Page:The New International Encyclopædia 1st ed. v. 11.djvu/21

ISOCRATES. meet all the needs of the student. There is a good English annotated edition of the Pane- gyricus by .Sandys, and selected orations have been edited with German notes by Rauchenstein- Reinhardt (lli'rlin).

I'SODIMOR'PHOUS SERIES. ' See Isomor- phism.

ISODYNAMIC (I's6-di-nam'ik) LINES (Gk. laoBimiwi, isodynaiitos, having equal power, from fffos, isos, equal + dvmfus, dynamis, power, from dvi/cur8ai, dyiiasthai, to be able). An im- aginary line on the earth's surface, such that at each point on it the total magnetic force due to the earth has the same numerical value. This force is not a 'maximum at the magnetic poles; but there are two points in the Northern Hemi- sphere and two in the Southern, called "foci,' at which the force is a maximum : that is. at each of these points the force is greater than for any point in the immediate vicinity.

ISOGAMY, i-sog'ami (from Gk. taos. inos, equal + -jdiios. fjnmos. marriage). A condition in plants in which the pairing sex-cells (gametes) are similar, that is. they show no evident distinction into male and female. Only the lowest plants are isogamous. The contrasting term is 'heterog- amy' (q.v. ). See Fertilization.

I'SOGE'OTHERMS. The name giAen to im- aginary zones beneath the earth's surface passing through points of equal temperature.

ISOGONTC (I's.Vgon'ik) LINES (from Gk. taos, isos, equal -f- yuvta, yiJiiia. angle). Lines connecting those points on the earth's surface at which the deviation of the magnetic needle from the meridian, or the so-called magnetic declina- tion, is the same. The isogonic lines, together with the isodynamie and isoclinie lines, when drawn on globes or maps, give a complete presentation of the magnetic state of the globe, as manifested at the earth's surface. These lines cover the globe in a rather irregular manner and vary in position, not only slightly from hour to hour and day to day, but qiiite appreciably from year to year, which latter changes are spoken of as the secular changes in terrestrial magnetism. A chart showing these lines will he found in the ar- ticle on SIaon'ETI.sm, Terrestrial, which should be read in this connection. See also Declixa- Tiox and Compass,

ISOGONISM, 1 sog'ij-nizm. See IsoiiORPHisM.

ISOLA BELLA, e'z6-la bel'hi. One of the Piorromean Islands (q.v,) in Lago Maggiore (q,v, ), Italy.

ISOLA isEL LIRI, del le're. A e'ty in the Province of Caserta. Italy. 9G miles northwest of Xaplc^;, on the rivers Liri (Liris) and Fibreno ( Fibrenus ). which furnish power for paper and woolen factories (Jlap: Italy, F 2). As the name indicates, the main town is on an island in the Liri, which has magnificent waterfalls 80 feet high. Half a mile beyond the picturesque es- tate of Count Balsorano are the twelfth-century Church of San Domenico and the tenth-century monastery where Gregorv VII. was once a monk. The Isola San Paolo is supposed to be the Insula Arpinas, where Cicero was born. His ancestral villa here, which in the time of Domitian be- longed to the poet Silius Italicus (q.v.), is de- scribed by him Dr l.eq. 2, ."?, Five miles west of Isola Del Liri is the thirteenth-century abbev of Santi Giovanni e Paolo di Casamari, now State property. As an example of early Gothic it is rivaled in Italy only by the Convent of Fossanova in Sonnino (q.v.). The name Casamari com- memorates the birthplace of Marius, who, like Cicero, made his home in the neighboring town of Arpino (q.v, ) — ancient Arpinum, Isola haa stone-quarries, and is lighted by electricity. Pop- ulation (commune), in 1881, 6489; in 1901, 8202. ISOLA GROSSA, gros'sa. A long and nar- row island oil' the coast of Dalmatia, Austria. Area, 35 square miles (Map: Austria, D 5). It is poorly watered, but nevertheless produces. southern fruits, such as grapes, olives, and figs. It has a population of over 3000, mostly Croats, and its chief town. Sale, has a harbor, a light- house, and a population of over 700.

ISOLA MADRE, ma'dra. One of the Borro- mean Islands (q.v.) in Lago Maggiore (q.v.), Italy.

ISOLANI, e's6-lii'ne, .Johann Ludwig Hek- TOR, Count (1.586-1040). An Imperial cavalry leader in the Thirty Years' War, born at Ciijrz, of a noljle Cypriot family. He was taken pris- oner by the 'Turks in 1602 ; and after his escape became commander of a regiment of Croats. In 1632 he was put in command of all the Croatian forces; two years later he was made Count, after deserting Wallenstein. A clever leader of light cavalry, and a terrible raider, Isolani fought in Picardy and Burgundy (1636), then in Hesse, Pomerania, and along the Upper Rhine against Guebriant.

ISOLATION (from isolate, from Fr. isoler. It. isolure, from ML, insulate, to separate, from Lat. insula, island, from in. in + salum, sea, CJk. (rdXos, salos, surge). In evolution, the separa- tion or segregation of any assemblage of plants or animals in a limited area, so that the incipient varieties or species are prevented from breeding with those of adjoining regions. Through such isolation the leveling effects of free crossing or mixing with allied varieties is prevented, llius variations or nascent species become localized, with the result that there are many thousands of local races, varieties, and species.

Besides geographical isolation, there arc other kinds of segregation. Darwin suggested two forms : ( I ) Arising from organisms breeding at slightly different seasons; (2) "from varieties of the same kind preferring to pair together." To the first of these may be added the inbreeding of butterflies of two different liroods. a part of one brood being belated and flying with their 'nephews and nieces.' See Digoxeutism.

I>amarck was the first to broach the subject of the doctrine of isolation as a factor in species- making in referring to man. Considering organ- isms in general, he points out that in reproduc- tive unions the crossings between the individuals which have different qualities or forms arc neces- sarily oppo.sed to the continuous propagation of these qualities and their forms. He then instances man, and says that, if distance of habitation did not separate men, the intermixture by generation would cause the general characteristics distinguishing difl'ercnt nations to disappear. Wagner (1868) has fully proved by numerous examples the importance of migration and isolation in species-making. See Migration, Wagner's L.^w of.

As a result of fifteen years' collecting in the Hawaiian Islands of land shells belonging mostly