originating in vibrations, or a succession of concussions, must be communicated from the body, in which they are excited, to the sheet of air, or whatever else be in contact with it, and from this again to another sheet beyond the first; thus diffusing the motion in every direction. The agitation of the sounding body must thus be communicated to the surrounding medium to a great distance, and impressed upon any body situated within this distance; if this body be the ear, the tremor excited in it by these agitations will be perceived by the mind. The necessity of some medium for the transmission of sound is proved by experiment. If a bell be rung in an exhausted receiver, the sound will be hardly perceptible, while the tones will become clear and distinct, on re-admitting the air. Having thus given a general outline of the source and propagation of sound, we shall proceed to consider, with as much minuteness as the limits of this work will permit, some of the more important facts connected with them.-The most obvious characteristics, by which we distinguish. different sounds, consist of differences in their degrees of what we call loudness, and acuteness, or pitch. We can produce, at pleasure, sounds having different degrees of loudness, from the same sonorous body, by making the concussions upon it more or less violent; disturbing in a greater or less degree the arrangement of its parts. So two bodies of like substance and figure, but unlike mass, when subjected to the same shock, emit sounds unlike in loudness; and, again, bodies of like mass and figure, but unlike substance, form sounds more or less loud, when subjected to the same shock. In this latter case, the loudness has a relation to the quantity of elasticity possessed by the bodies; and in all cases, when the disturbance of the parts is carried beyond the elastic power of the body, so as to produce a permanent change of figure, no increase of loudness is induced. From a consideration of the preceding facts, we may conclude, that loudness depends upon the quantity of motion, or sonorous vibration, in which it originates. The other principal characteristic of sound, its acuteness or pitch, depends upon the frequency with which the concussions or vibrations of the sonorous body succeed each other. That sounds may be audible to a common ear, it is necessary that the concussions upon the medium, which communicates them, should follow each other in such succes

sion, that not more than 8192, nor less than 32, distinct concussions shall be made upon the medium during the lapse of one second. Some ears, however, can perceive sounds emanating from vibrations a little beyond the extremes to which the perceptions of other ears are confined. We should be careful not to confound the frequency of vibrations with the velocity of vibratory motion. A string may vibrate with a greater or less velocity, as it passes its axis to a greater or less distance; yet the times of its vibrations may be all equal. The difference of velocity, affecting the quantity of motion only, would produce no change, except in the loudness of the sound. To those sounds which proceed from infrequent vibrations, we give the name of grave or low; those from frequent vibrations we call sharp or acute. When vibrations succeed each other in equal times, their sound excites a pleasant sensation, and they are called musical. When two bodies are made to sound together, if their vibrations are performed in equal times, the sounds are said to be in unison. When the vibrations are performed in unequal times, so that some of those of the one are not accompanied by those of the other, the ear perceives a degree of dissonance in the sounds. If, however, the vibrations meet after short and regular intervals, the dissonance is not easily detected, and the sounds are said to accord. During the continuance of most primary sounds, however excited, we perceive other and more acute sounds co-existing with them. These are called their harmonics. They are supposed to originate in a series of secondary vibrations, more short and frequent than the principal vibration. Thus a sounding string, for example, may be supposed not to pass its axis in a simple curve, but to resolve itself into a tortuous line, formed by a number of smaller curves, each of which vibrates across its own axis, thus producing its harmonics. It is perhaps some combination of the harmonics with the primary sound, that characterizes the sound of different instruments, though of the same loudness and pitch, so that we can distinguish one from another. The air, being the common medium which surrounds the ear, is that by which sounds are usually transmitted. This transmission is performed with a velocity of about 1130 feet in a second. All other bodies, however, are capable of transmitting sound. It may be done perfectly, even by the solid parts of the head. If, for example, we hold the stem

of a watch between the teeth, and cover the ears with the hands, the beats are heard more distinctly than when the instrument is held at an equal distance in the air. The rubbing together of two stones under water may be heard, by an ear in the same medium, at the distance of half a mile. When the air, or any other body of indefinite extent, is disturbed, in a point situated within it, by a sonorous vibration, it forms a wave which passes from the disturbed point, as a centre, in every direction. It follows that as the wave extends itself, the mass to be put in motion increases until the original motion is rendered insensible from the magnitude of the mass to which it has communicated itself. The velocity with which waves, thus formed, move through any homogeneous elastic medium, is always equal to that which a heavy body would acquire by falling through half the height of the modulus of elasticity. In applying this law to the transmission of sound by the air, it was for a long time found not to give the same results as were obtained by experiment. The discrepancy, however, has been most ingeniously reconciled by a small correction for the latent heat made sensible by the compression; the effect of this being to increase the height of the modulus of elasticity. We ought, therefore, to find that liquids, and more especially some of the solids, should transmit sound much more rapidly than air; and this agrees most perfectly with various experiments. Cast-iron, for example, has been found to transmit sound with a velocity 10 times greater than air. Sound does not readily pass from one medium to another; a sound made in the air is not easily distinguished under water, although the distance be very small. It is from this, probably, that cork and all soft cellular bodies are bad conductors of sound, as in these the sound must, in passing through the walls of the cells and the air contained in them, change successively from one medium to another. All sounds, whatever be their loudness or pitch, are transmitted with the same velocity; a fact most completely proved by every musical performance. Were it otherwise, indeed, this beautiful art could not exist. To make this apparent, it is only necessary to consider, that harmony is a combination of different sounds arranged with certain relations of time and pitch. Now, if one sound were transmitted with *The height of the modulus of elasticity of air is

27,800 feet.

VOL. I.

4

greater velocity than another, these relations would differ at different distances, or be confounded, except at a single given point. Nay, further; melody, which is a succession of single sounds, would not reach different ears with the same relations of time, if the different notes were not transmitted with equal velocities. Some observations on sound, in very high latitudes, seem to contradict the above law of transmission. The seeming anomaly, however, is sufficiently reconciled by supposing the different strata of air, through which the sounds, in those instances, were transmitted, in very dif ferent hygrometrical or thermometrical states; which would make corresponding differences in their modulus of elasticity. When a wave of sound meets an elastic surface, it is partly transmitted and partly reflected. This reflection, when it returns back perpendicularly, is called an echo. That an echo may be distinctly heard, it is necessary that the reflecting surface be at such a distance that the original sound shall have ceased before the reflected one returns to the ear; otherwise they will be blended, and the echo not perceived.-Hitherto we have considered the propagation of sounds in an unconfined medium, particularly the air, in which the wave of sound can diffuse itself in every direction. When this diffision is prevented by enclosing the medium in a surface capable of reflecting the wave so that the sound shall be confined to one direction, the transmission from one point to another is much more perfect. Experiments have been made in this way, in which a hollow cylinder, about half a mile long, was formed by castiron pipes. The sound was transmitted by the air, in this cylinder, with wonderful distinctness. The least whisper, at one end of the cylinder, was distinctly heard at the other end. So perfect, indeed, was the transmission, "that, not to hear, it was absolutely necessary not to speak." Captain Parry and lieutenant Foster made several experiments, during the northern expeditions, to ascertain the velocity of sound. A table of them is given in a number of the Edinburgh Philosophical Journal. These experiments were made at Port Bowen, by means of a brass six-pounder, over a range of 12,892.89 feet. The results given are the mean of four shots in one case, of five in another, and, in the rest, of six shots by each observer. The mean results varied from 12",7617 to 11",7387 and 11",5311 for the time in which the range of 12,892.89

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feet was traversed by the sound. At the period of the experiment which gave the first of these results, there was a calm; during the second, the wind was light; during the third, a strong wind was blowing. The velocity per second, in feet, was, in the first instance, 1010.28; in the second, 1098.32; in the third, 1118.10. Omitting the last of the ten results (the last above given), on account of the strong wind, the mean of the other nine gives a velocity of 1035.19 feet, at the temperature of 17.72, Fahrenheit.-The mean of a table of velocities formed from observations made at Fort Franklin, by lieutenant Kendall, who accompanied captain Franklin, in his second journey to the shore of the Polar sea, gives a velocity of 1069.28 feet per second, at the temperature of 9.14, Fahrenheit.-The science of acoustics, like the other physical sciences, has been in a constant state of advancement since the revival of learning. It appears that Pythagoras knew the relation between the length of strings and the musical sounds which they produce. Aristotle was not only aware of this relation, but, likewise, that the same relation subsists between the length of pipes and their notes, and that sound was transmitted by the atmosphere. This constituted the sum of ancient learning in this branch of science. These facts were taught by Galileo, and, moreover, that the difference in the acuteness of sounds depends on the different frequency of vibrations, and that the same string, if of uniform thickness and density, must perform its vibrations in equal times. But, without attempting a history of modern discoveries in acoustics, we can only mention, that the names of Taylor, Moreland, Newton, Daniel Bernouilli, D'Alembert, Euler, Robison, Lagrange, Laplace, Chladni, T. Young and Biot are all connected with it. Of these, Newton gave the law of transmission, which we have stated in this article, and the correction for heat was made by Laplace.

ACRE; a measure of land, containing four square roods, or 160 square poles or perches. The statute length of a pole or perch is 5 yards, or 16 feet; but the length of a pole, and, therefore, the size of the acre, varies in different counties in England. The Scottish acre contains also four square roods; one square rood is 40 square falls. The English statute acre is about three roods and six falls, standard measure of Scotland; or the English acre is to the Scottish as 78,694 to 100,000. The French acre, arpent, is

equal to 54,450 square English feet, of which the English contains only 43,560. The Welsh acre contains commonly two English ones. The Irish A. exceeds the English by two roods, 1927 perches, The U. S. of A. use the English statute A. ACRE (Akka, St. Jean d'Acre); in the middle ages, Ptolemais, a city and harbor on the coast of Syria, capital of a Turkish pachalic, between the pachalics of Damascus and Tripoli, which contains 420,000 inhabitants, and 6275 sq. miles. This city, situated at the foot of mount Carmel, is the chief emporium of Syrian cotton, and contains about 16,000 inhabitants; its harbor, though full of sandbanks, is still one of the best on this coast. At the time of the crusades, A. was the principal landing place of the crusaders, and the seat of the order of the knights of St. John as late as 1291; hence the French name, St. Jean d'Acre. The Turks, under Djezzar, pacha of this place, who is famous for his cruelty, sustained, with the assistance of the British commodore Sidney Smith, a siege of 61 days, by the French army under Buonaparte. After a great loss of men on all sides, the French abandoned the siege. (See Egypt, landing of the French in.)

ACRIDOPHAGI (Gr., from àzois, a locust, and yw, to eat); an ancient Ethiopian people, who are said to have fed on locusts.

ACRISIUS; the father of Danaë. (See Danaë.)

ACROCERAUNIUM; in anc. geogr. a promontory of Epirus, on which are situated the Acroceraunia or montes Ceraunii. They run between the Ionian sea and the Adriatic, where Illyria ends and Epirus begins, and are the modern Monti della Chimera.

ACROCORINTHUS; a steep rock, about 2100 feet high, near the city of Corinth, of a gray color, and picturesque form, crowned with the remains of old Venetian fortifications, repaired a little by the Greeks, since the commencement of their revolution. It was famous, in ancient times, for its citadel, and on its top stood, according to Pausanias, a temple of Venus. At its foot is a fountain, the ancient Pyrene. The shape of the A. is that of a truncated cone. This little fortress has been several times taken and retaken in the war between the Greeks and Turks. The view from the top is one of the most charming in the world. It is thus described in the "Journal of Dr. Lieber," before whom no Christian traveller, in modern times, had probably visited it, as the

Turks did not allow Christians to ascend it while it was in their hands:-"The view from this spot amply rewarded me for my trouble. To the north lay the high and snowy summits of Helicon and Parnassus, as described by Strabo, extending far under the clear blue of a southern sky. On the west was seen the bay of Crissa, mount Citharon, and the promontory of Olmiæ. On the east the Saronic gulf washes the islands of Salamis and Ægina. To the north-east lay the shore of Attica. There we could see Pentelicus, Hymettus and Laurion, and even down to the cape of Sunium. The day was very clear, so that I could discern the acropolis of Athens. To the south I could see far into the territory of Argolis. To the west Achaia and Sicyonia lay in sight. The view comprehended the scenes of the best displays of Grecian art, science and valor."

ACROPOLIS (Greek); the highest part or citadel of a city, particularly that of Athens, where the treasury and public records were kept. It is situated on a rock, and has often been the subject of contest in the late war between the Greeks and the Turks.

ACROSTIC (Greek); a poem, of which the first, and sometimes the final letters of the lines or verses form some particular word or words. The middle letters, also, are sometimes used for the same purpose. An example of the three kinds united may be seen in the following Latin hexameters: Inter cuncta micans I gniti sidera cœl I, Expellit tenebras E toto Phoebus ut orb E; Sic cæcas removet IESUS caliginis umbra S, Vivificansque simul V ero præcordia mot U, Solem justitiæ S ese probat esse beati S. The French abbés and nobles, before the revolution, often exercised their ingenuity in the composition of these poetical trifles. The French Encyclopédie moderne says, L'acrostiche était alors un poëme de cour ou de ruelle.

ACT, in law; an instrument in writing for declaring or justifying the truth of any thing. In this sense, records, decrees, sentences, reports, certificates, &c. are called acts. The French lawyers distinguish between, 1, private records (actes sous ceing privé), which must be acknowledged by the parties, in order to have legal force; 2, public documents (actes authentiques), which have legal force, without being acknowledged by the parties, as long as they are not proved spurious; and, 3, executive acts (actes exécutoires), which, until their genuineness is called in question (inscription à faux), are also binding

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without acknowledgment by the parties subject to their operation. Of this kind are the records of the public notaries (actes notariés), and all the official documents of the French courts of justice. In England and the United States, act implies decree; hence, an act of parliament is a decree of parliament, confirmed by the king, a statute. (See Great Britain.) At the close of each annual session, the decrees or acts of parliament are collected into one body, which forms the statute of that session, the several decrees of which are contained in separate chapters. They are quoted according to the year of the king's reign, and according to the chapter; e. g. the act of habeas corpus is the second chapter of the statute of the year 1680, the 31st year of the reign of Charles II, and is quoted, 31 Ch. II, c. 2. In America, there is no uniform mode of quoting statutes: each separate act is deemed a distinct statute. Generally, the acts are cited by their date and year; and, if more particularity is necessary, by the chapter, when the statutes are divided into chapters. Acts in Germany are the records and documents of any transaction, especially of a lawsuit. The whole process, in that country, is carried on in writing. Nothing is received as evidence, unless laid before the court on paper. When a criminal process begins, the prisoner is brought before a judge or assistant and a writer. The judge questions: the question is written on the left side of a folio sheet; on the right side the answer of the prisoner is set down. The same takes place with every witness. The reader can imagine to what an immense bulk these acts often increase in the course of a single process. If there are witnesses in other places, an order to examine them is sent, and the papers containing the minutes of their testimony are transmitted to the place of trial. The examining judge is called the judge of inquisition (inquisitions-richter). At the close of each stage of the exami nation, the prisoner subscribes the minutes made during that time with the words, "read in my hearing, approved and signed." He also signs his name, as do likewise the judge and the writer. When the acts are completed (closed), they are delivered to the court, who appoint another judge to report on them and move for judgment, while another still acts as counsel for the prisoner. Afterwards, the whole court in pleno decides. In fact, in Germany, the whole course of administration is conducted in writing. In Saxony, such acts are almost

endless. In Prussia, also, they are very numerous. All acts are preserved in archives. After sentence passed in one court, the whole pile of acts is sent to a court of appeal.

ACT, in the universities, signifies a thesis maintained in public by a candidate for a degree.

ACT OF FAITH. (See Inquisition.) ACTA ERUDITORUM; the first literary journal that appeared in Germany. It enjoyed a long existence and great popularity. The example set by the Journal des Savans, and by the Giornale de' Litterati, but especially the increasing spirit of enterprise and activity among the German booksellers, induced Otto Mencke, professor at Leipsic, to lay the foundation of this periodical publication, in 1680. Having formed the necessary connexions, on his travels through Holland and England, and being assisted by the most eminent German scholars, he commenced the journal in 1682, which increased in popularity from year to year. Among the contributors were Carpzov, Leibnitz, Thomasius, &c. Its object was, to give a faithful and particular account of books; and it was conducted on the same plan, even after a better taste in composition and greater independence were introduced into literary discussions in the French journals published in Holland. The German journal began, however, to decline gradually in value, and in the number of its subscribers, particularly after 1754; and the irregularity of its appearance became at length so great, that the last volume, for 1776, was published in 1782, exactly a century from the time when the journal was commenced. The whole consists of 117 volumes in 4to., including the supplementary volumes and indices. Leibnitz, in this journal, first gave to the world his notions respecting the differential calculus.

ACTA SANCTORUM; a name sometimes applied to all collections of accounts of ancient martyrs and saints, both of the Greek and Roman churches. It is used more particularly as the title of a voluminous work, comprising all those accounts, which was commenced at the instigation of the Jesuits, in 1643, by John Bolland, a Jesuit of Antwerp, and after his death continued by other divines of the same order, known by the name of Bollandists, (q. v.) to the year 1794, but not yet finished, (Antwerp, Brussels and Tongerloo, 1643-1794, 53 volumes in folio.) Some imperfect notices of persons distinguished for their holy lives and religious constan

cy, during the period of the persecution of Christian believers, are found as early as the second and third centuries; particular narratives and biographies commenced with the 4th century, and were infinitely multiplied till the close of the middle ages. Since the 6th century, many works have been compiled from this immense mass of materials. The first critical collection of original legends was edited by Boninus Mombritius, in 1474. The above-mentioned collection, however, surpasses all others of the kind in extent, fidelity and impartiality. It is likewise distinguished for sound criticism and excellent illustrations, which will make it forever a most valuable storehouse of ecclesiastical history, if truth is critically separated from fiction and superstition, by the historian who describes the manners and the spirit of those ages.

ACTEON; in fabulous history, the son of Aristæus and Autonoë; a great hunter. He was turned into a stag, by Diana, for looking on her when she was bathing, and was torn to pieces by his own dogs. Also, a Corinthian youth, killed by Archias, one of the Heraclidæ, in an attempt to carry him off from his father's house.

ACTION (law) a term including private suits and public prosecutions. Actions are, therefore, criminal or civil; criminal, for the punishment of crime; civil, for the obtainment of right. Civil actions are divided into real, personal and mixed. Action real is that whereby a man claims title to lands or tenements in fee or for life. Action personal is brought upon contracts, or injury to person or estate. Action mixed lies for a thing and against the person who has it. It seeks an object, and a penalty for its detention. Many personal actions die with the person. Real actions survive. In all actions merely personal, for wrongs actually committed by the defendant, as trespass, battery, slander, the action dies with the person, and never can be revived, either by or against the executors or other representatives. But in actions on contracts, where the right descends to the representatives of the plaintiff, and those of the defendant have received effects from the deceased sufficient to answer the demand, though the suits abate by the death of the parties, yet they may be revived against or by the executors. Again, actions are either local or transitory. Actions, real or mixed, for the recovery of the freehold, or for damage done to it, are to be brought in the same county where the land lies. Actions on