casioned by the progressive motion of light and the earth's annual motion in its orbit Aberration, in optics, the deviation or dispersion of the rays of light when reflected by a lens, by which they are prevented from meeting or uniting in the same point, called the geometrical focus; but spread over a small span, they produce a confusion of images Ablactation, in gardening, the method of grafting Ablaqueation, the opening of the ground around the roots of trees, for the admission of the air Aboard, a nautical term, the inside of a ship, or to go on board About-ship, the situation of a ship after she has tacked About-sledge, the largest hammer employed by smiths; it is slung round near the extremity of the handle, and generally used by under workmen, called hammer-men Abrasion, the effect produced by at trition or rubbing Abreast, as when two ships have or joint between two stones to be filled up with mortar or cement Abscissa, a geometrical term for a segment cut off from the straight line by an ordinate to a curve Absorbents, in chemistry, those earthy substances capable of uniting, by capillary attraction, a large proportion of water: such are magnesia, lime, and clay, when dry and porous Absorption, in chemistry, takes place when, by the combination of gases with other substances, a very considerable diminution of volume is experienced: it differs from condensation Abstract (To), a term used by artificers and surveyors in arranging and apportioning their work, to explain and price it Abstract mathematics, otherwise denominated pure mathematics, that ABU branch of the science which treats of simple properties, magnitude, figure, or quantity, absolutely and generally considered Absurd, a term used in demonstrating converse propositions Abundant number, a number whose aliquot parts, added together, make a sum which is greater than the number itself Abuses. "Architecture," says Palladio, "being an imitatrix of Nature, delights in that which is most consonant with her prototype." Ancient edifices were built with wood, trees forming the columns; and when architects began to build with stone, they made the columns to imitate the trunks of trees, tapering from their bases. Being thus originally of wood, and therefore liable to split when much loaded, they bound them with rings at top and bottom. Thus the bases and capitals in the different orders seem originally derived from these bandages, though they are now become essential ornaments. Thus also in entablatures, the triglyphs, modillions, and dentils represent the ends of those beams and timbers which are employed for the support of the floors and roofs. If, therefore, all these conditions be duly considered, those practices in building are highly to be reprobated which are in opposition to that analogy which should exist between the original and its imitation, or which depart from Nature and the simplicity observable in all her works. Consoles or cartouches, which are of a scroll-like form, should never be employed for the apparent support of great weights, in place of columns or pilasters; nor should they ever project from, or spring out of, cornices. Pediments and frontispieces over doors and windows, or elsewhere, should on no account be broken or disconnected in the middle; for the intention of these is to shelter the parts below from the rain, and this result is completely obviated by such a practice. The projecture of cornices, though for the purpose of sheltering buildings, should not be more than in due proportion to their height, whether or not accompanied by columns; for if too heavy, they seem to threaten with danger those who are under them; and if too small in projection, they do not properly perform their office. Again, those columns which are feigned to be composed of several pieces, by being jointed together with rings, should be carefully avoided, because the more solid and strong the columns appear, the better they seem to answer the purpose for which they were erected, which is securely to receive the superincumbent loading. There are many other abuses which the authority of great masters may sanction, but not justify; and such will readily occur to the student, and themselves point out that they ought to be avoided Abutment, the solid part of a pier from which the arch springs Abutments, the extremities of a bridge, by which it joins upon the banks or sides of a river, &c. : in carpentry and joinery, the junctions or meetings of two pieces of timber, of which the fibres of the one run perpendicular to the joint, and those of the other parallel to it Abuttals, the buttings or boundaries of land Abyss, in heraldry, the centre of an escutcheon Acacio, a heavy, durable wood of the red mahogany character, but darker and plainer; it is highly esteemed in ship-building Academia, in antiquity, a villa or pleasure-house in one of the suburbs of Athens, where Plato and other philosophers assembled Academician, a member of a society or academy instituted for the cultivation of the arts and sciences Acanthus, the plant branca ursina, in English bear's breech, the leaves of which are imitated in decorating the Corinthian and Composite capitals of columns Accelerated motion, a force acting incessantly upon a body; called also a constant or uniformly accelerating force when the velocity increases equally in equal times: the force of gravity near the earth's surface is of this kind; it generates a velocity of 32 feet in each second of time; that is, a body, after falling one second, acquires a velocity of 324 feet; after falling two seconds, it will acquire a velocity of 2 × 321 feet; after three seconds, a velocity of 3 x 32 feet, and so on Accelerating force, in physics, the force which accelerates the motion or velocity of bodies; it is equal to, or expressed by, the quotient arising from the motion or absolute force, divided by the mass or the weight of the body moved Accelerative or retardative force, is commonly understood to be that which affects the velocity only, or that by which the velocity is accelerated or retarded; it is equal or proportional to the motive force directly, and to the mass or body moved inversely Accesses, approaches or passages of communication between the various apartments of a building, as corridors Accessible, in surveying, a place which admits of having a distance or length of ground measured from it; or such a height or depth as can be measured by the application of a proper instrument Accessories, or accompaniments, in painting, secondary objects to the principal one in a picture, introduced as explanatory and illustrative of the scene: sometimes they are considered as solely contributing to the general effect and harmony of the piece Accidental point, in perspective, the point in which a right line drawn from the eye, parallel to another Acclivity, the slope or steepness of a line or plane inclined to the horizon, taken upwards; in contradistinction to declivity, which is taken downwards Accouplement, in carpentry, a tie or brace, or the entire work when framed Accretion, in physics, the growth or increase of an organized body Accroché, in heraldry, denotes the hanging of one thing upon another Accubitus, a room annexed to large churches, in which the clergy occasionally reposed Aceric acid, in chemistry, an acid formed from the juice of the maple tree Acerra, in antiquity, an altar erected, among the Romans, near the bed of a person deceased, on which his friends daily offered incense until his burial Acetate of lead,-sugar of lead,-a compound of acetic acid and lead Acetate of potash, a compound of acetic acid and potash, produced by dissolving carbonate of potash in distilled vinegar Acetates, crystallizable salts, formed by the combination of any base with acetic acid, named also radical or pure vinegar Achromatic, a term expressing absence of colour: in optics, applied to telescopes invented to remedy aberrations and colours Acids, in chemistry, are sour to the taste, and convert vegetable blues to a red colour; they combine with alkalies, earths, and metallic oxides, and form, with them, the wellknown compounds named salts Acinose, a term applied to iron ore found in masses, and of several colours A-cock-bill, in navigation, the situ ation of the yards when they are topped up at an angle with the deck; the situation of an anchor when it hangs to the cat-head by the ring only ACT Acolyte, in the ancient church, a person who trimmed the lamps, prepared for the sacrament, &c. Acoustics, the doctrine or theory of sounds, consisting of diacoustics, or direct sounds, and catacoustics, or reflecting sounds Acre, a measure of land, containing, by the ordinance for measuring land in the time of Edward I., 160 perches or square poles of land; and as the statute length of a pole is 5 yards or 16 feet, the acre contains 4840 square yards, or 43560 square feet. The chain with which land is now commonly measured, invented by Gunter, is 4 poles, or 22 yards, in length; and the acre is therefore just 10 square chains; and as a mile contains 1760 yards, or 80 chains, in length, the square mile is equal to 640 acres. The acre, in surveying, is divided into 4 roods, and the rood into 4 perches Acrolithes, in sculpture, statues, the extremities of which are formed of stone Acropolis, a building strictly applicable to a Greek city, and usually erected upon a hill, rock, or some natural elevation, and devoted to a magnificent temple; also a tower, castle, or citadel Acrostolion, in ancient naval archi tecture, an ornament of the prow or forecastle of a ship, chiefly of war, most frequently circular or spiral Acroteria, small pedestals at the angles and vertex of a pediment: the gate of the Agora at Athens is the only instance in which they appear in Grecian buildings Actinometer: Sir John Herschel, at the third meeting of the British Association, submitted an instrument for measuring at any instant the direct heating power of the solar ray it affords a dynamical measure of the solar radiation, by receiving a quantity of heat per second, or any short space of time, on a surface exposed to the sun. In making observations with this instrument, it should be freely exposed in the shade for one minute, and the variation read; afterwards expose it for the same time to the solar action, and again note it; and lastly, repeat the experiment in the shade: the mean of the two variations in the shade being subducted from the variation in the sun, the excess gives the dilatation per minute due to the sun's rays; the quantity subducted being the effect of the other causes at the time Actus, a Roman measure of length, equal to 120 Roman feet Acute angle, in geometry, less than a right angle, and measured by less than 90°, or a quadrant of a circle Acute-angled cone, that in which the opposite sides make an acute at the vertex, or whose axis, in a right. cone, makes less than half a right angle with the side Acute-angled section of a cone, an el lipsis made by a plane cutting both sides of an acute-angled cone Acute-angled triangle, that in which the three angles are all acute Adamant, a very hard stone, used by the ancients for cutting and polishing other hard stones and glass Adeling, a title of honour given to the children of princes among the Anglo-Saxons Adhesion, the force with which differ ent bodies remain attached to each other when brought into contact Adit, the passage or approach to a house; applied also to the horizontal shaft of a mine, driven for the purposes of ventilating, watering, or draining Adit level, in mining, a horizontal excavation through which the water is drawn by the engine Adjacent angle, in geometry, an angle immediately contiguous to another, so that one side is common to both Adjutage (Ajutage), or jet d'eau, a tube fitted to the aperture of a vessel through which water is to be played Adonia, a festival celebrated in ho nour of Aphrodite and Adonis in most of the Grecian cities Adrift, the condition of a vessel broken from her moorings Adumbration, in heraldry, a figure painted of the same colour as the ground of the field, but darker Adytum, the most sacred place in the heathen temples; the Holy of Holies; in Christian architecture, the chancel or altar-end of a church Adze, an edged tool used to chip surfaces in a horizontal direction; the are being employed to chop materials in vertical positions Ecclesiolo, in Domesday Book, a cha pel subordinate to the mother church Edes, an inferior kind of temple; in Christian architecture, a chapel ; also sometimes applied to a house Edicula, a small chapel, house, or building of any kind; not unfrequently applied to the niches of tabernacles in a wall which held statues of the lares or penates Eyricanes, a name given to rams' heads when sculptured on friezes, altars, &c. Eolipile, in hydraulics, an instrument consisting of a hollow metallic ball with a slender neck or pipe proceeding from it, which, being filled with water, produces a violent blast of wind Eolus, a small portable machine for refreshing and changing the air of apartments Erarium, a treasury among the Ro mans; the place where public money was deposited Aerial perspective, the relative apparent recession of objects from the foreground, owing to the quantity of air interposed between them and the spectator Aërology, the doctrine or science of the air Aërometer, an instrument contrived to ascertain the mean bulk of gases Aerometry, the science of measuring the air, its powers and properties Aeronautics, the art of sailing or floating in the air Aerostatics, the doctrine of the weight, pressure, and balance of the air and atmosphere Ærugo, rust, more especially that of copper; verdigris Esthetics, the power of perception by means of the senses: the word implies the perception and the study of those qualities which constitute the beautiful and artistic, and form the finer essence of all productions of fine art. It carries with it, therefore, a more exact and philosophic meaning than the word 'taste.' In its adjective form, in which it more frequently occurs, it is particularly useful, as no adequate epithet can be substituted for it. Thus we speak of theæsthetic sense,' of' æsthetic feeling,' or 'study,' or 'principles,' &c.; but we cannot correctly say the tasteful sense,' or 'tasteful study' Aëtoma, a pediment, or the tympanum of a pediment Affinity, in chemistry, the power by which the ultimate particles of matter are made to unite, and kept united Afflux, a flow of electric matter to a globe and conductor, in opposition to efflux, from them After, in ship-building, implies a connexion, as belonging to the afterbody, after-timber, &c. Agalma, a sculptural ornament or image Ager, a Roman acre of land Agger, a heap or mound of any kind, formed of stone, wood, or earth Agglutination, the cohesion of bodies Aggregation, in chemistry, the collec tion of bodies, solid, fluid, or gaseous Agora, a place of public assembly in a Greek city for the transaction of all public business; a marketplace Aguilla, an obelisk, or the spire of a church tower A-hull, the condition of a vessel when she has all her sails furled, and her helm lashed a-lee Air-casing, the sheet-iron casing which surrounds the base of the AIR chimney of a steam vessel, to prevent too great a transmission of heat to the deck Air-drains, cavities between the external walls of a building, protected by a wall towards the earth, which is thus prevented from causing dampness Air-escape, a contrivance for letting off the air from water-pipes Air-holes, those made for admitting air to ventilate apartments Air-machine, in mining, the apparatus used for forcing purer air into or withdrawing foul air from parts badly ventilated Air-pipes, in mining, tubes or pipes of iron or wood, for ventilating under ground, or for the conveyance of fresh air into levels having but one communication with the atmosphere, and no current of air: also used for clearing foul air from the holds of ships or other close places Air-pump, a pneumatic instrument, by means of which the air is exhausted out of the proper vessels : its effects are produced by the elasticity of the air; and as at each stroke of the pump only a part of the remaining air is withdrawn, an absolute vacuum cannot be obtained, although so near an approximation to it may be had as to remove the general effects of the atmosphere. The proportion of the air-pump, as given by Watt, is usually about two-thirds of the diameter of the cylinder, when the length of the stroke of the airbucket is half the length of the stroke of the steam piston. The area of the passages between the condenser and the air-pump should never be less than one-fourth of the area of the air-pump. The apertures through the air-bucket should have the same proportion; and, if convenient, the discharging flap or valve should be made larger. The capacity of the condenser should at least be equal to that of the air-pump; but, when conveni |