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 AOONITIA ACOUSTICS 69 ACONITIA. See ACONITE. ACOSTA. I. Jos6 de, a Spanish writer, born about 1539, died Feb. 15, 1600. He entered the society of Jesuits at 14, and on completing his course of study was appointed professor of theology at Ocafia. In 1571 he was sent as a missionary to South America, of which, after his return to Spain, he published a history (Historia natural y moral de las Indias, Madrid, 1590). This work has been translated into several languages. He also wrote De Natura Novi Orbis, and some other works, chiefly of a polemical character. II. Uriel, a Jewish writer, born in Oporto, Portugal, about 1590, died by his own hand in Holland in April, 1647, or, according to some accounts, in 1640. He belonged to a family converted to Christianity at the time of the expulsion of the Jews from Portugal, and was educated by Catholic teachers, but soon con- ceived doubts concerning the Christian doc- trines. He finally fled, with his mother and a brother, to Amsterdam, embraced the faith of his ancestors, and exchanged his original name Gabriel for Uriel. He failed, however, to recognize in the rabbinical Judaism of his time the ideal of his independent specula- tions, and became involved in a passionate controversy with the religious heads of the Jewish congregation of Amsterdam, in the course of which, having suffered excommu- nication, he published in Portuguese a " Criti- cism of the Pharisaic Traditions, compared with the Written Law," in which he repu- diated the doctrine of the immortality of the soul. He was now arraigned before the magistrates and heavily fined. After many years of exclusion from the synagogue he signed a recantation of his views, but sub- sequently again provoked the ire of the orthodox, among whom were his own rela- tives, was a second time excommunicated, and finally submitted to an ignominious public chastisement. Maddened by persecution, he put an end to his life by a pistol shot, leaving an autobiography, which was published in Latin and German in 1687. III. Joaqnin, a South American historian, colonel of engineers in the Colombian service, died about 1862. In 1834 he explored the valleys of the So- corro and Magdalena rivers with the bota- nist Cespedes, and in 1841 made researches relative to the Chibchas and other aboriginal tribes. He continued these investigations in the archives of Spain and France, and in 1848 published in Paris Compendia historico del descubrimiento y colonization de la Nueva Granada, en el siglo decimo sexto. In 1849, in conjunction with M. A. Laserre, he pub- lished a new and enlarged edition of the celebrated Semenario de la Nueva Granada, with a biographical notice of the author, the learned Caldas, who was shot in 1816. A series of archaeological essays were furnished by Acosta, for publication, to the Paris geographical society, 1854 et seq. ACOUSTICS (Gr. aitoiieiv, to hear), that branch of physical science which explains the phe- nomena and laws of sound. For the produc- tion of these phenomena three conditions are required: 1, a sonorous body; 2, a medium to propagate, and 3, an organism to perceive the sound. From these conditions the science of acoustics is naturally divided into three branches, of which the last belongs entirely to the field of physiology, or rather biology, while in the first two the most intricate and at the same time most successful application of mathematics to mechanical science is to be found. A superficial examination into the cause of sound shows that it originates in vibrations of the sounding body, and is thus a result of its elasticity. The air, being very elastic, is ordinarily the medium by which sound is transmitted to our ears; but most other bodies, solid as well as liquid, transmit sound as well and even better than air, while in a vacuum transmission ceases, as is proved by the well-known experiment of exhausting by means of an air pump the air from around a continuously ringing bell. The phases of the sonorous vibrations are appropriately called un- dulations or waves ; they are communicated to the body transmitting the sound by one or more impulses from the sonorous body, and are transmitted by alternate compressions and expansions of the parts. The velocity of this transmission for air at the freezing point of Fahrenheit is 1,090 feet per second, and about one foot more for every degree above. Very violent sounds, however, travel faster, as proved by Boyden in Boston and Earnshaw in Shef- field, England; the cause of this is the heat developed by strong compression of the air by a powerful wave of sound. Heavy gases transmit sound slower and light gases faster than air: carbonic acid 858 feet, hydrogen 4,164 feet per second. Water transmits sound with about the same velocity as the latter, while alcohol, ether, and turpentine transmit it slower (3,800 feet), and saline solutions hi water faster (from 5,000 to 6,500 feet per sec- ond). Through metals the transmission is in round numbers as follows: lead, 4,000 feet per second; copper, 11,000; iron and steel, 16,000. If a wave is violent enough to pro- duce a shock against the drum of the ear, a sound is always heard even if there be but a single wave ; such is the case with a clap of thunder, the explosion of a gun, or the crack of a whip. But if the waves are weak, such as those produced by the vibration of a string, there must be a succession of them at a cer- tain rate of rapidity, in order to make the sound audible. If these waves succeed one another at regular intervals and thus have equal lengths, we have a musical tone ; if irregular, they produce merely a noise. The lowest tone used in music is produced by an organ pipe nearly 32 feet long, in which the tone is pro- duced on the same principle as in the flute, by blowing a current of air against a sharp edge ;