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During their short stay in this country, they are to be seen, not unfrequently, in Kent, in flocks of about fifteen or twenty, and commit no small depredations on the pea fields of that county, peas being their most favourite food. They build generally in the woods, and on the highest trees. The sounds of the male are particularly soft and impressive, and his assiduity to please the companion of his joys and cares has induced the poets of every age to exhibit him as a model of pure, constant, and delicate attachment. See Aves, Plate IV. fig. 7.

C. migratoria, or the American migratory pigeon. These birds pass the summer in the northern parts of North America, and on the approach of winter move towards the southern. They build in trees, and feed principally upon acorns, and mast of every description. They are also extremely fond of rice and corn. They pass in their periodical migrations in flocks, stated to extend in length two miles, and a quarter of a mile in width; Occasionally alighting in the course of their journey, and covering the foliage of considerable woods. During what is called their flight time, the common people of the country easily knock them from their roosts, and find them a very nourish. ing and pleasant, as well as cheap article of food. In Louisiana, it is a common entertainment in an evening, in which ladies frequently participate, to enter the woods frequented by these birds, and burn a small quantity of sulphur under the trees on which they are lodged. Stupified by this application, they almost immediately quit their hold, and drop lifeless to the ground, whence they are picked up in quantities.

C. œnas inhabits old turrets, and rocky banks of Europe and Siberia, fig. 2. COLUMBATES. 7 See COLUMBIUM. COLUMBIC acid. S

COLUMBIUM, in mineralogy and chemistry. Mr. Hatchet, in examining some minerals in the British Museum, observed one which attracted his attention, from its resemblance to chromate of iron. On analysing it, he found it to be composed of a metallic acid, united with oxide of iron; and this acid, by farther experiments, was found to differ in its properties from every other. Mr. Hatchet did not succeed in reducing it to the metallic state. To the metal, however, which he supposed to be its basis, he gave the name of Columbium, as the ore affording it was the produce of America. The mineral which afforded this metallic VOL. III.

acid is of a dark brownish grey colour; its lustre is vitreous, inclining to metallic: its fracture imperfectly lamellated: it is moderately hard and very brittle: its particles are not attracted by the magnet: its specific gravity is 5.9. From this mineral Mr. Hatchet extracted the

peculiar matter which may be named columbic acid. The columbic acid is of a pure white colour, and not extremely heavy; it has scarcely any taste, nor does it appear to be soluble in boiling water, but, when placed on litmus paper, mixed with distilled water, soon renders the paper red.

From the acid solutions of columbic acid, the alkalies throw it down in the form of a white flocculent precipitate. Prussiate of potash changes the colour to an olive-green, and a precipitate of the same colour is gradually formed. Tincture of galls produces a deep orange-coloured precipitate, especially when there is not too great an excess of acid present. Zinc, immersed in the solution, gives rise to a white precipitate. The fixed alkalies combine readily, both in the humid and in the dry way, with_columbic_acid, forming with it salts called columbates. When fused with it, a compound is formed, which is soluble in water; and if the alkali be in the state of carbonate, the carbonic acid is disengaged during the fusion with effervescence. When a solution of potash is boiled on it, a quantity is dissolved; the solution, which has a considerable excess of alkali, affords, by gentle evaporation, a white salt in shining scales, having a disagreeable acrid flavour, not soluble very readily in cold water, but, when dissolved, the solution is permanent. Nitric acid added to it precipitates the columbic acid. Prussiate of potash and tincture of galls produced no change; but when with either of them a few drops of muriatic acid were added, precipitates, similar to those produced by these re-agents in the acid solutions, appeared an olive green with the one, and an orange-coloured precipitate with the other. Hydro-sulphuret of ammonia produced a reddish brown precipi

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tincture of galls, in not combining with ammonia, and in being insoluble, and unalterable with regard to colour, by nitric acid.

COLUMELLA, in botany, a genus of the Syngenesia Superflua class and order; receptacle naked, cellular; seeds crowned with a toothed margin; calyx cylindrical, imbricate; florets of the ray undivided. One species, found at the Cape.

COLUMN, a round pillar, made to support and adorn a building, and composed of a base, a shaft, and a capital.

Columns are different in the different orders of architecture, and may be considered with regard to their matter, construction, form, disposition, and use. See ARCHITECTURE,

COLUMNEA, in botany, a genus of the Didynamia Angiospermia class and order. Natural order of Personatæ. Scrophulariæ, Jussieu. Essential character: calyx five-parted; corolla ringent; upper-lip three-parted; the middle part vaulted, emarginate; gibbous above at the base; anthers connected; capsule two-celled; seeds nestling. There are six species, all natives of hot countries, and most of them of the West Indies.

COLUMNIFERE, in botany, the name of the thirty-seventh order in Linnæus's "Fragments of a Natural Method," consisting of plants whose stamina and pistil have the appearance of a pillar in the centre of a flower: an instance of this order is the genus BfxA, which see.

COLURES, in astronomy and geography, two great circles, supposed to intersect each other at right angles in the poles of the world, and to pass through the solstitial and equinoctial points of the ecliptic. That which passes through the two equinoctial points is called the equinoctial colure, and determines the equinoxes; and the other which passes through the poles of the ecliptic is called the solstitial colure, because it determines the solstices.

COLUTEA, in botany, a genus of the Diadelphia Decandria class and order. Natural order of Papilionacea or Leguminosæ. Essential character: calyx fivecleft; legume inflated, gaping on the upper suture at the base. There are nine species. Most of the Coluteas are shrubs, with pinnate leaves, and stipules distinct from the petiole; peduncles sometimes two-flowered, but more frequently manyflowered in spikes, both axillary and ter minating. They are easily distinguished

by their membranaceous, inflated pod; natives of hot climates.

COLYMBUS, the diver, in natural history, a genus of birds of the order Anseres. Generic character: bill toothless, subulate, straight, and pointed throat toothed; nostrils linear; legs fettered. The guillemot and the diver are included by Gmelin under one genus, while Latham considers each as furnishing a genus by itself. We shall adopt the system of the former, and notice, in what follows, the most important of these two classes, under one head.

C. troile, or foolish guillemot. These birds are, in summer, surprisingly abundant on the coasts of England, and furnish to the sportsman an invaluable supply of experience in the art of shooting flying. Whatever numbers may be destroyed, the rest only quit their stand to take a circular flight, which brings them back to the spot whence the gun alarmed them, and which the death of their companions cannot induce them finally to leave. Their flesh is eaten by the Kamschatkans, though extremely ill flavoured, and their skins valued by those people as a highly ornamental dress. The eggs are said to be extremely delicate, and it is remarkable that no two are spotted or streaked alike.

C. glacialis, or the Northern diver, is the largest of the genus, and weighs so much as sixteen pounds, measuring three feet six inches in length. This is found in various places in the North of Europe, but scarcely ever seen so far south as England, unless in winters extremely rigorous. It is rarely seen on land, being almost perpetually on the ocean, where it dives with extreme vigour in pursuit of various fishes, and with such dexterity as rarely fails of success. It can fly with rapidity, and to a great distance. In Iceland it is often found, and, while breeding, fre quents the lakes and rivers of that island. The inhabitants of the banks of the Oby prepare the skin of this bird without injuring the feathers, and ren der it convertible into compact, durable, and ornamental parts of dress, as caps, or even mantles, which are proofs against moisture, and afford extraordinary

warmth.

C. immer, or the imber, resembles the last in habits and manners. It is fouud in the lakes of Canada, and in those of Switzerland, as well as in almost all the northern parts of Europe. It will swim under water to the distance of a hun

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COMA, or COMA-VIGIL, a preternatural propensity to sleep, when nevertheless the patient does not sleep, or, if he does, awakes immediately without any relief. See MEDICINE.

Coma, in botany, a collection of floral leaves, which, in the crown imperial, lavender, sage, cow-wheat, and some other plants, terminate the flower-stem, and form an appearance like a tuft of hair.

COMA Berenices, Berenice's hair, in astronomy, a constellation of the Northern hemisphere, composed of stars near the Lion's tail. See ASTRONOMY.

COMARUM, in botany, a genus of the Icosandria Polygamia class and order. Natural order of Senticosa. Rosacea, Jussieu. Essential character: calyx tencleft; petals five, smaller than the calyx; receptacle of the seeds ovate, spongy, permanent. There is but one species; viz. C. palustre, marsh-cinquefoil, a native of most parts of Europe, in boggyground.

COMB, an instrument made of horn, ivory, tortoise-shell, box, or holly-wood, &c. and useful for separating and adjusting the hair, &c.

COMB-making. Combs are not only made for the purpose of cleansing the hair, but for ornament: they are sometimes set with brilliant stones, pearls, and even diamonds; some again are studded with cut steel: these are of different shapes, and are used to fasten up the hair when ladies dress without caps. Combs may, of course, be had of all prices, from the value of a few pence to almost any sum. They are generally made of the horns of bullocks or of elephants, and sea-horse's teeth, and some are made of tortoise-shell and ivory, others of box or holly-wood. The horns of bullocks are thus prepared for this manufactory: the tips are sawn off; they are then held in the flame of a wood fire; this is called roasting, by which they become nearly as soft as leather. While in that state they are slit open on one side, and pressed in a machine between two iron plates; they are then plunged into a trough of water, from which they come out hard and flat; they are then sawn into lengths, according to the size wanted.

To cut the teeth, each piece is fixed into a tool called a claw. The maker sits on a triangular sort of a stool to his work, and under him is placed the claw that holds the horn, ivory, &c. that is to be formed into a comb. The teeth are cut with a fine saw, or rather a pair of saws, and they are finished with a file. A coarser file, called a rasp, is used to reduce the horn, &c. to a proper thickness; and when they are completely made, they are polished with charcoal and water, and receive their last finish with powder of rotten stone. The process used for making ivory combs is nearly the same as that already described, except that the ivory is first sawed into thin slices. The best ivory comes from the island of Ceylon, and Achen, in the East Indies; as it possesses the property of never turning yellow, it is consequently much dearer than any other kind.

Tortoise-shell combs are much esteemed; and there are methods of staining horn, so as to imitate it, of which the following is one; the horn to be dyed is first to be pressed into a flat form, and then done over with a paste, made of two parts of quick-lime and one of litharge, brought into a proper consistence with soap-ley. This paste must be put over all the parts of the horn, except such as are proper to be left transparent, to give it a nearer resemblance to tortoise-shell. The horn must remain in this state till the paste be quite dry, when it is to be brushed off. It requires taste and judgment, so to dispose the paste, as to form a variety of transparent parts, of different magnitudes and figures, to look like nature. Some parts should also be semitransparent, which may be effected by mixing whiting with a part of the paste. By this means spots of a reddish brown will be produced, so as greatly to increase the beauty of the work. Horn thus dyed is manufactured into combs, and these are frequently sold for real tortoise-shell.

COMBAT, in law, or single combat, denotes a form of trial between two champions of some doubtful cause or quarrel, by the sword or batoons. This form of proceeding was anciently very frequent, particularly among the barbarous nations in their original settlements; and obtained, not only in criminal, but also in civil causes; being built on a presumption, that God would never grant the victory but to him who had the best right. It was originally permitted, in order to determine points respecting the reputation

of individuals, but afterwards became much more extensive. The accuser first swore to the truth of his accusation; the accused gave him the lie: upon which each threw down a gage, or pledge of battle, and the parties were committed prisoners to the day of combat. See CHAMPION.

COMBINATION, in mathematics, is the variation or alteration of any number of quantities, letters, sounds, or the like, in all the different manners possible. It is shewn, in the memoirs of the French Academy, that two square pieces, each divided diagonally into two colours, may be combined 64 different ways, so as to

form so many different kinds of chequer work; which appears surprising enough, when one considers that two letters or figures can only be combined twice. See CHANGES.

COMBINATION, doctrine of Prob. 1. Any number of quantities being given, together with the number in each combination, to find the number of combinations. One quantity admits of no combination: two, a and b, only of one combination; of three quantities, a b c, there are three combinations, viz. a b, a c, bc; of four quantities, there are six combinations, viz, a b, a c, a d, bc, bd, cd; of five quantities, there are ten combinations, viz. a b, a c, bc, a d, b d, c d, a e, be, ce, de. Hence it appears that the numbers of combinations proceed as 1, 3, 6, 10; that is, they are triangular numbers, whose sides differ by unity from the number of given quantities. If this then be supposed q, the side of the number of combinations will be q 1, and so the q 1, q +0. number of combinations

See TRIANGULAR NUMBERS.

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1

If three quantities are to be combined, and the number in each combination be three, there will be only one combina tion, a be; if a fourth be added, four combinations will be found, a b c, a b d, bcd, a cd; if a fifth be added, the combinations will be ten, viz. a b c, ab d, b cd, a cd, a be, bde, bce, a ce, a de; if a sixth, the combinations will be twenty, &c. The numbers, therefore, of combinations proceed as 1, 4, 10, 20, &c. that is, they are the first pyramidal triangular numbers, whose side differs by two units from the number of given quantities. Hence, if the number of given quantities be q, the side will be q 2, and so the 2, q-1, number of combinations

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99-1 1 2 which is the sum of 3 4 the unciæ of the binomial raised to the power q, and abridged of the exponent of the power increased by unity q +1. Wherefore, since these unciæ come out 1+ 1, by being raised to the power g and since 1+1 is equal to 2, 2q-q-1 will be the number of all the possible combinations. For example, if the num ber of quantities be 5, the number of possible combinations will be 25—6—32— 6=26.

Prob. 2. Any number of quantities being given, to find the number of all these changes which these quantities, combined

23

1391724288887252999425128493402200. In so many various methods may the 24 letters of the alphabet be varied and combined among themselves.

in all the manners possible, can under. (2435—24) ÷ (24 — 1) = 32009658644go. Let there be two quantities a and b, 406818986777955348250600 divided by their variations will be two; consequently, as each of them may be combined with itself, to these there must be added two variations more. Therefore the number of the whole will be 2 + 2 = 4. If there were three quantities, and the exponent of the variation 2, the combinations will be 3, and the changes 3; to wit, a b, a c, bc, and ba, ca, cb; to which if we add the three combinations of each quantity with itself a a, b b, c c, we shall have the number of changes 3+3+3

: 9.

In like manner, it is evident, if the given quantities were 4, and the exponent 2, that the number of combinations will be 6, and the number of changes like wise 6, and the number of combinations of each quantity with itself 4; and therefore the number of changes 16; if with the same exponent the given quantities were 5, the number of changes would be 25; and in general, if the number of the quantities were n, the number of changes would be n2.

bba,

Suppose the quantities 3, and the exponent of variation 3, the number of changes is found 27 = 33, viz. a a a, a ab, aba, baa, a ac, a ca, ca a, a bb, bab, ab c, b ac, bca, ac b, c ab, c ba, a cc, ca c, c c a, b b b, bbc, c b b, b c b, bc c, с b c, c c b, c c c. In like manner it will appear, if the quantities were 4, and the exponent 3, that the number of changes would be 64 43; and in general, if the number of quantities was = n, and the exponent 3, the number of changes would be n3.

By proceeding in this manner it will be found, if the number of quantities be n, and the exponent n, that the number of changes would be nn. Where fore, if all the antecedents be added, where the exponent is less, the number of all the possible changes will be found nn + nn−i + nn~2 + nn−3 + nn−4, &c. till the number subtracted from n leaves 1, because the beginning is from single quantities taken once.

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Since, then, the number of all possible changes is in a geometrical progression, the first or smallest term of which is n, the largest nn, and the denominator n1 it will be equal (nntı →n) ÷ (n 1). Suppose n = 4, the number of all possible variations will be (45-4)-÷(1—4)= 1020 =340.

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Suppose again n 24, the number of all the possible variations will be

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COMBINATION, in chemistry, is the intimate union of two bodies, by chemical attraction, into one substance, so that neither of them can be recognized, nor can they be separated from each other by any mechanical force. Of this principle are the following instances. Salt will unite with water, from which it cannot be separated again but by chemical agency. Sulphur and lime may by heat be united, and form a compound, the properties of which are totally dissimilar to those of either the substances used. both cases an affinity has been exerted between the substances, and they have combined. Combination is to be distinguished from mixture, in which dissimilar particles are blended together, without being united by attraction, in which no new qualities are acquired, in which the difference of parts is easily discovered, and these parts are capable of being separated by mechanical means. It is distinguished from aggregation, which is merely the union of particles of the same kind of matter, forming an aggregate, uniform in composition, but possessing all the properties of the particles of which it is composed.

COMBINATION, in military science. One ought to regard combination as forming a part of military science. A general, who has an enterprize in contemplation, should, before he risks the execution of it, combine well in his mind all the ideas that can lead to its success; and he ought not always to rely on his own solution of the case. But when his ideas on the subject are pretty well fixed, he should lay them before the general officers, who are under his orders or command, for their opinion and concur

rence.

COMBINATION, in law. Combinations to do unlawful acts are punishable before the unlawful acts are executed; this is to prevent the consequences of combination and conspiracies, &c.

COMBRETUM, in botany, a genus of the Octandria Monogynia class and order. Natural order of Calycanthemæ. Onagræ, Jussieu. Essential character: calyx four or five toothed, bell-shaped, superior; corolla four or five-petalled, inserted into the calyx; stamina very long; seed one, four or five-angled, the angles membranaceous. There are four

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