and gave it the name of Aurungábád. It thus grew into the principal city of an extensive province of the same name, stretching westward to the sea, and comprehending nearly the whole of the territory now comprised within the northern division of the presidency of Bombay. Aurungábád long continued to be the capital of the succession of potentates bearing the modern title of Nizám, after those chiefs became independent of Dehli. They abandoned it subsequently, and transferred their capital to Haidarábád, when the town at once began to decline. It is now greatly fallen from its ancient grandeur. The city is but halfpeopled, and is half in ruins, presenting everywhere the melancholy appearances of desertion and decay. The population is, however, still considerable, and in the bázár, which is very extensive, various rich commodities, particularly silks and shawls, are exposed for sale. The walls of the town are similar in their construction to those of all the other cities in this quarter of India, being rather low, | Dara, a brave and honourable prince, but disliked by the Mussulmans on account of his liberality of thought, had a natural right to the throne. Accordingly, on the illness of his father, he at once seized the reins of government and established himself at Dehli The second son, Soojah, governor of Bengal, a dissolute and sensual prince, was dissatisfied, and raised an army to dispute the throne with Dara. The keen eye of Aurungzebe saw in this conjuncture of events a favourable opportunity for realising his own ambitious schemes. His religious exercises and temperate habits gave him, in popular estimation, a great superiority over his brothers, but he was too politic to put forward his claims openly. He made overtures to his younger brother Murad, governor of Guzerat, representing that neither of their elder brothers was worthy of the kingdom, that he himself had no temporal ambition, and desired only to place a fit monarch on the throne, and then to devote himself to religious exercises and make the pilgrimage to Mecca. He therefore proposed to unite his forces to those of Murad, who would thus have no difficulty in making himself master of the empire while the two elder brothers were divided by their own strife. Murad was completely deceived by these crafty representations, and at once accepted the offer. Their united armies then moved northward. Meanwhile Shah Jehan had recovered, and though Dara resigned the crown he had seized, the other brothers professed not to believe in their father's recovery, and still pressed on. Soojah was defeated by Dara's son, but the imperial forces under Jesswunt Singh were completely AURUNGZEBE, one of the greatest of the Moghul routed by the united armies of Aurungzebe and Murad. emperors of Hindustan, was the third son of Shah Jehan, Dara in person took the field against his brothers, but was and was born in October 1618. His original name, defeated and compelled to fly. Aurungzebe then, by a Mahomet, was changed by his father, with whom he was clever stroke of policy, seized the person of his father, and a favourite, into Aurungzebe, meaning ornament of the threw him into confinement, in which he was kept for the throne, and at a later time he assumed the additional titles remaining eight years of his life. Murad was soon removed of Mohi-eddin, reviver of religion, and Alam-gir, conqueror by assassination, and the way being thus cleared, Aurungof the world. At a very early age, and throughout his zebe, with affected reluctance, ascended the throne in whole life, he manifested profound religious feeling, perhaps August 1658. He quickly freed himself from all other instilled into him in the course of his education under some competitors for the imperial power. Dara, who again inof the strictest Mahometan doctors. He was employed, vaded Guzerat, was defeated and closely pursued, and was while very young, in some of his father's expeditions into given up by the native chief with whom he had taken refuge. the country beyond the Indus, gave promise of considerable He was brought to Dehli, exhibited to the people, aud military talents, and was appointed to the command of an assassinated. Soojah, who had been a second time defeated army directed against the Usbeks. In this campaign he near Allahabad, was attacked by the imperial forces under was not completely successful, and soon after was trans- Meer Jumla and Mahomet, Aurungzebe's eldest son, who, ferred to the army engaged in the Deccan. Here he however, deserted and joined his uncle. Soojab was gained several victories, and in conjunction with the defeated and fled to Aracan, where he perished; Mahomet famous general, Meer Jumla, who had deserted from was captured, thrown into the fortress of Gwalior, and died the king of Golconda, he seized and plundered the town after seven years' confinement. No similar contest disof Haidarábád, which belonged to that monarch. His turbed Aurungzebe's long reign of forty-six years, which father's express orders prevented Aurungzebe from follow- has been celebrated, though with doubtful justice, as the ing up this success, and, not long after, the sudden and most brilliant.period in the history of Hindustan. The alarming illness of Shah Jehan turned his thoughts in empire certainly was wealthy and of enormous extent, for another direction. Of Shah Jehan's four sons, the eldest, there were successively added to it the rich kingdoms of with round towers. Bajapore and Golconda, and the barren province of Assam, but it was internally decaying, and ready to crumble away before the first vigorous assault. Two causes principally had tended to weaken the Moghul power. The one was the intense bigotry and intolerant policy of Aurungzebe, which had alienated the Hindus and roused the fierce animosity of the haughty Rajputs. The other was the rise and rapid growth of the Mahratta power. Under their able leader, Sevaji, these daring freebooters plundered in every direction, nor could all Aurungzebe's efforts avail to subdue them. At the close of the long contests between them, the Moghul power was weaker, the Mahratta stronger than at first. Still the personal ability and influence of the emperor were sufficient to keep his realms intact during his own life. His last years were embittered by remorse, by gloomy forebodings, and by constant suspicion, for he had always been in the habit of employing a system of espionage, and only then experienced its evil effects. He died, on the 21st February 1707, at Ahmadnagar, while engaged on an extensive but unfortunate expedition against the Mahrattas. AUSCHWITZ, or OSWIECIM, a town in Galicia, Austria, on the right bank of the Sola, a tributary of the Wechsel, 33 miles W.S.W. of Cracow. It has a population of up. wards of 3800, and carries on a trade in salt. Previous to the first partition of Poland in 1773, it was the seat of a dukedom, which had been united by Sigismund Augustus with the duchy of Zator in 1564. AUSCULTATION (auscultare, to listen), a term in medicine, applied to the method employed by physicians for determining, by the sense of hearing, the condition of certain internal organs. The ancient physicians appear to have practised a kind of auscultation, by which they were able to detect the presence of air or fluids in the cavities of the chest and abdomen. Still no general application of this method of investigation was resorted to, or was indeed possible, till the advance of the study of anatomy led to correct ideas regarding the locality, structure, and uses of the various organs of the body, and to the alterations produced in them by disease. In 1761 Auenbrugger of Vienna introduced the art of percussion in reference more especially to diseases of the chest. This consisted in tapping with the fingers the surface of the body, so as to elicit sounds by which the comparative resonance of the subjacent parts or organs might bo estimated. Auenbrugger's method attracted but little attention, till Corvisart, in 1808, demonstrated its great practical importance; and then its employment in the diagnosis of affections of the chest soon became general. Percussion was originally practised in the manner above mentioned (immediate per- | cussion), but subsequently the method of mediate percussion was introduced by Piorry, and is that now largely adopted. It is accomplished by placing upon the spot to be examined some solid substance named a pleximeter (stroke-measurer), upon which the percussion strokes are made either with the fingers or with a small hammer tipped with india-rubber. The pleximeter consists of a thin oval piece of ivory; but one or more fingers of the left hand applied flat upon the part answer equally well, and this is the method which most physicians adopt. Percussion must be regarded as a necessary part of auscultation, particularly in relation to the examination of the chest; for the physician who has made himself acquainted with the normal condition of that part of the body in reference to percussion is thus able to recognise by the ear alterations of resonance produced by disease. But percussion alone, however important in diagnosis, could manifestly convey only limited and imperfect information, for it could never indicate the nature or extent of functional disturbance, or distinguish between different forms of disease, even in those organs which it had proved to be in an abnormal This consisted of a cylindrical piece of wood, about 12 inches long, with a narrow perforation from end to end, the extremity for applying to the chest having a movable piece of conical form fitting into the cylinder, which was withdrawn by the physician while listening to the sounds of respiration, the complete instrument being used for examining the sounds of the voice and those of the heart. This instrument, though rendered portable by being made to screw into two halves, was inconveniently large and heavy, and was subsequently modified by Piorry to the form now generally used of a thin narrow cylinder of about 7 inches long, with an expansion at one end for applying to the chest, and a more or less flattened surface at the other for the ear of the listener. Having ascertained by careful observation the sounds elicited on auscultation of the healthy chest, Laennec studied the modifications of these as produced by disease; and by comparing cases with one another, and especially by investigating the state of the affected parts after death, he was able, in his celebrated Traité de l'Auscultation médiate, to lay the foundation for a rational system of diagnosis of the great classes of pulmonary and heart complaints. It does not, however, appear to be the case, as Laennec supposed, that mediate auscultation by the stethoscope is superior in an acoustic point of view to immediate auscultation by the unaided ear. On the contrary, sounds are heard louder by the latter than by the former method. Nevertheless, the stethoscope possesses special advantages, among the chief of which are that by its use particular areas can be examined and compared with greater accuracy; that it can be applied to all parts of the chest, and that it can be used in all cases where, from the sex or the bodily condition of the patient, the direct application of the ear is inadmissible. On the other hand, immediate auscultation is to be preferred in the examination of young children, who are readily frightened by the sight, and still more by the pressure upon them, of the stethoscope. The whole subject of auscultation has been greatly elaborated since the time of Laennec, and while some of his opinions have been found to require modification, continued investigation only serves more clearly to demonstrate the value of this method of diagnosis, and to elicit fresh and more accurate results from its employment. Although much remains to be done in the way of the correct interpretation of the phenomena observed in auscultation, yet the facts already established are among the most important |