72 ACOUSTICS ACRE drawn out of a disk produces its own charac- teristic nodal lines or figures. (See Chlad- ni's " Acoustics.") Tones may differ not only in the velocity of their succeeding waves, but also in the form of these waves; this deter- mines the character of the tone which the French call timbre. By it we distinguish the sounds of different instruments, the voices of different persons, &c. Comparative physiology has determined which special portions of the interior structure of the ear are intended for the different functions in the act of hearing, by finding some parts more or less developed in proportion as the animal possesses the ca- pacity of distinguishing variations of sound. So the dog, with no musical ear, distinguishes the voice of his master better than those sing- ing birds which can learn a tune and thus have a musical ear. (See EAH.) Recently experi- menters have succeeded in causing sounds to draw waving lines on slips of moving paper, these waves representing not only the pitch or velocity of vibrations, but by their different forms also the nature of the sounds. In our figures are represented a few illustrations of Bound Lines traced on Paper by the Phonautograph. the waved lines produced by this method of registering the nature of diverse vibrations of the same length and pitch. The apparatus with which this is performed is called a phonauto- graph. In regard to the application of acoustics to architecture, and the construction of build- ings intended for music or public speaking, much learning has been erroneously applied. The elliptical and parabolic forms given to walls or ceilings have not answered expectation, for the simple reason that they concentrate the sound at single points at the expense of others. Experience has however taught a few facts, of which the most important is that an echo is the greatest disturbing influence, and that large smooth walls and ceilings at a distance from the speaker make this disturbance a maximum. Speakers, singers, or musical in- struments must therefore be placed as near to such a wall as practicable ; and when a high flat or arched ceiling causes reflection or re- verberation of sound, as is often the case in large churches, a horizontal sounding board of some 20 or more feet in diameter, thus pro- jecting far beyond the pulpit, and placed as low as possible, only a few feet above the speaker's head, has been found the only effec- tive remedy. It is seen in most of the cathe- drals and large churches on the European con- tinent. Among the earlier writers and inves- tigators must be mentioned Euler, Newton, La- place, Chladni, and Savart; and among the later, Helmholtz, Weber, Konig, Hersclifl, Wulner, and Tyndall. See especially Helm- holtz, Die Lehre von den Tonempfindungen (Brunswick, 2d ed., 1866); Tyndall, "Lectures on Sound;" Peirce, "On Sound," prepared from Herschel's writings; and Wulner, JSx- perimentalphysik (Leipsic, 1871, vol. i.). ACQUAVIVA, Clandlo de, a general of the Jes- uits, born in Italy in 1542, died in 1615. He regulated the studies of the order of Jesuits in an ordinance promulgated at Rome in 1586, which became famous under the title of Ratio Studiorum. He prohibited discussions on the subject of tyrannicide, and his opinions are still regarded as authoritative by the order. ACQUAVIVA DELLE FONTI, a town of S. Italy, province of Terra di Bari, 18 m. S. of Bari ; pop. in 1861, 6,517. It is surrounded by walls, and has a handsome parish church. ACQUI (anc. Aquae Statiellce), a town of Italy, capital of a district of the same name, in the Piedmontese province of Alessandria, on the left bank of the Bormida, 18 m. S. of Alessan- dria ; pop. about 9,000. It is much frequented by invalids for its famous hot sulphur springs, which were well known to the ancient Ro- mans. The remains of a Roman aqueduct are among its curiosities. It contains many hand- some buildings, among them a cathedral, con- vents, a college, and a theological seminary. ACRE (Lat. ager, Ger. acker, a cultiva- ted field), a standard measure of land, con- sisting in England and the United States of 4,840 square yards, or 43,560 square feet. In surveying, it is composed of 10 square chains, the measuring chain being 66 feet long. There are 640 acres in an English statute square mile. The Scotch acre is 1*27 of the English, and the Irish 1 '62; the French and Belgian hectare, 2-47, and the arpent 0-99 (Geneva, 1-27); the Swiss faux, 1'62; the Spanish fanegada, 1'06; the Portuguese gueira, 1'43; the Aus- trian joch, 1-42; the Danish toende, 5'50; the Swedish tunneland, 1'13; the Russian desia- tina, 2'70. The morgen of Germany is gen- erally about 0'65 of an acre, but it has hereto- fore varied in the different states from - 63 to 2-40; in Holland it is 2-10, and in Poland 1-38. The moggia of Naples is 0'83 of an acre ; the giornate of Sardinia, 0*93 ; the saccata of Tus- cany, 1'22. The ancient Roman jugerum was 0'66 of an acre, and the Greek plethron 0'23. ACRE, or St. Jean d'Aere (called Acca by the Turks, Accho in Scripture, and Ace and Ptole- mais by the Greeks), a seaport town of Syria,
