raiders attacked a small Federal force here in 1863. Pop. 1,669.

CORYDON, Iowa, town and county-seat of Wayne County, situated in the southern part of the State, 81 miles south of Des Moines, on the Keokuk and Western and the Chicago, Rock Island and Pacific railroads. Corydon is essentially an agricultural town and exports a large amount of timothy seed. The electric-light plant, sewer and waterworks are under municipal ownership and control. Pop. 1,703.

CORYMB, in botany, a form of indefinite inflorescence, in which the flower-stalks, though springing from different parts of the main axis, have their lengths such that their tops form a flat or nearly flat surface. Examples are meadow-sweet, hawthorn, candytuf, etc.

CORYMBUS, in ancient sculpture, the wreath of ivy-leaves, berries or garlands with which vases were encircled. The term is also applied to that style of dressing the hair among the Grecian women, in which it was tied in a knot on the top of the head. The Venus de' Medici represents the simplest form of this head dress.

CORYPHÆNA, kôr-i-fē’ną, a genus of fishes of the family Coryphanide, related to the mackerels. The body is elongated, compressed and covered with small scales, and the dorsal fin extends the whole length of the back, or nearly So. The dolphin of the ancients is the Č. hippuris. All the species, natives of the seas of warm climates, are very rapid in their motions, and very voracious. They are of brilliant colors and are objects of admiration to every voyager.

CORYPHÆUS, kôr-i-fe'ŭs, the leader of the chorus in the ancient dramas. His functions, however, were often as wide as those of our stage-manager, conductor and ballet-master. The name is now applied to the leaders of the different parts in operatic choruses, or the principal dancers in the corps de ballet. By extension it is also applied to those eminent in the arts or sciences.

CORYPHODON, kō-rif'o-don, a fossil ungulate of the extinct order Amblypoda (q.v.), found in the Lower Eocene sediments of Europe and America. The feet were short and post-like, somewhat like those of elephants, while the head resembled rather that of a hippopotamus with large flaring front teeth covered by a broad fleshy muzzle, and the skeleton had many archaic and peculiar characters. The coryphodon was the largest land animal of its time, intermediate in size between the tapir and rhinoceros. A mounted skeleton has been erected in the American Museum of Natural History, New York.

CORYZA (Gr. Kopvα, "catarrh"), a cold in the head. See COLD.

COS, or KOS, island belonging to Turkey; situated off the southwest coast of Asia Minor, in the Egean Sea; length about 25 miles; area about 110 square miles. It is noted as the birthplace of Hippocrates and Ptolemy II, surnamed Philadelphus, and it claims the honor of being the birthplace of the Greek artist, Apelles. The surface rises partly into rugged hills, but a considerable portion is fertile and well cultivated, yielding grapes, oranges, olives, pomegranates, etc. The modern town of Cos is well

built, and contains a large quadrangular fortress erected by the Knights of Rhodes in the 14th century. The harbor is now so filled up that only small vessels can enter. In the Iliad we find mention of this island as one of the allies of the Greeks. Later it was annexed to the Dorian Hexapolis. It changed hands many times until its capture by the Turks in 1523. In 1912 it was captured by the Italians but restored in the same year to the Turks with the other Ægean Islands. During the Balkan War, a movement was pushed for the union of Cos with the Greek kingdom. By the Treaty of London 30 May 1913, the final disposition of the Ægean Islands was left to the Powers; the Italian occupation of Cos continuing for the time being. In Cos was manufactured a fine, semi-transparent kind of silk, much valued by the ancients. Pop. about 10,000.

COSALITE, an important bismuth ore containing 42 per cent of that metal with formula Pb Bi S. Occurs in Colorado, Utah and Washington.

or

COSCINOMANCY, COSKINOMANCY, a kind of divination effected by means of a sieve, which was either suspended or fixed on the point of a pair of shears. The diviner then uttered a certain formula, and repeated the names of any persons suspected of a crime. If the sieve moved at the mention of any name, that person was considered guilty.

COSEGUINA, kō-sē-gwē’nä, a volcano in the western part of Nicaragua on a peninsula south of the Gulf of Fonseca. The mountain is cone-shaped and 4,000 feet high. It is remarkable on account of the eruption of 1835, beginning 20 January and lasting three days. The country within 100 miles was darkened by the cloud of ashes, and ashes were carried as far as Jamaica and Mexico. The volcano is now quiescent.

COSEL, or KOSEL, Germany, capital of a district of Silesia, Prussia, on the Oder, at the confluence of the Klodnitz, 25 miles southeast of Oppeln. It is a garrison town, has a castle, and was formerly surrounded by walls, the site of which has been converted into boulevards. A fine monument commemorates the unsuccessful siege by the French in 1807. The town manufactures celluloid, lumber, flour, malt, beer, bricks and refined petroleum. It was the capital of a former duchy in the 14th century. Pop. 7,832.

COSELEY, kōz'li, England, town in Staffordshire, within the parliamentary boundaries of the borough of Wolverhampton, eight miles northwest of Birmingham. There are iron foundries, nail, hook, chain and screw works, stove-grate manufactories, cement works, malting establishments and brick-fields. There are extensive iron and coal mines in the district. Pop. 22,834.

COSENZA, kō-sent'sä (anciently, COSENTIA), Italy, city of the southern part, capital of the province of Cosenza (Calabria Citeriore); situated on seven small hills, at the foot of the Apennines, where the Busento joins the Crati, 150 miles southeast of Naples. The metropolitan is the only church within the walls; but there are three parish churches in the suburbs. The cathedral, of the 13th century which has been restored, contains the tombs of Louis III

of Anjou and Isabella, consort of Philip III of France. In the public gardens are a figure of Liberty by Giuseppe Pacchioni, erected to those who took part in the Calabrian rebellion of 1844, and busts of Garibaldi, Cavour and Mazzini. It contains one technical school, two academies of science and fine arts and one college. The environs are beautiful, populous and well cultivated, producing abundance of corn, fruit, oil, wine and silk. It manufactures faïence, iron and steel ware. This town was anciently the capital of the Brutii, and a place of consequence in the Second Punic War. It is supposedly the burial place of Alaric, king of the Visigoths. Cosenza has frequently suffered from earthquakes, particularly in the years 1638, 1783, 1854 and 1870. Pop. about 20,000.

COSHOCTON, kō-shok'ton, Ohio, city and county-seat of Coshocton County, situated on the Muskingum River, on the Ohio Canal and on the Pennsylvania, the Pittsburgh, Chicago, Cincinnati and Saint Louis and the Wheeling and Lake Erie railroads, 69 miles northeast of Columbus. The city has four large advertising and sign manufactories employing about 1,000 hands, machine-shops, pipe works, automobile, carriage, furniture and glass factories, potteries, flour-mills, iron and steel works and a paper-mill. There is an abundant supply of gas, iron and coal nearby. There are three banks, with a combined capital of $225,000. There are four public schools, and an excellent public library, and 10 church edifices. Settled in 1811, Coshocton became a borough in 1848, and a city in 1902. Municipal affairs are administered by a mayor and council of seven members, elected biennially. The city owns and operates its waterworks. Here after a long struggle, Colonel Boquet concluded a treaty with the Delaware Indians in 1765. Pop. 10,000.

COSMATI FAMILY, a family of architects and sculptors who flourished in Rome from the last half of the 12th century to the beginning of the 14th, who are known principally through their inscriptions. The more prominent members of the family were Lorenzo (2d half of 12th century), Cosma (about 121035), Luca (1231-35), Jacopo (1231-93), Giovanni (1296 and 1303), Adeodato (1294). They won their fame by their decorative architectural work, known as Cosmati or Roman work, distinguished by the use of mosaic and colored marbles. Among their best works are the entrance to the cathedral of Civita Castellana, the cloisters of the Lateran and the abbeyhouse of Saint Pool; the door of Saint Saba; choir-screen in Saint Lorenzo fuori le Mura; tombs in Santa Maria sopra Minerva, in Santa Maria Maggiore and in Santa Balbina; the chapel of the Sancta Sanctorum in the Lateran; the marble altar at Saint Cesareo and the magnificent cloisters at Saint Paolo fuori le Mura. A large number of unsigned works by members and pupils of the same family are to be found in Rome. They are mainly minor pieces: baldacchini, candlesticks, tombs, etc., all remarkable for their exquisite sculpture and beautifully decorative mosaics. Gothic lines predominate in their style, but the defects of the execution of detail were offset by the beauty of their materials. Consult Boito, 'Architettura del medio evo (Milan 1880); Müntz, E., 'Etudes sur l'histoire des arts à Rome pendant le moyen

COSMETICS (Gr. κοσμητικός, from κοσμεῖν, "to decorate"), means for preserving or increasing the beauty of the human body. Such means are used by the most savage as well as the most civilized nations. Cosmetics consist of perfumed waters, oils, salves and powders and are applied to various parts of the body, the face, hair, teeth and hands. Their purposes are to add or change color, to remove blemishes, whiten teeth, perfume the breath or deodorize any offensive natural odors and stimulate growth of hair. Most of the powder preparations for the skin are injurious for they often contain poisonous substances and clog the pores of the skin, thus interfering with its natural functions. Excessive use of creams serves to enlarge the pores of the skin and make it wrinkle early. Manicuring and hair-dressing belong to the cosmetic art. Cosmetic surgery is practised to remove positive disfigurements, such as birthmarks, moles, harelip, superfluous hairs, etc. Consult Peisse, G. W. S., 'Des odeurs, des parfums, et des cosmétiques (Paris 1856; Eng. trans., Philadelphia 1857); Hirzel, "Toilettenchemie' (Leipzig 1874) Koller, Thomas, Cosmetics: a Handbook of the Manufacture, Employment and Testing of All Cosmetic Materials and Specialties (trans. from the German by Chas. Salter, London 1911).

COSMIC DUST. See DUST. COSMICAL GEOLOGY, or COSMOGONY, that branch of geology that treats of the origin of the earth and its relations to the rest of the solar system and to the universe in general. See COSMOGONY, and the section on Cosmogony in the article on GEOLOGY.

COSMOGONY. From the Greek коoμoyóvia, meaning creation of the world. It is authenticated by Philolaüs and Plutarch that Pythagoras himself used the word kooμos, to denote the order of the world, to which is added yevía, origin; the word Kooμоyóvia being first used as the title of a work by Parmenides (born 544 B.C.) who was the revered teacher of Plato. The term is now used to designate theories in regard to the origin and development of the solar and stellar systems, and the universe in general.

From the earliest ages the subject of cosmogony has been considered so important for human thought that, by way of poetry and allegory, it usually enters into the religious teachings of the different peoples, as the Greeks, the Hebrews, Egyptians, Persians and Hindus; in fact, it is almost as prevalent among primitive races as mythology and folklore, with which, in early literature, it is usually connected. The cosmogony of the Book of Genesis may be considered the most advanced development of Hebrew thought, as modified by the learning of the Chaldeans and Egyptians.

Among the Greeks cosmogony was first treated by the poets in a very primitive manner, and afterward developed into more of a science by the natural philosophers, such as Thales, Anaximenes, Anaximander, Xenophanes, Parmenides, Empedocles, Anaxagoras, Plato and Aristotle. The highly artistic doc

trine set forth in Plato's Timaeus probably represents the highest development of Greek thought on this subject, though from a modern point of view the theories of the school of Atomists, founded by Leucippus and Democritus, are the most interesting because they predicted the development of vortices such as we find among the spiral or whirlpool nebulæ, disclosed by modern astronomical observations. Thus the Greeks were the first to attempt to explain the origin and motions of the heavenly bodies, and how these motions originated; and we shall therefore pass over the other early writings, and notice only the cosmogony of the Greek Atomists, since this alone approaches the requirements of modern astronomy.

In his Outlines of the History of Greek Philosophy, the late Prof. Edouard Zeller, of the University of Berlin, summarizes the views of the Atomistic School thus: "On account of their weight, all the atoms from eternity move downward in infinite space; but according to the Atomists, the larger and therefore heavier atoms fall more quickly than the smaller and lighter, and strike against them; thus the smaller are impelled upwards, and from the collision of these two motions, from the concussion and rebound of the atoms, a whirling movement is produced. In consequence of this, on the one hand the homogeneous atoms are brought together; on the other, through the entanglement of variously shaped atoms, complexes of atoms, or worlds, segregated and eternally sundered, are formed. As motion has no beginning, and the mass of atoms and of empty space has no limits, there must always have been innumerable multitudes of such worlds existing under the most various conditions, and having the most various forms. Of these innumerable worlds our world is one." (Cf. Zeiler's 'Outlines, p. 79).

The theory of the Atomists here set forth is erroneous in ascribing the collisions to the more rapid fall of the heavier atoms; yet this accorded with the teachings of physics coming down from the time of Aristotle. This fallacious doctrine was first overthrown by Galileo's discovery of the true law of accelerative force, under which heavy and light bodies fall with the same velocity. Leaving out of account this defect in physical theory, the Greek explanation of the origin of vortices is clear and is the first attempt of scientific character at explaining the motions of rotation and revolution noticed among the heavenly bodies.

DEVELOPMENT OF THE SOLAR SYSTEM.

Laplace's Nebular Hypothesis.- Not long after Galileo's invention of the telescope in 1610, and its application to the heavens by his immediate successors, it was found that the Sun and Mars were rotating on their axes, that Jupiter had equatorial belts and a system of four satellites whirling about that great planet, and that the planet Saturn was surrounded by the system of rings. The rotation of the earth on its axis had been taught by Aristarchus of Samos (who flourished about 270 B.C.), and was fully established by the great work of Copernicus, published in 1543. Similar rotatory motion of the other planets was now proved by the telescopic discoveries of Galileo. So many motions of rotation and of revolution naturally increased the complexity of the system of the

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world; and when philosophers began to cast about for the cause of these things, Kepler suspected that the rotation of the sun had some influence on the orbital motions of the planets. In fact, he thought that subtle spirits emanating from the surface of the sun had impressed themselves on the motions of the planets, so that they were carried around tangentially in the same direction. This is the earliest hint of the theory afterward developed by Kant and Laplace under the name of the nebular hypothesis." The term nebulæ designates patches of luminous matter occurring in the sky and differing from the stars in that they present large surfaces of varying brilliancy instead of small definite points of light.

We shall not go into the details of the early history of the nebular hypothesis, beyond remarking that in various forms it was imperfectly outlined by Emanuel Swedenborg (16881772); more satisfactorily treated by Thomas Wright (1711-86), of Durham, England; Immanuel Kant (1724-1804), of Königsberg, Prussia; and finally put on a much more scientific basis by the telescopic explorations of Sir William Herschel (1738-1822), and the mathematical genius and dynamical judgment of the great French astronomer Laplace (1749-1827). Swedenborg's Cosmogony was the earliest, 1734. Wright's work dates from 1750; Kant's from 1755, and he acknowledges his indebtedness to Wright; Herschel's from 1791, after years of mature observations on nebulæ; while Laplace's theory of 1796 was the outcome of a quarter of a century of profound study of the mechanics of the solar system.

On account of the great mathematical prestige of the illustrious author of the 'Mécanique Céleste, it was natural that Laplace's theory should be the one most generally accepted by men of science. According to this view the matter now constituting the sun and planets was originally diffused into an oblate planetary nebula. Sir William Herschel had recently observed and catalogued great numbers of planetary nebulæ throughout the sidereal universe. To account for the motions of the planets close to one fundamental plane and in nearly circular orbits, Laplace conceived that the primordial nebula had been endowed with a rapid motion of rotation; and when thus rendered very oblate by the effects of centrifugal force, had detached or thrown off successive rings of vapor from the equatorial portion of the mass, which was supposed to be at high temperature and kept in equilibrium under the pressure and attraction of its parts. These rings of vapor were imagined to have condensed into the planets, which therefore revolve in nearly circular orbits. The satellites were explained in the same way, by the condensation of rings of vapor imagined to have been thrown off from the several planets, as they cooled and contracted and accelerated correspondingly their velocity of axial rotation.

In very brief outline this is the celebrated nebular hypothesis of Laplace, which has exerted so great an influence on philosophic thought for more than 100 years. In some form or other it enters into all the books on astronomy, as giving the best available explanation of the origin of the solar system; but it will be shown below that the "hypothesis of detachment" postulated by Laplace is entirely er

roneous, and will have to be supplanted by a very different theory.

Before considering certain grave errors in the theory of Laplace, it may be remarked that Sir Isaac Newton had given much thought to the motions of the planets and satellites, especcially remarking on the beautiful, orderly and symmetrical arrangement of the solar system; but he was unable to explain the orderly movements of these bodies, except by supposing that they had been set revolving in their orbits by the immediate hand of the Deity. Laplace's theory had the great advantage, from a scientific point of view, that for a teleological it substituted a mechanical explanation of the motions of the planets, in harmony with Herschel's observations of the nebula. Notwithstanding the fundamental error involved in the theory of detachment, the nebular hypothesis as a whole has guided our thought pretty much up to the present time. Yet the difficulties encountered by the theory of Laplace have steadily increased, and of late years became so overwhelming that the old conceptions of rings detached by rotation have had to be entirely abandoned.

As the solar system was held to have resulted from the condensation of a globular or planetary nebula, the subject of the nebular hypothesis is closely connected historically with the gravitational theory of the sun's heat. For a long time it was assumed by investigators that the sun was originally expanded into a nebula filling the planetary orbits, and rotating in equilibrium under the hydrostatic pressure and attraction of its parts. In order to keep this figure of equilibrium the temperature would have had to be enormous, and such a temperature really could not be maintained, owing to the extreme tenuity of the hypothetical nebula. For when the nebula extended to Neptune's orbit the average density would be 260,000,000 times less than that of atmospheric air at sea-level; and such a tenuous medium could exert no hydrostatic pressure from the centre outwards, for detaching the planets by increase of centrifugal force under accelerating rotation, as imagined by Laplace. This criticism against Laplace's theory was urged by Kirkwood and Peirce over 40 years ago, and such an objection is valid and convincing; but as there was no other suggested way in which the planetary bodies could be started revolving in their nearly circular orbits, it was not doubted that such detachment had occurred.

In 1861 the French physicist, Babinet, pointed out a fatal weakness of Laplace's theory which is now usually known as "Babinet's criterion." It is based on the mechanical principle of the conservation of areas, so much applied by Laplace and other investigators since Newton's proof of the constancy of the areas described by any system of particles contracting and accelerating its rotation under central forces. It readily follows from this principle that whatever changes may take place in the system, its whole quantity of rotation must remain constant; by this is meant that if the mass of each particle of the system is multiplied by the square of its distance from the central axis of rotation and also by its angular velocity, and if all the products thus obtained for the particles are added together, the sum will remain forever constant. Now it is possible to obtain

a quite approximate value for this sum derived from the actual system as we see it today, for the masses of its various parts, their distances from the central axis, and their observed angular velocities of motion are all known. Having found this quantity, we may proceed to test the Laplacian hypothesis in a great variety of ways, many of which lead to necessary assumptions which are not only quite incredible, but in some cases impossible.

For example, we may readily determine the period of rotation of the solar nebula when it extended outward to each of the planets successively; by so doing we obtain the results given in the following table:

Table showing the application of Babinet's criterion to the planets and satellites, when the Sun and planets are expanded to fill the orbits of the bodies revolving around them

It will at once be noticed how greatly the numbers of the third column exceed those of the second. Should we suppose that Neptune, for example, could have been formed in this way it would be necessary to assume that the period of its ring was diminished from nearly 3,000,000 to but 165 years, notwithstanding that we can recognize no imaginable cause which could produce this diminution.

Babinet's criterion furnishes us with several other tests, some of them even more conclusive than this, of the impossibility of the material from which the planets are formed having been abandoned by the original nebula in the form of rings. If, overlooking these, we admit that a ring were abandoned, it can be shown that so far from the material of the ring ultimately being gathered into a single mass, the tidal action of the central portion of the cloud would separate and scatter it, so that a ring would not even start to gather into a planet. But further than this, it can be shown that even if the greater part of the ring could be gathered into a single planet, it would be quite impossible for this mass to gather to itself the remaining parts of the ring.

We have thus considered the Laplacian hypothesis somewhat fully because of its historical importance and because for so long a time it was regarded as furnishing a very probable outline of the successive steps by which our solar system developed from the original nebula into its present form. It should not be overlooked, however, that much less importance was ascribed to this theory by its originator than by his followers, who, attracted by its completeness and seeming simplicity, raised it almost to the position of a proved and fundamental doctrine.

Laplace himself, a master of rigorous mathematical deduction, could not have been deceived as to the weakness of its foundation. Indeed, he put it forth as a speculation merely, which (in his own words) was advanced "with that distrust which everything ought to inspire that is not a result of observation or of calculation."

The

Modern Hypotheses.— In all modern hypotheses as to the development of the solar system it is recognized at the outset that the original nebula must have been of a very heterogeneous structure. Its material in the beginning may have been arranged in a more or less spiral form, the curved branches extending outward from a common centre, and thus resembling the thousands of spiral nebulæ seen in the sky, but whether this be so or not, it is assumed that there existed here and there throughout the cloud many smaller clouds, or knots, of the nebulous material, denser than the nebula immediately surrounding them. The original nebula is supposed to have been a great cloud, composed of meteorites or meteoric particles, cosmic dust, gases, and probably some matter in a radiant condition; in short, to have had exactly the same constitution as we believe is possessed by the same class of nebula which we see in the sky. The whole meteoric cloud thus constitutes a Resisting Medium, through which its separate particles and the denser clouds within it must necessarily move. question concerning what such a heterogeneous cloud will develop into as it shrinks together under its own gravitation has recently received a great deal of attention from certain astronomers. The result of a most thorough mathematical analysis is to indicate that the outcome must be a solar system more or less closely resembling our own. The analysis has been applied, not only to a broad outline of the development of the system as a whole, but also to the separate planet-satellite systems, the rings of Saturn, the retrograde or apparently too rapid motions of certain satellites, and even to the reason for the present situations and rotations of the planets, for all of which it seems to account in a satisfactory manner. The principal contributions to this subject will be found by the reader as follows: Thomas C. Chamberlain and F. R. Moulton, Year-book No. 3 of the Carnegie Institution of Washington; The Astrophysical Journal (Vol. XXII, 1905); See, T. J. J., 'Evolution of the Stellar System' (Vol. II, Lynn, Mass.), and numerous papers in the Astronomische Nachrichten and the Journal of the American Philosophical Society. By the former authors, the new theory is called the Planetesimal Theory, the separate particles of the original nebula being called Planetesimals; by the latter it is named the Capture Theory, attention being thus drawn to the fact that the lesser bodies of the completed system, instead of having originally formed a part of the central body and having afterward separated from it, were actually drawn nearer to this body from without, and so in a sense "captured." In the present article we can only indicate in briefest outline the successive steps of the development which the original nebula will undergo.

In the first place, any separate particle or any cloud of particles in the original nebula will (unless there is no motion at all) find itself moving, not in empty space, but in a re

sisting medium. It can readily be shown by mathematics that the certain effect of this resistance will be to cause the particle to fall continually nearer the centre of the whole, gathering up and adding to itself much of the material through which it moves, until finally, if the resisting medium extends quite to the centre, the particle or cloud will fall onto the central mass and become a part of it. Thus the central mass will continually grow by the absorption of a great part of the cloud around it, nor will this action cease until the resisting material has been quite completely swept away.

There will thus come a time when the nebula has been replaced by a dense, central, nebulous mass, around which a greater or less number of smaller clouds or swarms are revolving in a region which still contains a considerable amount of resisting material. And these smaller clouds will all move around the central cloud in the same direction, which will be that of the general rotation of the original nebula as a whole, for it can be shown that such bodies as began to move in a contrary direction, when the resistance was high, must have been speedily brought down upon the central mass. Investigation shows that a second effect of a resisting medium must be to diminish the eccentricity (or increase the roundness), of the paths in which the bodies are moving. Thus the lesser clouds must steadily drop nearer the centre, their orbits at the same time becoming continually rounder, until they attain a region which has been swept clear, or nearly so, of resisting material. The contraction of each smaller cloud into a planet with a possible system of satellites is explained by an exactly similar course of reasoning.

It is thus from the lesser clouds, or portions of greater condensation in the original nebula, that the planets have originated, and each has acquired a greater or less size according as its cloud in passing through the resisting medium has gathered up and added to itself a greater or less amount of this material. It can be shown that in whatever manner a small cloud may have been originally rotating, the effect of its collisions with the scattered particles among which it moves will be to give it a forward rotation; that is, one in the same direction as its own motion around the central mass. And the more collisions it has sustained, and hence the larger it has grown, the more rapid should we expect its rotation to become. This is in accordance with what is observed in the solar system, where Jupiter and Saturn rotate in less than half the time of the small planets. A similar investigation shows that all satellites formed near the smaller clouds while the system was still young should have small and rounded orbits, and their motion should be direct, but that there may also be more distant satellites moving in a retrograde direction in orbits which are highly eccentric.

The Origin of Spiral Nebulas.— A theory has been advanced, and quite fully developed from a mathematical standpoint, to account for the existence of spiral nebulæ in general, and in particular for that of the original solar nebula, which is thus supposed to have had a spiral form. It is supposed that these nebulæ were caused by the close approach, or even by the actual collision, of two suns, for it can be shown that if such a close approach occurs the