ACCENTOR which it is indeed difficult to form any accurate conception. The history of the employment of accentual marks in writing the Greek They are language is extremely obscure. found in manuscripts of considerable antiquity. In our pronunciation of Greek, they are wholly neglected. But the modern Greeks pronounce their language, in general, laying the stress on the accented syllables, and neThe mark of the glecting the quantity. acute accent is '; of the grave; of the circumflex, which is a compound of the other two, or But every syllable which has no accentual mark is said to have the grave accent; the grave being only marked on final syllables of words which have no acute accent on any syllable. These three accentual marks are also employed in the French language; but in it they are only employed, for convenience, to mark a difference in the pronunciation, not in the accent; the modifications of the vowel sounds not being all of them expressed by distinct letters. measure. ACCENT. In Music, a certain stress or forced expression laid on certain parts of a bar, or The first note of a bar has the strongest accent, but subordinate or weaker accents are also laid on the first notes of any For example, subordinate divisions of the bar. in a bar of eight quavers, the first has a strong accent, the third, fifth, and seventh weaker accents. In a bar of nine quavers, the first has a strong accent, the fourth and seventh weaker Sometimes an abnormal accent is laid on what would otherwise be a weak note. This is called emphasis, and its skilful use is a great beauty in composition. ones. Accentor. A genus of seed and insect-eating passerine birds, of which the hedge-chanter, or, as it is commonly called, the hedge-sparrow (Accentor modularis), is a well-known example. Acceptance. [BILL OF EXCHANGE.] Acceptor (Lat.). [BILL OF EXCHANGE.] Accessary or Accessory (Fr. accessoire). In English Law, an accessary to an offence is one who is not the chief actor, or present at its performance, but is concerned An therein, either before or after the fact. accessary before the fact is one who, being absent at the time of the crime committed, doth yet procure, counsel, or command another to commit a crime.' An accessary after the fact is one who, knowing that a felony has been committed by another, receives, relieves, The law of comforts, or assists the felon. accessaries and abettors is now regulated by 24 & 25 Vict. c. 94. [LAW, CRIMINAL.] ACCESSARY. In Painting and the Fine Arts, is a term which extends to everything introduced into a work that is not absolutely necessary, or only illustrative. In an historical picture, for instance, the figures which are in action are the principal objects; by them the story is told; all the rest are accessories. Especial care is to be taken that they be so selected and disposed as not to interfere with 13 ACCIDENTAL POINT the principal group; hence the ancient painters Accidens, per accidens (Lat.). A term Accident. In Logic, one of the predicables: In Heraldry, an additional Accidental. mark in a coat of arms which may be either retained or omitted without altering its character. Accidental Colours. Colours depending on the hypersensibility of the retina of the eye for complementary colours. If we look for a short time steadily with one eye upon any bright-coloured spot, as a wafer on a sheet of paper, and immediately after turn the same eye to another part of the paper, a similar spot will be seen, but of a different colour. If the wafer be red, the imaginary spot will be green; if blue, it will be changed into yellow; the colour thus appearing being always what is termed the complementary colour of that on which the eye was fixed. Accidental Point. In Perspective, the point in which a straight line drawn from the eye, parallel to another straight line, cuts the perspective plane. It is the point in which the representations of all straight lines parallel to the original straight line concur when produced. It is called the accidental point, to ACCIDENTALS distinguish it from the principal point, or point of view. Accidentals. In Music, are those flats and sharps which are prefixed to the notes in the course of a movement, and are not indicated by the signature at the commencement. ACCIDENTALS. In Painting, are those fortuitous or chance effects, occurring from luminous rays falling on certain objects, by which they are brought into stronger light than they otherwise would be, and their shadows are consequently of greater intensity. This sort of effect is to be seen in almost every picture by Rembrandt, who used them to a very great extent. There are some fine instances of accidentals in Raphael's Transfiguration, and particularly in the celebrated picture, the Notte of Correggio, in which the light emanates from the infant Christ. With these effects may be classed such accidental lights as those from a forge or a candle, or some such object, of which the use is extremely important to the painter of still life. Accipitres (Lat. accipiter, a hawk). The name of the Linnæan order including the birds of prey. Acclimatise (Lat. ad, to, and clima, a climate). The supposed art of cultivating exotic plants so as to inure them to a climate different from that which is natural to them. An acclimatised plant or animal is said to differ from a naturalised one, in always requiring the assistance of art for its continuance in the adopted climate; the naturalised plant or animal continuing its kind without any care from man. It is, however, to be observed that what passes under these terms is frequently nothing more than the fortunate discovery that some plant or animal, which had hitherto been found in a warm climate, would thrive equally well in a cold one. It is doubtful whether any case of true acclimatisation is known among plants. Accolade (Fr). The slight blow given to the neck or shoulder, on dubbing a knight. Accompaniment. In Music, the instrumental part of a composition which moves with the voice, to which it is to be kept subordinate. Also, the parts which in a concerted piece move with a particular instrument, whose powers it is the object of the composition to exhibit. ACCOMPANIMENT. In Painting, any object accessary to the principal subject, and serving to ornament or illustrate it. Accord. [CONCORD.] Accordion (Ital. accordare, to harmonise). In Music, a free reed portable instrument, something like the concertina, but inferior. Account Stated. In Pleading (English Law), a 'count' in an action whereby the plaintiff alleges that the defendant is indebted to him in a certain amount on a statement of accounts between them. Accountant-General. The principal or responsible accountant in the offices of Excise and Customs, India House, Bank of England, &c. The accountant-general of Chancery is an ACEPHALOCYST officer appointed by act of parliament to receive all the money lodged in court. He keeps his account with the Bank of England, which is responsible for all the sums lodged there by him. Accrescent (Lat. accrescens, part. of accresc, I grow). In Botany, when an organ is persistent and increasing in size; as the calyx of the winter-cherry, which becomes enlarged after the plant has flowered. Accrescimento (Ital.) In Music, the increase, by one half of its original duration, which a note gains by having a dot appended to the right of it. Accumbent (Lat. accumbens, part. of accumbere, to lie down). A botanical term used in cases where one part of an organ is applied to another by its edge; in contradistinction to incumbent, where one part is applied to another by its back or face. These terms are principally employed among Brassicaceous (Cruciferous) plants. Accumulation of Power. Power is said to accumulate when a certain force is exercised upon a body in motion, which is not able to be absorbed by that motion; or when a force is exercised upon a body in repose, which is not capable of relieving the power so accumulating. The measure of the power thus developed is to be found in the capacity of the machinery in action to resist the force thus exercised; or in the vis inertia of the body impressed with the motion, together with any additional efforts it may communicate. The accumulation of force is a great element of the blow with which a heavy body strikes the ground when falling from a height: it is also a matter of serious consideration with the locomotive builder, or the mechanical engineer, in designing their machinery. [GRAVITY; LOCOMOTIVE; STEAM ENGINE.] Accusative Case. That inflection of the noun which expresses the passing over of an action from one substance to another: it consequently follows verbs active in all languages. The English language retains the inflected case only in the pronouns. [GRAMMAR.] Acephalans, Acephala (Gr. àképaλos, headless). A term applied to a class of molluscous animals, comprehending those which are without a head. The class is subdivided, according to the modifications of the respiratory organs, into the 'Lamello-branchiate," Palliobranchiate,' and 'Hetero-branchiate,' or tunicate orders [which see]. The oyster, lamp-cockle, and squirter, or ascidia, are their several representatives. In the system of Cuvier it includes only the lamello-branchiate and hetero-branchiate orders, or the Acephala testacea, and the Acephala nuda. [CONCHIFERA.] Acephali. In Ecclesiastical History, a name given to an Egyptian sect which renounced communion with the patriarch of Alexandria, because the latter had subscribed to the Henoticon of Zeno, A.D. 482. (Gibbon, Roman Empire, ch. xlvii.) Acephalocyst (Gr. à, priv., ¿yképalos, brain, and Kúoris, bag). A hydatid, or sub ACEPHALOPHORES globular or oval vesicle, found in the cellular fissue, and filled with fluid. Its animal nature has been asserted by Kuhn and other zoologists. It is, however, probably a mere form of morbid and dropsical cell. Acephalophores, Acephalophora (Gr. axépaλos, and pépw, I bear). The name given by Blainville to a class of molluscous animals corresponding to the Acephala and Brachiopoda of Cuvier. Acephalous. A Botanical term, occasionally employed to designate ovaries, the style of which springs from their base instead of their apex, as in Lamiacea. Acer (Lat.). A genus of hardy trees, comprehending the common maple, the sycamore, and various kinds of American maples. Their wood is not of much value, being usually light and perishable; but the knotted parts of A. campestre furnish the pretty bird's-eye maple of cabinet-makers. The sap of A. saccharinum is so sweet that sugar of good quality is preA. platapared from it in North America. noides, the Norway maple, is one of the best trees for planting in places exposed to the sea air. Aceraceae. [ACER.] A small natural order of polypetalous exogenous plants, comprehending the genus Acer, and a few others. It consists of trees, or at least of woody plants, inhabiting the temperate parts of the world; their most essential character consists in their samaroid dicarpellary fruit, connected with a broken-whorled calyx, and unsymmetrical flowers without scales at the base of the petals. The uses of the order are the same as those of Acer. Acerans, Acera (Gr. à, without, and Képas, ACETYLE acetabulum signifies the cavity of the hip- Acetal (Lat. acetum, vinegar). A colour- Acetamide. Acetanilide. A crystalline solid derived from aniline by replacement of an atom of hyAcetarious Plants (Lat. acetaria, salad). drogen by acetyle. It is soluble in hot water. Plants used in salading; such as lettuce, mustard and cress, endive, &c. Acetates. [VINEGAR.] Salts containing acetic acid. Acetic Acid. The pure acid contained in vinegar. It is a pungent acrid liquid; its odour, when diluted, is agreeable and refreshing; when perfumed, it is known under the name of aromatic vinegar. Acetic Ether. This liquid is a compound of acetic acid and ether. Its odour somewhat resembles that of apples. It is an odoriferous and flavouring constituent of many wines, and is easily made artificially by distilling a mixture Acetification. The process by which wine, of alcohol, oil of vitriol, and acetate of potash. beer, &c., become converted into vinegar. It consists in the direct absorption of oxygen from Combinations of acetic acid Acetines. the air by the alcohol contained in the liquors. with glycerine. They are oily bodies, and are prepared artificially. Acetometer. A hydrometer used in determining the strength of acetic acids. Acetone (Lat. acetum). When acetate of lime, baryta, or lead, is subjected to dry distillation, a limpid colourless liquid is obtained, to which the above name has been given : it has a penetrating aromatic odour, and is highly inflammable: its ultimate components are 3 atoms of carbon, 3 of hydrogen, and 1 of An oxygen. Aceric Acid (Lat. acer, the maple). acid obtained from the sap of the maple tree. Acerose. The word literally means chaffy (Lat. panis acerosus, chaffy or brown bread). Botanists apply the term to leaves of a narrow, stiff, and pungent nature, like those of fir trees. Acerra (Lat.) A small altar, placed by the Romans near the couch on which a dead body was laid. Incense or other perfume was burnt upon it, originally, no doubt, to correct any offensive smell arising from the corpse. The name was also applied to the incense box itself. Acetabulum (Lat. a vinegar cruet). A term applied to the suckers on the arms of the cuttle-fish and other dibranchiate cephalopods, which have been, hence, recently termed acetabulifera. These suckers were called by Aristotle kotuloi, which Taylor has erroneously rendered 'joints,' in the English translation In Anatomy, of the History of Animals. 15 Acetonine. An alkaline liquid derived from the action of ammonia on acetone. Acetonitrile. A liquid containing the carbon and hydrogen of acetic acid associated with nitrogen. Its more recent name is cyanide of methyle. Acetous Acid. [ALDEHYDIC ACID.] Acetureide. Urea in which hydrogen is replaced by acetyle. Acetylamine, Acetylia, or Diethylenia. An organic base derived from a double atom of ammonia by the replacement of two double equivalents of hydrogen by two of ethylene. Acetyle. The hypothetical radicle of the acetic compounds: it is composed of four atoms of carbon and three of hydrogen. Its symbol therefore is C,H,, and that of the acetic acid CH ̧ ̧. ACETYLENE ACHROMATISM Acetylene. Of all known hydrocarbon gases | μús, a tunic). Plants which have neither calyx this contains least hydrogen. It is present in nor corolla; whose flowers are destitute of all small quantities in coal-gas, and has recently covering. been formed from its elements artificially by passing a current of electricity from carbon points through hydrogen. It is interesting as the starting-point from which a number of organic bodies may be formed. Achæan League. A confederacy which existed from very early times among the twelve towns of the province of Achaia, in the north of the Peloponnesus. It was broken up after the death of Alexander the Great, but was set on foot again by some of the original cities, B. C. 280, the epoch of its rise into great historical importance. From this time it gained strength, and finally spread over the whole Peloponnesus, though not without much opposition, principally on the part of Lacedæmon. It was finally dissolved by the Romans, on the capture of Corinth by Mummius, B. c. 147. The two most celebrated leaders of this league were, Aratus, the principal instrument in its extension, and Philopomen, the contemporary and rival, in military reputation, of Scipio and Hannibal. (Polybius, i. ii.; Pausanias, i. vii.; Thirlwall, History of Greece, ch. lxi.; Freeman, History of Federal Government, vol. i. ch. v.; Clinton, Fasti Hellenici.) Achæne or Achenium (Gr. à neg., and Xaivw, I gape). A small bony fruit, containing a single seed, which does not open when ripe. Achatina. A genus of terrestrial gasteropods, known by the trivial name of agate-snails: characterised by an oval oblong ventricose shell, striated longitudinally; with the aperture ovate and never thickened or reflected, and a smooth, straight columella, truncated at the base. All the species are oviparous, and one, the Achatina Zebra, produces eggs with a hard, white, calcareous shell, and as large as those of the sparrow. Acheron. A river in the nether world of Hades, usually derived from the Greek word axos, as if flowing with pain and sorrow. Two rivers of the same name, one in Thesprotia, the other in Italy, were supposed, from the foulness of their waters, to be connected with this stream. The name probably comes from the root to which belong Achelous, Axius, Oxus, and the many other variations, all expressive of flowing waters. Achievement (Fr. achèvement, from achever, to accomplish). In Heraldry, this term denotes generally a shield of armorial bearings; but is more particularly applied to the funeral shield, commonly called hatchment, affixed to the dwelling-house of a recently deceased person. Achilleine. A peculiar bitter principle procured from the Achillea millefolia. Achilles. [EPIC; HOMERIC POEMS; ILIAD; MYRMIDONS; ODYSSEY.] Achirite. The name given by Werner to Dioptase, after Achir Mahmed, who first brought the mineral from Siberia. Achlamydeous (Gr. à priv., and xxa Achmatite. A variety of lime-and-iron Epidote from Achmatowsk. [BUCKLANDITE.] Achmite. A mineral found near Kongsberg in Norway. It is a double silicate of iron and soda, and is supposed by G. Rose to be an altered form of Pyroxene. Achroite (Gr. à neg. and xpola, colour). The name proposed by Rammelsberg for colourless varieties of Tourmaline. Achromatism. The destruction of the coloured fringes which accompany the image of an object seen through a prism or lens. Light is not homogeneous, but compounded of rays unequally refrangible, and differing from one another in other physical properties. In passing into a refracting medium, some of the rays are more refracted, or bent out of their course, than others; whence the image of an object, seen through a lens, is rendered confused and indistinct, and appears encircled by a coloured ring. This circumstance presented a formidable obstacle to the use of the telescope; and, accordingly, soon after the invention of that instrument, the utmost efforts of mathematicians and artists were exerted to remove the imperfection. The compound nature of light, and, consequently, the theory of unequal refrangibility, were, however, not known till the time of Newton; and after the true source of the difficulty had been discovered, it continued for a long time to be believed that achromatism was impossible, or that light could not be refracted without being decomposed. Newton himself was led to this conclusion by imperfect experiments. Subsequent discoveries have proved that the conclusion was erroneous, and that the rays of light may be bent without being separated; but, after all the progress that has been made in practical optics, as well as in the theory of colours and light, the subject of achromatism continues to be one of the most delicate and embarrassing, both in regard to theory and practice. The principles on which achromatism is effected may be briefly explained as follows. On observing the spectra formed by prisms of different substances, it is soon perceived that the different colours, though always ranged in the same order, do not occupy the same relative lengths. Hence it follows, that the primary coloured rays, in passing through different substances, do not undergo the same relative refractions; that is to say, the angle formed by two rays, the red and the violet, for example, is greater when the light is refracted by some substances than when it is refracted by others, though in all substances the violet is more refracted than the blue, the blue more than the green, and so on. The angle formed between the extreme rays of the spectrum measures the dispersion of the rays; and it is found by experiment that the dispersive power of common flint glass is to that of crown glass in the ratio of about 3 to 2; so that if a prism of flint glass ACHROMATISM ACIPENSER give a spectrum three inches long, a similar | Bavaria by Mertz and Steinheil, and in this Two prisms may therefore be so arranged the one behind the other, that the chromatic effect of the first may be neutralised by that of the second, so as to destroy colour, but still retain a certain amount of refraction. The achromatism of lenses depends on the same principles as that of prisms; but compensation is attended with great practical difficulties, on account of its being necessary to have regard to the spherical aberration. If the ratios of the dispersion of the different spectral colours were all equal, the achromatism would be perfect when the extreme rays, or, indeed, any two rays, emerge parallel. This, however, is not generally the case; these ratios are in general variable, and, therefore, the angle which renders the red and violet rays parallel is not that which is required for the intermediate colours. It is possible, however, to remedy this defect, by combining a greater number of prisms or lenses. Theoretically speaking, indeed, the number of rays united or rendered parallel is the same as the number of prisms. The achromatic object-glasses of telescopes formerly made in this country, were generally triplethat is to say, consisted of three lenses, namely, a concave lens of flint glass placed between two lenses of crown glass; but almost all the large object-glasses lately constructed consist of only two lenses; the achromatism produced by this combination, though not rigorously exact, being sufficient for optical purposes. 1 Achras (Gr. axpás, a wild pear). A genus Achtaragdite. A doubtful mineral found Ore. Acid. In common language, any sour substance; in Chemistry the term is less restricted, and often applied to all substances which saturate and neutralise the alkalis and other salifiable bases, without other obvious acid properties. Acidimeter (Lat. acidus, acid, and Gr. μéтpov, measure). An instrument for determining the strength of an acid by its saturating power: it usually consists of a glass tube graduated into 100 equal parts, and containing an tion of which, requisite to saturate a given quanalkaline liquor of known strength, the propor tity of any acid, is the equivalent of that acid. [ALKALIMETER.] Acidulous. Dim. of acid. Subacid; a term frequently applied to mineral waters containing carbonic acid. The possibility of refracting light without producing colour was discovered and experimentally proved by Mr. Hall, a country gentleman of Worcestershire, under whose directions Acinaciform (Lat. acinaces, a scimitar, and an achromatic telescope was made by a London artist in 1733. But, from whatever cause, no notice was taken of Hall's discovery; indeed, it forma, shape). A name applied to certain sucappears to have been entirely forgotten, and culent leaves and fruits, which resemble the Acineta (Gr. ȧ írna, from à, priv., and contributed nothing whatever to advance sub- blade of a curved sword or Turkish scimitar. sequent researches. The merit of the discovery of achromatic compensation belongs to John Kívnous, motion). A genus of Infusoria, allied Dollond, who arrived at it through a long to Vorticella; and supposed by many authors course of skilful and systematic experiments to be one of the transformations of that genus, undertaken for the express purpose. Its possi- the cyst of which is, according to Stein, converted bility had, indeed, been previously asserted by into an Acineta by the protrusion from its Acinus (Lat., from Gr. ǎkivos, the stone of perthe celebrated Euler, who, reasoning from the exterior of the characteristic knobbed tentacles. a grape). The separate carpels of a succulent construction of the eye, which, indeed, is a fect achromatic instrument, proposed various hypotheses for destroying the coloured images. fruit consisting of many carpels; as the raspAfter Dollond's discovery, the subject was ex- berry. This term is also applied in Anatomy amined theoretically by Euler, Clairaut, and to a cluster of the ultimate secerning follicles D'Alembert, but their profound mathematical of certain conglomerate glands; as the liver. investigations led to no practical improvement. The object-glasses made by Peter Dollond (a son of the inventor) were long celebrated throughout Europe as the best that were manufactured. Of late years, however, the science of light has been vastly extended; and the discoveries of Fraunhofer, in particular, have opened up an entirely new view of the composition of the spectrum. The largest and best achromatic glasses have recently been made in VOL. I. 17 Acipenser (Lat. a sturgeon). The name of a Linnæan genus of the Amphibia nantes, characterised by solitary, lateral, linear gill-openings; the mouth, situated beneath the head, retractile and edentulous; feelers under the snout, in front of the mouth. The sturgeon (Acipenser Sturio), and most of the other Amphibia nantes of Linnæus, form the order ChonC dropterygii, or cartilaginous fishes of Cuvier. The genus Acipenser is separated by Agassiz |