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
