Collision, in mechanics. Whenever two bodies act on each other so as to change the direction of their relative motions, by means of any forces which preserve their activity undiminished at equal distances on every side, the relative velocities with which the bodies approach to or recede from each other will always be equal at equal distances Colluviarium, anciently a well or opening formed at intervals in the channel of an aqueduct for procuring a free current of air along its course, and to facilitate the operation of clearing away foul deposits left by the waters

Cologne earth is a native pigment, similar to the Vandyke brown in its uses and properties as a colour Colonnade, drange of columns, whether attached or insulated, and supporting an entablature

Colosseum, a name given to the theatre

of Vespasian, either from its magnitude or from its colossal statue of Nero; also the name of a fine building in the Regent's Park Colossus, a statue of gigantic dimensions, or very much beyond the proportions of nature

Colour. The term colour being used synonymously for pigment is the cause of much ambiguity, particu

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larly when speaking of colours as sensible or in the abstract; it would be well, therefore, if the term pigment were alone used to denote the material colours of the palette Colouring, in painting, the art of dis

posing the tints, so as to produce either an imitation of the natural colours of the objects represented, or force and brightness of effect Colouring, though a subject greatly inferior to many others which the painter must study, is yet of sufficient importance to employ a considerable share of his attention; and to excel in it, he must be well acquainted with that part of optics which has the nature of light and colours for its object. Light, however simple and uncompounded it may appear, is nevertheless made up, as it were, of several distinct substances; and the number and quantity of component parts have been happily discovered by the moderns Colours (symbolic), in antiquity, the middle ages, and modern times.

The history of symbolic colours is but little known. Colours had the same signification amongst all nations of the remotest antiquity: this conformity indicates a common origin, which extends to the earliest

state of humanity, and develops its highest energies in the religion of Persia: the dualism of light and darkness presents, in effect, the two types of colours which become the symbols of two principles, benevolence and malevolence. The ancients admitted but two primitive colours, white and black, whence all others are derived.

The language of colours, intimately connected with religion, passed into India, China, Egypt, Greece, and Rome, and re-appeared in the middle ages; the large windows of Gothic cathedrals found their explanation in the books of the Zends, the Vedas, and the paintings of the Egyptian temples.

Among the Egyptians, the prophets did not allow metal-founders or statuaries to represent the gods, lest they should deviate from the rules.

At Rome, the penalty of death was incurred by selling or being clothed in a purple stuff. At this day, in China, any one who wears or buys clothes with the prohibited design of the dragon or phoenix, is subjected to 300 stripes and three years' banishment.

Symbolism explains this severity of laws and customs: to each colour, to each pattern, appertained a religious or political idea; to change or to alter it was a crime of apostacy or of rebellion.

Archæologists have remarked that Indian and Egyptian paintings, and those of Greek origin, named Etruscan, are composed of plain tints of a brilliant colour, but without demi-tints; the pattern and the colour had a necessary signification, -it was essentially restrictive: perspective, chiaro-oscuro, and demitints, would have led to confusion.

Christianity, in recalling these forgotten significations, restores a new energy to the language of colours: the doctrine taught by Christ was not therefore new, since it borrowed the symbols of ancient

religions. The Son of God, in leading back mankind to the truth, came not to change, but to fulfil the law; this law was the worship of the true God.

The three languages of colours, divine, consecrated, and profane, classify, in Europe, the three estates of society, the clergy, the nobles, and the people.

The large glass windows of Christian churches, like the paintings of Egypt, have a double signification, the apparent and the hidden; the one is for the uninitiated, and the other applies itself to the mystic creeds. The theocratic era lasts to the renaissance; at this epoch, symbolic expressions are extinct; the divine language of colours is forgotten, painting became an art, and is no longer a science.

The aristocratic era commences; and symbolism, banished from the church, takes refuge at the court: disdained by painting, it is found again in heraldry. Modern painting still preserves its symbolism in church pictures: St. John wears a green robe, Christ and the Virgin are likewise draped in red and blue, and God in white.

Natural philosophy recognizes seven colours, which form the solar ray, decomposed by the prism; namely, violet, indigo, blue, green, yellow, orange, and red. Painting admits but five primitives,-the first and last of which are rejected by natural philosophy,-white, yellow, red, blue, and black. From the combination of these five colours every hue is produced.

According to symbolism, two principles produce all colours, light and darkness.

Light is represented by white, and darkness by black; but light does not exist but by fire, the symbol of which is red: setting out from this basis, symbolism admits two primitive colours, red and white. Black was considered as the negation of colours, and attributed to

the spirit of darkness; red is the symbol of divine love; white, the symbol of divine wisdom. From these two attributes of God, love and wisdom, the creation of the universe emanates.

Secondary colours represent different combinations of the two principles; yellow emanates from red and white; it is the symbol of revelation of the love and of the wisdom of God.

Blue emanates likewise from red and white; it indicates divine wisdom manifested by life, by the spirit or the breath of God (air, azure); it is the symbol of the spirit of truth.

Green is formed by the union of yellow and blue; it indicates the manifestation of love and wisdom in action; it was the symbol of charity, and of the regeneration of the soul by works.

Gold and yellow were, in Christian symbolism, the emblems of faith: St. Peter was represented by the illuminators and miniaturists of the middle ages with a goldenyellow robe, and the rod or the key in his hand.

Christianity restored truth to mankind, and re-instated symbolic language in its original purity. In the transfiguration, the countenance of our Lord became resplendent as the sun, and his vesture shone like the light. Such, in their highest energy, are the symbols of divine love and wisdom. The angel who rolled away the stone from the sepulchre reproduced them in an inferior order, his face shone like lightning, and his robe was white as snow. Finally, in the last degree, appeared the just, in robes washed white in the blood of the Lamb. The artists of the middle ages preserved their precious traditions, and gave to Jesus Christ, after the resurrection, white or red costume.

Columbaria, the holes left in walls for the insertion of pieces of tim

ber; so called from resembling the niches of a pigeon-house. The niches of a mausoleum, made to receive the cineral urns, were likewise termed columbaria Columbarium, a place of sepulture used for the ashes of the Romans, after the custom of burning the dead had been introduced among them

Columen, the term applied to the

upright timbers of a roof, corresponding to the modern kingposts

Column, in architecture, a member of a cylindrical form, consisting of a base, a shaft or body, and a capital. It differs from the pilaster, which is square on the plan. Columns should always stand perpendicularly

Columna (Latin), a pillar or column, used in architecture (as described in the orders), placed upright for support of buildings, principally wrought in stone, and made decorative in conformity to the order and style of architectural composition

Columns, in architecture, according to Vitruvius, of the three orders. The proportions of Corinthian columns are in every respect, excepting their capitals, similar to those of Ionic; although their form is more graceful and proportionably more delicate, by reason of the greater height of the capitals; for Ionic capitals are a third part only of the lower diameter of the columns, whereas the Corinthian capital is equal in height to an entire diameter. The peculiar character of the capitals, which admits of their being higher than those of Ionic columns by two-thirds of a diameter, gives beauty to them, by permitting an increase of the height without violating the laws of symmetry

Combustion, the operation of fire upon an inflammable substance, by which it smokes, flames, and is reduced to ashes

Combustion, Spontaneous. Few or no chemical combinations can take place without a disturbance in the equilibrium of caloric in the substances to be so combined; and when caloric is thereby evolved in sufficient extent and rapidity, and when one or all the bodies engaged may be freely combustible, ignition takes place. When this is unintentional, or is the result of ignorance or carelessness, it is convenient to call it spontaneous combustion.

Thus we frequently hear of hayricks, &c., on fire; occasionally, of carts loaded with quicklime being burned by the rain falling upon the lime. There are also somewhat apochryphal accounts of coal in coal-yards being destroyed in like manner. But the most important instance of this class, as far as regards the preservation of Government establishments, is the combustion that infallibly and rapidly ensues when greasy hemp, flax, or cotton, is allowed to remain loosely heaped together, in any quantity, in a confined unventilated space.

Full proof of this has been made by experiment in the dockyards; and there is much reason to attribute many fires in former days to carelessness in the rope-walks and hemp stores; in consequence of which, rigorous orders have been of late years issued as to the immediate disposal of loose oakum and hemp sweepings-all more or less greased or oiled. The very oil-rags used by engravers in cleaning plates, when heaped together to any amount, will be consumed in a few hours.

The combination in question seems to be between the oil and the oxygen of the atmosphere. Oil has always an affinity for oxygen; though, when the bulk of the former is considerable in proportion to the surface, the action is but feeble, and the results not ordinarily ap

:

preciable but in the case of admixture of such fibrous vegetable bodies as hemp, flax, or cotton with oily matters, where the ratio of surface to solidity is great, and when the conditions for accumulating heat are favourable, this accumulation soon produces ignition amongst such inflammable bodies as those just enumerated Come. Come home;' said of an anchor when it is broken from the ground, and drags. To come up' a rope or tackle, is to slack it off Commandry, a religious house be

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longing to a body of knights of the order of St. Bernard and St. Anthony

Commissure, the joint between two stones in masonry

Common pitch, an old term still applied by country workmen to a roof in which the length of the rafters is about three-fourths of the

entire span

Common sewer of Rome: it was near the Senatorian bridge, and was 16 feet in diameter Communication valves, the valves in a steam-pipe which connects two boilers to an engine, for cutting off the communication between either boiler and the engine Communion table, a piece of church

furniture usually placed near the wall of the east end of the chancel, and enclosed by rails, within which the clergyman stands to administer the Sacrament Companion, a wooden covering over the staircase to a ship's cabin Compartition, the division or distri

bution of the ground-plan of an edifice into its various apartments Compartment of the streets within a city. According to Palladio, regard must be always had to the temperature of the air, and also to the region of heaven, or the climate under which the place is situated; because where the air is cold or temperate, there the streets ought to be made large and noble, since thereby the city will become