of 1557. Newton succeeded in demonstrating that they are guided in their movements by the same principle which controls the planets in their orbits; and Halley was the first, by determining the parabolic elements of a number of comets from the recorded observations, to identify the comet of 1682 with one which had been observed in 1607 and the observations recorded by Kepler and Longomontanus, and also with a comet observed in 1531 by Apian, at Ingoldstadt, and thus confidently to predict the return at the end of 1758 or beginning of 1759, of a comet which would have the same parabolic elements. These parabolic elements are elements of a parabola nearly coincident with the elongated elliptic orbit of the comet. They are (1) The inclination. (2) The longitude of the node. These two determine the plane of the orbit. (3) The longitude of the perihelion, or point of nearest approach to the sun. (4) The perihelion distance, or nearness of approach to the sun. (5) The time of perihelion passage. (6) The direction of motion, whether direct or retrograde.

The

To determine these parabolic elements, three observations of the comet are sufficient; and by a table of such elements deduced from the recorded observations, it is possible at once to ascertain whether any newly observed comet is identical with any that have been previously observed. To predict, however, with accuracy the time of the return of a comet, a much more elaborate calculation must be made of the orbit, taking into account the perturbations of the planets to whose influence it is subject. This difficult problem was solved, in the case of Halley's comet, by the joint work of Laland, Madame Lepante, and Clairaut, who announced, in November 1758, just as astronomers began to look out for the return of the comet, that it would take 618 days more to return to the perihelion than on the preceding revolution. The perihelion passage was fixed about the middle of April 1759; but Clairaut distinctly forewarned the world that, being pressed for time, he had neglected small values, which collectively might amount to about a month in the seventy-six years. comet passed the perihelion on the 12th March 1759, exactly a month before the time announced, but within the assigned limits of divergence from that date. The elements of its orbit proclaimed it to be the comet of the former periods by their similarity. For the next perihelion passage, the different calculations executed by MM. Damoiseau, Rosenberger, Lehmann, and De Pontécoulant, fixed respectively the 4th, the 26th, the 11th, and the 13th November 1835. Subsequently, observations indicated the 16th-that is to say, a deviation of only three days from what turned out the most accurate calculation, and a deviation of twelve days from the most remote. We have adverted to the perihelion passages of this comet in 1531, 1607, 1682, 1759, and 1835. It is also now identified with a comet observed in 1456, and one in 1378, recorded by Chinese observations. There are no sufficiently reliable European observations previous to 1456, but it is conjectured by Arago that this comet is the same with the comet of 1305; that of 1230; a comet mentioned in 1006 by Hali Ben Rodoan; that of 885; finally, a comet seen in the year 52 before our era.

This account of Halley's comet has been given at length to illustrate the principles on which the calculations are made. A simple method, due to Olbers, enables the elements of cometary orbits to be calculated in a comparatively short time, and almost all comets discovered have now their paths roughly determined soon after they become visible. There are two other periodical comets of peculiar interest (1) That of Encke, with a short period of 1204 days. Its orbit does not extend so far as

the orbit of Jupiter, and a slight acceleration in its periodic times of return was regarded until lately as suggesting the possibility of the space, within our solar system at least, being occupied by a resisting medium, though of extreme rarity. (2) That of Biela or Gambart, having a period of six years and three-quarters. During the visit of this comet in 1846, it was seen first at New Haven, U.S., by Messrs Herrick and Bradley, on December 29, 1845, in the act of separating into two distinct comets, which kept moving side by side till they disappeared. On the return of the comet in the autumn of 1852, the distance between the two nuclei had much increased. Since then, although repeatedly due, it has not again been seen.

ORBIT

Jan.25

Jan. 5. 1681 OF THE EARTH

The celebrated comet of 1680, which furnished Newton with the occasion for proving that comets revolve around the sun in conic sections, and that, consequently, they are retained in their orbits by the same force as that which regulates the movements of the planets, appears to have been about the most remarkable for brilliancy of any of which we have authentic accounts. This comet is sup posed to be identical with the one that appeared about the time of Caesar's death (44 B.C.), with that which was seen in the reign of Justinian in the year 531, and with another in the year 1106, in the reign of Henry II., the period of revolution, according to the orbit_calculated for it by Whiston, being about 575 years. There is, however, some doubt among astronomers as to the real form of its orbit, the one assigned to it by Encke giving it a period of 8813 years. This comet approached nearer to the sun than any known, except that of 1843. The comet of 1680 approached the

Nov. 17 1680

Νοτ. 213

Dec. 29

Dec 21

Nov. 25

Dec12

SUN

sun within the 163d of the semi-diameter of the earth's orbit. The annexed diagram shows a part of its path; the same diagram shows the direction

of the tail.

In the first half of the 19th century, the comets chiefly notable are those of 1811 and 1843. The former was a most brilliant object for many weeks in the northern heavens. It is periodic, though travelling at aphelion to the enormous distance from the sun of 40,121,000,000 miles. The latter was also remarkable for its brilliance, but chiefly for its very near approach to the sun, passing so near that a trifling change in its direction of approach would have caused a collision. Not more than 32,000 miles separated their surfaces when nearest. Its tail also was enormous, reaching in length 200,000,000 miles. Since 1850 many brilliant comets are recorded: Donati's in 1858; and the great comet of 1861, through the tail of which our earth passed on June 30th of that year,

with scarcely a sign observable of the passage; also Coggia's comet in 1874, remarkable for the series of envelopes of luminous matter which seemed to combine to form its tail. The great comet of 1880 astonished astronomers by following the same track as that of 1843, almost grazing the sun. That of 1881 iii followed the track of that of 1807, for a return of which it was at first mistaken. These two examples demonstrated that in some cases several comets travel on the same orbit, at great distances, however, from one another. The comet 1881 iii was the first successfully photographed, Janssen obtaining a picture including 2, and Dr Henry Draper of New York one including 10°, of its tail. Dr Huggins and Dr Draper were also both successful in photographing its spectrum, with results confirming what eye observations already had revealed. Dr Schäberle at Ann Arbor, Michigan, discovered another bright comet, the fourth for the year 1881, which for a time accompanied 1881 iii, both being in the northern heavens together. At Dudley Observatory, U.S., a comparatively small comet was discovered soon after by Mr Wells, remarkable as the first in whose spectrum the sodium line was seen. In 1882 the surprise of 1880 was repeated. Another bright comet appeared in September, following the tracks of the 1843 and 1880 comets, making the third in an orbital procession in space. It was seen in New Zealand on September 3, at the Cape of Good Hope on September 8, and at Rio de Janeiro on the 11th. Mr Common at London had been seeking for a short time to catch a bright comet near the sun in the daytime. Independently, on September 17, he discovered this one, close to and rapidly nearing the sun. Clouds prevented him from seeing the passage, but it was observed at the Cape of Good Hope by Messrs Finlay and Elkin, who were watching at the time. Passing in front of the sun, it disappeared from view, overpowered by the solar brilliance, to reappear shortly passing off the other edge of the disc. All next day it was clearly seen, only surpassed in brilliancy by the sun itself. Though it had passed so close to the sun, it experienced no retardation of speed, proving that very near the solar surface there can be no resisting medium of density to affect such a body. It was followed with the telescope to a distance from the earth of 470,000,000 miles. This long observation enabled its period to be well ascertained as about 700 years. It exhibited in a marked degree a tendency to disruption. 'Space appeared, says Miss Clerke, to be strewn with the filmy debris of this extraordinary body all along the track of its retreat from the sun. Its tails corresponded to types 1 and 2 (see post), and there was a vast outburst of luminous matter in October towards the sun, having a diameter of 4,000,000 miles. Its spectrum showed the sodium line in addition to the usual cometary bands. The year 1883 was barren in cometary results; 1884 saw three new comets discovered respectively in Tennessee, Australia, and Europe by Barnard, Ross, and Wolf. In 1885, on the 27th November, there was a grand display of the meteors into which Biela's comet is now generally considered to have broken up; 50 to 60 a minute being recorded. Brooks, of Phelps, New York, discovered a comet on August 31 in that year. But in the next year (1886), within two months, three comets

377

rewarded this diligent observer, a record equalled in 1887 by Barnard, of Nashville, Tennessee. In 1888 comets were discovered by Sawerthal on February 18, and by Brooks, New York, on August 7. The returns of Encke's comet and of Faye's comet also marked that year, as they again did the year 1895, in which De Vico's comet was seen for the first time since 1844. Seven new comets were seen for the first time between Nov. 1895 and Nov. 1896.

Comet of 1811.

The quantity of matter in even the largest comet is known to be very small, or so of that of the earth in a calculated instance, much less probably in many others. The nucleus, in which most of this is contained, is generally admitted to be a more or less close congeries of meteoric fragments. This is shown by the smallness of its mass as compared with its size, its spectrum, and the fact that comets and meteors follow one another in similar orbits.

Donati's Comet, 1858.

Biela's lost comet is now probably scattered into the meteor stream which pursues its track (see ante). The close agreement of cometary and meteoric orbits may appear from the fact that Tempel's comet (1866) has a period of 33-28 years, and the three groups of November meteors, following the same line, periods respectively of 32-25, 33-31, and 33:11 years. Also just as these groups follow one another in procession round the sun, so do the comets above mentioned of 1843, 1880, and 1882. Other systems of mingled comets and meteors are also known, and the spectroscopic researches of Lockyer may be said to have demonstrated that the peculiar spectrum of comets can be produced from meteors. Carbon, hydrogen, and sodium have been shown to enter into the composition of cometary nuclei. A banded spectrum of a hydrocarbon is the usual type, the sodium line only showing when the nucleus is close to the sun, and sweeping rapidly past it in a state of great disturbance. Usually as the nucleus nears the sun, it appears disturbed; then jets or masses of luminous material, gas or fine dust, are thrown up. Some repulsive force appears to seize these and

sweep them out into space with enormous rapidity, producing the splendid phenomena of the tail. The researches of Olbers, Bessel, Norton of Yale College, U.S., C. F. Pope, Zöllner, and especially Professor Bredichin, late of Moscow Observatory, have gone far to establish the existence of this force, and to identify it with electric repulsion. Professor Bredichin has divided comets' tails into three classes, those of hydrogen, of hydrocarbons, and of iron, due respectively to a repellent force (1) of 12 times solar gravity, (2) equal to it, and (3) of it. The first material and force give straight, the second slightly curved, and the third strongly curved tails. The comet, 1886 f, showed three tails, one corresponding to each of these types. Observation and calculation have verified these conclusions as to the forces, and forms of tails, but not yet as to the electric nature of the forces. The light of comets is mainly due to electric discharges; a part, however, is reflected solar light, and a part perhaps due to incandescence. The tenuity of comets' tails is inconceivable to us, stars, which the slightest fog would conceal, shining clearly through a thickness of millions of miles of their material. Hence, although so great a display is caused by the matter swept away from the comet at perihelion, it loses but little in apparent bulk, though in the course of centuries the loss is abundantly perceptible. Some comets, Professor Kirkwood suggests, are probably asteroids, thrown out of their proper track by the disturbing force of Jupiter.

pro

Comets have been alternately regarded with terror and with welcome in the popular mind. The appearance of Halley's comet in 1456, just as the Turks had become masters of Constantinople, and threatened an advance into Europe, was regarded by Christendom with a superstitious dread, and to the Ave Maria was added the prayer: Lord save us from the devil, the Turk, and the comet.' At Constantinople the occurrence of a lunar eclipse at the same time increased the portentousness of the event. The discoveries of science of the magnitude of the space filled by their bodies, and their digious velocity, together with the confessed impossibility of always predicting their approach, produced fears of another kind, which have sometimes been, especially in France, extravagantly exaggerated in the public mind. The groundlessness of such alarms, from the extreme improbability of collision with the nucleus, the innocuousness of a contact with the extremely attenuated surrounding matter, and, possibly, to the greater part of the world, of a collision with the nucleus itself, will be sufficiently evident from what has been said above. It is certain that already, on many occasions, some of the attenuated vapour in the tail of comets must have come within the earth's attraction, and been absorbed in its atmosphere. Whether the effect is deleterious or salubrious, or whether it has any perceptible influence at all, is only matter of speculation. The salubrity of cometary influence is now a popular idea; and the vintages of 1811 and 1858 were favourable seasons, whose produce has been advertised as the comet wines. It is scarcely worth while, however, to follow further speculation on these subjects, and it has been considered preferable to confine this article chiefly to the description of the general characteristics of comets, and the facts respecting them afforded by science.

Comfrey (Symphytum), a common palæarctic genus of Boraginaceae, somewhat coarse perennial herbs, although occasionally to be seen in flowerborders. S. officinale (blue) and S. tuberosum (yellow) are frequent in shady and moist places. S. officinale was formerly much esteemed as a vulnerary. Its young leaves and its blanched shoots are still occasionally used as boiled vege. tabies. The Prickly Comfrey (S. asperrimum),

COMINES

a native of Siberia, 6-10 feet in height, has been recommended for feeding cattle. The stamens are covered in this genus by five awl-shaped processes pushed in from the outside of the corolla, and meeting so as to form a false bottom impassable to ants, flies, and other small honeythieves, but which can be thrust aside by the

Comfrey (Symphytum officinale).

humble-bees

which alone fertilise the flower. Many bees, however (especially B. terrestris and one or two others), prefer to bite a hole in the side of the corolla below this cover, and the flowers may thus be seen to be visited both in the legitimate and illegitimate way. See, under FLOWER, Fertili sation of the Flower, vol. iv. p. 692.

Comines, a town on the borders of Belgium and France, 15 miles SW. of Courtrai by rail, divided by the Lys into two parts, of which that on the left (pop. 4381) belongs to Belgium; the other, on the right (pop. 6355), to France. The town has some manufactures, and was the seat of the family of Comines.

Comines, PHILIPPE DE, Sieur d'Argenton, a French statesman and historian, who was born about 1445-at Renescure, in the neighbourhood of Hazebrouck. His ancestors had been citizens of Ghent. He joined the court of Burgundy, and was sent by Charles the Bold on important missions to France, England, and Spain. In 1472 he forsook Charles and entered the service of Louis XI. of France. He was rewarded with the rich fief of Talmont, and became one of Louis's most trusted advisers. On the accession of Charles VIII. he was deprived of Talmont, and cast into prison for having incurred the displeasure of the regent, Anne of Beaujeu. He accompanied Charles VIII. on his Italian expedition, was present at the battle of Fornovo, and had an interview with Machiavelli in Florence. He held sundry places and pensions under Louis XII., and died in 1509. His Mémoires consist of seven books, six of which deal with the reign of Louis XI., while the seventh treats of Charles VIII.'s wars in Italy. They are the earliest example in

COMISO

French literature of the history as distinguished from the chronicle. Unlike the chroniclers, Comines cares little for the mere spectacle of courtly and military life. His sympathies are with the king against the nobles; his interest is centred in statecraft; he takes a keen delight in seeing the game of politics well played. His reflections on men and affairs are always dispassionate, and often pregnant and acute. His Lettres et Negotiations were published in 1867-68. The best edition of the Mémoires is that by Chantelauze (Paris, 1881). The English translation by Danett (1596) was re-edited by Whibley in 1897.

Comi'so, a town of Sicily, 37 miles WSW. of Syracuse, with manufactures of soap and pottery. Cotton is largely grown here. Pop. 19,333.

Comitia were the legal or constitutional meetings of the Roman people, convened by a magistrate, usually for the purpose of putting a question to the vote. According to the constitution of the several gatherings, they were comitia curiata, comitia centuriata, or comitia tributa respectively. See ROME. Comity of Nations-more frequently mentioned by its Latin equivalent, comitas gentium is the international courtesy by which effect is given to the laws of one state within the territory and against the citizens of another state. In the silence of any positive rule,' says Story, 'affirming, or denying, or restraining the operation of foreign laws, courts of justice presume the tacit adoption of them by their own government, unless they are repugnant to its policy or prejudicial to its interests.' See Story's Conflict of Laws; and INTERNATIONAL LAW.

Comma, in the mathematical study of sound, is a small interval, generally corresponding to the vibration-ratio 81: 80, which occurs between the true pitches of two notes, which on the piano, organ, and other tempered instruments, are represented by one only. See TEMPERAMENT.

manding in chief. In 1887 the title of commanderin-chief was revived; and in 1895 (on the resignation of the Duke of Cambridge) effect was given to the recommendations of the Hartington Commission, by a more perfect organisation of our national defences under one supreme authority-though nominally since 1855 the commander-in-chief has been strictly subordinate to the Secretary of State for War. His office, technically called the Horse Guards, is the military department of the War Office (q.v.). At its head is the adjutant-general, and its several branches are presided over by the quartermaster-general, the military secretary, the inspector-general of fortifications, the directors of artillery, of military intelligence, of the army medical department, and of military education, the chaplain-general, and the principal veterinary surgeon. All promotions and military appointments are recommended by the commander-in-chief, those of great importance being supervised by the war minister, and, if necessary, discussed by the cabinet. He is responsible for recruiting operations, the technical education of officers and men, and everything connected with the efficiency, distribution, and mobilisation of the troops, together with the construction and armament of fortifications. He exercises an inspectional control over the men who are under the immediate command of the general officers commanding the various districts. See WOLSELEY.

There is also a local commander-in-chief in India, under whom all the forces there are placed, and in many of the colonies the governor bears this title. It would also be given to the officer in command of any large army engaged in active operations. The powers of these officers extend only to those troops that may be placed under them by orders from the commander-in-chief at the Horse Guards.

A naval commander-in-chief is the chief admiral at any port or station. In the United States the president is ex officio the commander-in-chief of the army and navy.

Commandery, the district under a commander, specially used in connection with the Templars (q.v.), the Hospitallers (q.v.), and other religious orders.

Commander, in the British navy, is an officer next under a captain in rank, and serves either as second in command in a large ship, or in independent command of a smaller vessel. In matters of etiquette, he ranks with a lieutenant-colonel in the army, but junior of that rank; and he bears the title of captain by courtesy. There were, in 1888, 160 commanders employed, with pay of £1 per day; while there were 69 on half-pay, but eligible for re-employment, and 347 on retired pay; but the whole list of those employed, or eligible for employment, is to be raised to 270. Retirement is optional at the age of forty-five; and compulsory at fifty, or after five years without employment. In the United States navy, commanders have a rank next below that of captain, and next above that of a lieutenant-commander, and rank with lieutenant-colonels in the army.

Commander-in-chief is the highest staff appointment in the British army. After the death of the Duke of Wellington in 1852, this title, which had been borne by him for many years, was allowed to lapse, and the administration of the army was placed under a general on the staff who was styled the general (or field-marshal, if of that rank) com

Commandite, SOCIÉTÉ EN, or PARTNERSHIP IN, an expression used for at least two centuries in France, to express a partnership in which one may advance capital without taking part in the manage

with the business. The term 'sleeping partner' used in this country would nearly express the same idea, were it not for the attendant unlimited liability. The phrase is derived from the old meaning in the commercial nomenclature of France of the word commande, which was applied to the authority given to one person to transact business for another. The working partner had a commande from him who merely advanced capital. The term has acquired importance in political economy, because the law of France exempts the sleeping partners from responsibility beyond the amount they agree to be responsible for. On the other hand, by the law of the United Kingdom, every member of a partnership is liable for all its debts; limitation of liability being only obtainable by incorporation under the Companies Acts. Hence, in the discussions about the question, whether it would be prudent to relax this law, and permit persons to invest money in trading companies without undergoing this responsibility, such companies were called partnerships in commandite.' Proposals have from time to time been made in Britain to establish a system of limited partnerships independently of the Companies Acts. The Act 28 and 29 Vict. chap. 86, 5th July 1865, permits loans to trading firms in consideration of a