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to the development of the religious ideas resting on rational arguments only, and positive or revealed theology, which sets forth and systematizes the doctrines of the Scriptures and of the church. Revealed theology or Biblical theology is occupied solely with the investigation and representation of the doctrines contained in the Bible. A distinction is made between theoretical theology or dogmatics and practical theology or ethics. Theology, viewed as the whole of religious science, is commonly regarded as consisting of four main branches, historical, exegetical, systematic, and practical or moral theology. These are again variously subdivided, and several auxiliary sciences are connected with them. Thus historical theology embraces the history of the church, of Christian doctrines, of heresies, of councils, &c. To exegetical theology belong the interpretation (exegesis) of the Bible; hermeneutics, the science which teaches the right principles to be observed in interpreting the Bible; criticism, which investigates and tries to establish the genuine original text; the introduction to the Bible, which discusses the time when and place where each book of the Bible originated, its authenticity, and kindred questions. Systematic theology, also called merely theology, comprises the system of Christian doctrines (dogmatics); the system of Christian ethics; symbolics, the comparative statement of the doctrines of the several religious denominations, &c. Practical theology includes homiletics, catechetics, liturgics, ecclesiastical law, &c. Polemics and apologetics, which are also often treated as separate branches of theology, belong to several of the above four principal divisions at the same time.-Until the time of Abélard little attention was paid to comprehending | theology in its totality, and to establishing the connection of the branches with each other. Although nearly all the theologians of the middle ages whose writings are extant belonged to the same church, yet they were divided into two fundamentally different schools, the scholastics and mystics. The theologians of the churches which grew out of the reformation of the 16th century followed, in their treatment of theology, either the scholastics or mystics, though the name of the former was discarded both by their Protestant and Roman Catholic followers. A new era in the history of theology was inaugurated by the philosophy of Kant, who fully developed and systematized a new theory of Christian theology, commonly called rationalism, which more or less made the belief in a religious doctrine dependent on its demonstrability by reason. This view gained the ascendancy in several Protestant churches. Its opponents, who defended the Bible as the absolute rule of faith, were called supranaturalists, and the subsequent history of theology is a contest not yet ended between these two systems. The chief arena of this controversy has been Germany; but it has had little or no influence over Roman Catholic schools. It has

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also been attempted to build up theological systems in opposition to Christianity, such as deism and pantheism.-In Roman Catholic schools, theology is divided into dogmatic and moral. Dogmatic theology, considered in its various methods of exposition and demonstration, is termed positive theology when it bases its proofs on Scripture and tradition. Meral theology treats of divine and human law as the rule of our actions. It aims at determining the true sense of the decalogue and the gospel precepts, discusses virtues and vices, examines the principles of justice and the foundations of injustice, points out what is needful and unlawful, and teaches all Christians their respective obligations in all states, conditions, and offices. Moral theologians are often called casuists, from their treating ex professo of “cases of conscience." Scholastic theology is that peculiar method introduced into the schools during the 11th and 12th centuries. It reduced all doctrinal matters into one body, so coordinating them that one question explained and completed another, binding them into a connected and systematic whole; it observed in its every demonstration the strict process of syllogistic reasoning, making use of the admitted principles of metaphysics, and thus conciliating faith with reason, and religion with philosophy.-Valuable systematic works, giving a survey of the entire field of Christian theology, have been published by President Dwight, Dr. J. Pye Smith, Prof. Hodge ("Systematic Theology," 3 vols. 8vo, New York, 1872-3), and others, and useful encyclopædic manuals by Hagenbach, Pelt, and Staudenmaier.

THEOPHRASTUS, a Greek philosopher, born at Eresus, in the island of Lesbos, about 372 B. C., died about 287. His original name was Tyrtamus, and he was surnamed Theophrastus probably for his eloquence. He studied at Athens under Plato and Aristotle, and succeeded the latter at the lyceum. The number of his pupils from all parts of Greece was at one time 2,000. His influence on public affairs excited a party spirit against him, and being brought before the Areopagus on a charge of impiety, he pleaded his own cause, and was acquitted. After this he taught in tranquillity till 305, when Sophocles, son of Amphiclides, carried a law which prohibited all philosophers, under pain of death, from giving any public instruction without the permission of the state. Theophrastus left Athens; but in the next year the law was abolished, and he returned. He wrote works on politics, laws, legislators, and oratory, which are lost, and "A Dissertation on the Senses and the Imagination," a work on "Metaphysics," "Characters," and two works on botany, The History of Plants" and "The Causes of Plants," which are extant in whole or in part. The book of "Characters" consists of 30 sketches of the general vices of humanity as developed in individuals. His extant works were first printed with those of Aristotle (Venice, 1495-'8); the best edition

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is Wimmer's (Leipsic, 1854, and Paris, 1866). His "Characters" were translated into French and prefixed to his own by La Bruyère (1688), and into English, among others, by Francis Howell (London, 1824).

THEOPHYLACT (Oeopuháктos), surnamed SIMOCATTA, a Byzantine historian, born of an Egyptian family in Locris in the latter part of the 6th century, died about 629. From 610 till about the close of his life he held various offices at Constantinople. He wrote a history of the reign of the emperor Maurice (582-602), of which a Latin translation, Historia Mauricii Tiberii Imperatoris Libri VIII., was published at Ingolstadt in 1648. Besides 85 letters (Epistola Morales, Rustica et Amatoria, 4to, Cracow, 1509), he wrote a work on the nature of animals, especially of man ('Aropíaι Ovσikai, or Quæstiones Physica, 4to, Leyden, 1596; Leipsic, 1653.) These two works were published together at Paris in 1835.

THEOPHYLACT, a Greek theologian, born in Constantinople probably about the middle of the 11th century, died after 1112. He was instructed by Clement, archbishop of Bulgaria, and became archbishop of Achris or Achrida, a chief city of Bulgaria, between the years 1070 and 1077. He engaged in the controversies of his day, especially those relating to the true character, procedure, and office work of the Holy Ghost, and the question whether or not common bread or only unleavened should be used in the sacrament, opposing the views of the Latin church. He compiled commentaries upon the minor prophets and a large part of the New Testament from the works of Chrysostom, and wrote a treatise on royal education (IIaudeía Baoiλikh, or Institutio Regia) for the instruction of his pupil Prince Constantine Porphyrogenitus, the son of Michael VII. There exist 75 of his letters, with some homilies and orations and a few small treatises. An edition of all his works in Greek and Latin was issued at Venice (4 vols. fol., 1754-'63).

THERA (now Santorin), an island of the Egean sea, now forming with Amorgos and other islands an eparchy of Greece, in the nomarchy of the Cyclades; length about 9 m. from N. to S., average breadth about 4 m.; pop. about 13,000; of the eparchy, in 1870, 21,907. It was originally circular, but the islet Therasia was torn from it by an earthquake about 237 B. C., and it now resembles a horseshoe. The harbor thus formed is the crater of a volcano, and as no bottom is found, vessels make fast to the abrupt and rocky shores. The soil is volcanic and inclined to dryness, but very fertile. The annual production of wine is about 1,750,000 gallons. Ship building is the only considerable industry. Thera, the capital, had a population in 1870 of 5,143.Though an ancient Lacedæmonian colony, Thera is only of historic importance as having sent a colony to found the city of Cyrene in Africa, 631 B. C. The dates of the eruptions

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known to have taken place in or near this island are 197 B. C. and A. D. 46, 726, 1573, 1707, and 1866. By that of 197 B. C. the island of Palæa (Old) Cammeni was formed, by that of 46 Mikra (Little) Cammeni, and by that of A. D. 1707 Nea (New) Cammeni. The last was at first composed of white pumice, but subsequently received additions of brown trachytic rock. The eruption did not wholly cease or the island assume its present form till 1712. In the beginning of 1866 stones flew up from the port of Volcano, and a new volcano arose which attained a height of about 100 ft. The eruptions continued until the autumn of 1870, and enormous quantities of lava were thrown out, surpassing in size those projected in 1707– '12. Near Nea Cammeni a regular cone was formed 325 ft. high.

THERAMENES, a political leader at Athens toward the end of the 5th century B. C., born in Cos. In 411 he became a member of the council of 400; but he deserted it and became one of the leading agents in its overthrow. In 410 he joined the fleet under Thrasy bulus, and took part in the battle of Cyzicus; and in 408 he participated in the siege of Chalcedon and the capture of Byzantium, under Alcibiades. He was one of the inferior generals at the battle of Arginusæ in 406; and it was chiefly through his influence that six of the commanders were condemned to death for not saving the drowning crews, although, as they asserted, he had himself been sent with others to perform that office. During the siege of Athens by the Spartan general Lysander, when the city was reduced to great extremity, Theramenes was sent as envoy to the Lacedæmonians. He remained three months with Lysander, who he pretended detained him that length of time without informing him that the ephors only had power to grant peace; and upon his return to the city, which was now suffering under a terrible famine, he was sent back to make peace on any terms. The hard conditions imposed by the Lacedæmonians were assented to (see GREECE, vol. viii., p. 195), and in 404 Theramenes, who during his three months' stay with Lysander had made arrangements with the Athenian oligarchical exiles, was among the most active in subverting the constitution, and became one of the thirty tyrants. He warmly supported the first measures of the government in crushing the democracy and putting to death its prominent leaders; but he afterward opposed the violent measures of Critias and his colleagues. His party daily increased; but Critias, after charging him with being a public enemy, caused him to be dragged off to prison by partisans with concealed daggers whom he had brought into the senate house, and compelled him to drink the hemlock.

THERESA, or Teresa, Saint, a Spanish mystical writer, born in Ávila, March 28, 1515, died at Alba, Oct. 4, 1582. She was called Teresa de Ahumada (her mother's family name) till Au

gust, 1562, when she assumed that of Teresa | de Jesus. At the age of 20 she entered the order of Carmelites in a convent of her native town, in which she remained 27 years. She then founded a reformed branch of the Carmelites (Barefooted Carmelites), sometimes called after her Theresians. During her life 29 convents of the reformed order were established, and in the 18th century it counted about 2,000 members in six provinces, in Spain and Spanish America. She was beatified by Pope Paul V., April 24, 1614, and canonized by Gregory XV., March 22, 1622, her feast being fixed on Oct. 15. Theresa described the internal struggles and aspirations of her heart and her frequent mystic visions in ascetic treatises and letters, which are among the most memorable documents of the mystic literature of the Roman Catholic church, while their excellence of language and style has secured for them a place in the classic literature of Spain. Five of them are extant: Discurso ó relacion de su vida, written in 1562; El camino de la perfeccion, prepared in 1563 as a guide for the nuns of her reformed order; El libro de las fundaciones, an account of the convents founded by her; El castillo interior, ó las moradas, written in 1577, and the most celebrated of her mystic works, in which she portrays in glowing colors the gradual progress of the soul to the seventh heaven, the celestial castle of Christ, her spouse; and Santos conceptos de amor de Dios, the original of which she burned in obedience to her confessor, but which has been preserved from a copy taken by one of The original manuscripts of the first four works are preserved in the library of the Escurial. The first complete edition appeared at Salamanca in 1587, and a recent one, edited by Ochoa, at Paris in 1847 (Tesoro de las obras místicas de Santa Teresa de Jesus). A collection of letters of St. Theresa, addressed to different persons, was published at Saragossa in 1658. The abbé Migne edited a complete collection of her works in French (4 vols., Paris, 1840-'46), and they have been translated into most other European languages. A French translation from the original manuscripts was published by Père Marcel Bouix (3 vols. 8vo, Le Mans, 1852-'6). Among the many lives of St. Theresa are those of Ribera (Salamanca, 1590; French by Père Bouix, Paris, 1865), the Bollandist Vandermoere (Brussels, 1845), and Maria French (London, 1875).

the nuns.

THERESIOPEL, or Maria-Theresiopel. See Sza

BADKA.

THERMAIC GULF. See SALONICA. THERMO-ELECTRICITY, electricity developed by heat, and also the science which treats of the phenomena and mode of production. Prof. Seebeck of Berlin, in 1822, was the first to make any well directed observations upon the subject. He found that when two rods or bars of different metals were soldered together or otherwise held in intimate contact at their ends, and the junction heated, an electrical

disturbance took place, and that if the ununited ends were connected by a conductor an electric current was established. Several crystals, while their temperature is rising or falling, also become oppositely electrically excited at their opposite ends. The term pyro-electricity is usually applied to the electrical phenomena which arise from changes of heat in crystals. These phenomena were first observed in tourmaline, a double-refracting silicate crystallizing in hexagonal prisms. (See TOURMALINE.) Its electrical manifestations are confined within certain limits of temperature, chiefly between 50° and 300° F., but these limits vary with the length of the crystal. If a crystal of tourmaline is suspended by a thread at its middle, and heated, its ends will be attracted and repelled by electrically excited bodies. Many other crystals exhibit like phenomena, but less in degree, which in many cases can only be detected by a delicate electroscope. That pole of a crystal at which the algebraic sign of the change of temperature is the same as that of the electricity developed, that is to say, which manifests positive electricity when the temperature is rising, is called the analogous pole, and the other, the antilogous pole. Brazilian topaz becomes electrical when heated, the Siberian variety slightly, the Saxon not at all. When the first two are treated negative electricity appears at both ends of the crystal, while the positive is developed on the lateral faces. Pyro-electricity is chiefly developed in hemihedral crystals. The phenomena of thermo-electricity in metals is most strongly marked when two metals are heated at their junction; but if a wire of a sin. gle metal be tied in a knot, and be heated on one side of the knot, electrical disturbance will take place. When two metals are employed, the strength of the current appears to be in proportion to the difference of temperature of the two metals on each side of the junction, and its direction and also its strength upon the natures of the metals used. In fig. 1, m n represents a plate of copper, soldered on to a plate of bismuth, op, the middle of which also supports a magnetic needle, beneath the copper plate. If heat be applied at o while the axis of the instrument is in the magnetic meridian, the north pole of the needle will be deflected to the left hand of an observer looking from n to m (see GALVANISM, vol. vii., p. 592), which indicates that a galvanic current is passing through the copper from n to m. If however the junction n o is cooled, the current will flow from m to n. In the following list, according to Becquerel, the direction of the current will be from any element to any one following, the intensity being greatest between the first and the last: bismuth, platinum, lead, tin, gold,

711

FIG. 1.

silver, copper, zinc, iron, antimony. The di- | wine; boiling this to expel air, the tube was rection of the current often changes when the couple is heated beyond a certain degree. Thus, in a copper and iron circuit, the current passes from the copper to the iron through the heated part when the temperature is not higher than 570°; above this the curent passes in the opposite direction. The cause of thermo-electric currents is diversity in the molecular structure of the elements, and Becquerel ascribes them to unequal propagation of heat in the different parts of the circuit. A thermoelectric pile, or battery, in which a series of several couples are joined somewhat like the arrangement in a voltaic pile, or at least with the opposite poles of the elements in contact with each other, was devised by Nobili. A modification of this is shown in fig. 2, in which the lowest plate is bismuth, the next above antimony, the next again bismuth, and so on, the last plate being antimony. These sets of elements are arranged in a copper frame, P, in four vertical series, making in all 20 couples. The terminal plates are connected with binding screws, m and n, by which they may be connected with a resistance measurer or rheostat, or with a sine or a tangent galvanometer. (See GALVANISM, vol. vii., pp. 593-'5, and DIATHERMANOY, vol. vi., p. 81.) When the pile is composed of a great number of pairs and connected with a very delicate galvanometer, it may be used to detect the slightest changes of temperature; it is much employed in physical investigations, and will undoubtedly in time have extended practical use in physiology and medicine.

FIG. 2.

THERMOMETER (Gr. Oépun, heat, and μérpov, a measure), an instrument to measure temperatures. It is formed of two or more different substances, the volumes of which expand and contract to different extents when they are simultaneously exposed to the same differences in intensity of heat. The first attempt at indicating to the eye differences of temperature seems to have been by the contrivance variously ascribed to Drebbel of Holland and Sanctorius of Italy, about the beginning of the 17th century, and known as a weather glass. This was very rude and inaccurate, consisting of a glass bulb and tube inverted, opening below into a cup of colored liquid, which, the air of the bulb having been partly expelled by heat, rose in the tube, and stood at different heights according as the air remaining in the bulb was more or less expanded by heat. This, the origin of the common air thermometer, as improved by Boyle and by the Florentine academicians, became transformed to a smaller bulb with upright stem of somewhat fine bore, the contained liquid being colored spirits of

hermetically sealed, and the whole then affixed to a case. A scale of degrees was also introduced, its fixed points being the cold of snow or ice and the greatest heat known at Florence; it was of necessity very variable in its indications. At this stage in the progress of thermometry, much discussion in regard to the most suitable fixed points for the scale, the best substance for use in the instrument, &c., including that of the question whether water did not freeze at different temperatures in different latitudes, was carried on in England and on the continent. Hooke advocated as the lower fixed point the temperature of freezing water. Newton seems first to have discovered or taken advantage of the facts, that a thermometer placed in melting snow or ice always indicates the same temperature, and always very nearly one temperature in boiling water; but of oil, which he suggested for the liquid in the bulb, the movements were found to be too sluggish and uncertain. Römer, overcoming a prejudice that seems to have existed in regard to unequal expansion of mercury, first adopted that liquid; and he doubtless devised the instrument and scale usually attributed to Fahrenheit of Amsterdam (1720), the latter constructing and introducing the instrument, so that it became generally known throughout Europe in the first half of the 18th century. Of this thermometer, the lower fixed point, or zero, was taken at 32° below freezing point of water; but whether as the cold obtained by its maker by mixing salt and snow, or as the greatest cold observed in Iceland, and in either case as the supposed point of absolute cold, is not now definitely known; and since Fahrenheit kept his graduation of thermometers a secret, the same must be said respecting the choice of a scale of 180° between the fixed points. Celsius of Sweden (1742) introduced a scale of 100° between the fixed points; this was adopted in France at the time of the revolution, and named the thermomètre centigrade; and owing to its convenient decimal division, it has been wholly adopted in several countries of Europe, while it is coming into general use among scientific men throughout the world. For the general principles upon which the use of the thermometer depends, see EXPANSION, HEAT, and PYROMETER. -An increase in the temperature of a body is generally accompanied by an increase in its volume, and a decrease in its temperature by a contraction in its volume. Definite changes in the volume of a given substance may be used as indications of this substance having different definite temperatures, and this substance will have the temperature of the bodies by which it is surrounded, or of the medium in which it is immersed, and thus serve to measure their temperature. The substances generally used in the thermometer are glass and mercury, and the observed change of volume is the difference in the change of volume of the glass and of

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the mercury.

expels all air and moisture from the instru-
ment, which on cooling necessarily fills com-
pletely with mercury. The bulb is now placed
in some fluid heated to a few degrees above
the highest temperature which the thermom-
eter is intended to measure, and when the
mercury ceases to overflow the open end of
the tube is sealed with a blowpipe flame. In
order to graduate the instrument, the bulb and
part of the tube are surrounded with melting
ice, and when the top of the mercury column
has remained some time stationary, its posi-
tion is marked by means of a line, or a note is
made of this position, referred to the arbitrary
thermometer determined as above is designa-
ted as 0°, or zero degree, on the thermometers
known as centigrade (Celsius) and Réaumur,
and as 32° on the Fahrenheit system of grad-
uation. To determine a higher point on the
thermometer, the instrument is placed in the
interior of a metallic vessel with double walls,
between which circulates the steam from wa-
ter boiling in the bottom of the vessel. When
the top of the mercury column in the ther-
mometer has become stationary its position is
marked on the tube. The boiling point of
water is constant at the same atmospheric
pressure, and when the barometric column
has a height of 29-922 inches or 760 milli-
metres, the boiling point of water is desig-
nated as 100° on the centigrade thermome-
ter, 212° on the Fahrenheit,
and 80° on the Réaumur.
Hence, between the melting

The instrument which shows | this difference in expansions is known as the mercurial thermometer. It consists of a tube of very small interior diameter, terminating in a bulb or reservoir. The bulb and a portion of the tube are filled with mercury, and with an increase or a diminution of temperature the mercury will rise or fall in the tube; and the position of the mercury in the tube can be noted on a scale of equal parts either etched on the tube or marked on the surface or a plate to which the tube is attached. Mercury has several advantages as a thermometric substance. The successive increases in its volume for equal and successive additions of tempera-scale etched on the tube. The point on the ture, indicated by the air thermometer (see PYROMETER, vol. xiv., p. 111), are quite uniform; especially is this the case when we use the differential expansion of mercury and ordinary glass. The ordinary thermometer when constructed with care is trustworthy in the measure of temperatures up to 300° C. Up to 100° C. mercurial thermometers made of any kind of glass indicate almost exactly the same temperatures as those given by the air thermometer. Another advantage of mercury is that it does not freeze above the low temperature of -40° C., and does not boil below 360° C. But the mercury thermometer only gives accurate indications between -35° and +300° C. For temperatures above 300° C. some form of pyrometer must be used. Mercury has a low specific heat, and this property combined with its high conductivity causes it rapidly to indicate the changes in the temperature of surrounding bodies or of the medi-point um in which it is immersed.-Construction of the Mercurial Thermometer. The tube of the thermometer should be of uniform calibre throughout its whole interior. To ascertain whether this is the case, a short column of mercury is introduced into the tube; and if its length remains the same when it is moved throughout the length of the tube, we may be sure that the tube has a uniform bore, and hence that equal amounts of expansion of the mercury will cause equal additions in the length of the mercurial column in the tube. Since tubes of uniformn bore are very rare, it is generally necessary to calibrate the tube before its graduation. This is done by etching on the tube a scale of equal parts, and then, from observations on the different lengths occupied by a column of mercury which is made to pass through the tube, forming a table which gives the temperatures corresponding to the arbitrary divisions on the tube. A bulb is now blown on the tube, and this bulb and a portion of the tube are filled with mercury as follows: The air in the bulb is heated while the open end of the tube dips into mercury. The heat having been withdrawn, the air in the bulb contracts and the mercury rises in the tube and partly fills the bulb. To the open end of the tube a funnel containing mercury is adapted, and the mercury in the bulb is boiled and thus

of ice and the boiling point of water there are 100 equal degrees in the centigrade graduation, 180 in the Fahrenheit, and 80 in the Réaumur. To convert the indications of one of these thermometers into those of the other two, we have the following formula, in which F, C, and R denote equivalent temperatures expressed in degrees of Fahrenheit, centigrade, and Réaumur, respectively:

F

R

C

220

WB

80-100

210

200

90

190

70

180170

80

60

160

70

150

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F=C+32={R+32 C=R (F-32) R=C(F-32) Fig. 1 shows a thermometer graduated according to the three systems. A few weeks after a thermometer has been made and graduated it may be observed that the mercury FIG. 1.-Thermomwill not quite descend to the melting point of ice when the instrument is immersed in pounded ice. It has been found that this "elevation of the zero point," as it is called, goes on gradually for about two years after the thermometer has been con

eter with Fahrenheit, Réaumur, and Centigrade Scales.

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