We have confined ourselves to a mere outline of this interesting and extensive family, and the student should consult for the species the works of G. and F. Cuvier, especially the Ossemens fossiles' of the former; of Mr. Hamilton Smith, in Griffith's Cuvier; of Lichtenstein (Saugethiere); and of Richardson (Fauna Boreali-Americana). He should al o refer to the Proceedings of the Zoological Society of London; for, numerous as the species already are, new ones are daily occurring. Other works will occur to the learned, and we ought not to forget the Ruminantia, by Sir William Jardine (Naturalist's Library, 'Mammalia,' vol. iii., 1835), where much valuable information, ably illustrated, will be found.

DEFAMATION; the speaking slanderous words of another. The injured party may bring an action to recover damages, but to enable him to succeed, it is absolutely necessary that the words should contain an express imputation of some crime or misdemeanor which would make him liable to punishment; or, if the words are not actionable in themselves, some special damage should be proved to have resulted from them to the plaintiff. There are certain cases, however, where words are spoken of a tradesman or professional person in the way of his trade or profession, as that a tradesman is insolvent, or that an attorney deserves to be struck off the roll, in which the plaintiff, by reason of the character he fills, may recover damages. Of the first class a recent case affords an illustration. A churchwarden was accused by the defendant of having stolen one of the church bellropes: it was held that, as the property of the bell-ropes was vested in the churchwarden, the words did not impute a crime to the plaintiff for which he was punishable, and consequently that the action could not be maintained. In former times, actions for slander were very rare; and though it has been frequently said that actions for words spoken in heat or anger, suddenly and without deliberation, ought not to be encouraged, yet it has been truly observed (by Wray, Ch. Just.) that unless the party injured by false and malicious scandal had a remedy at law, it would lead to personal violence, and the consequences might be fatal. In most cases, malice in law may be inferred, but in actions for slander prima facie excusable on account of the cause of publishing the slanderous matter, malice in fact must be proved; it is scarcely necessary to observe, that where special damage is proved, the existence of malice is immaterial. Defamation is also punishable in certain cases by indictment and criminal information. Where the slanderous matter is spoken of a peer, the offence is termed scandalum magnatum, and is made punishable by various statutes: this mode of proceeding however may be said to have become obsolete.

The ecclesiastical courts have power to punish for defamation relating simply to spiritual affairs; as an imputation that the complainant is a heretic: but these courts can only inflict punishment by way of penance; they cannot award damages. An action may also be maintained for slander of title to an estate or property; but in this case the plaintiff must prove malice express or implied: it is not sufficient that the defendant should allege title in himself, or make objections to the title of the plaintiff if he had reasonable grounds for so doing. (Cowel; M'Culloch; Selwyn, N. P.) [LIBEL: SLANDER.]

DEFEAZANCE (from the French verb défaire, to make void), is an instrument which defeats the force or operation of some other deed, estate, or interest, upon the performance of certain prescribed conditions. Defeazances are of two kinds, the one applicable to freehold estates; the other, to terms of years and executory estates, and to recognizances, bonds, and other executory interests. The former must be a collateral deed made at the same time with that to be defeated, and forming part of the same transaction. In this manner mortgages were formerly made, the mortgagor enfeoffing the mortgagee, and at the same time executing a deed of defeazance. Defeazances have been discountenanced by the courts, as affording opportunities for fraud, and they are now rarely used as applicable to titles, it being far better to make the conditions apparent on the deed itself. (See lord Talbot's Remarks in Ca. Temp. Talb., p. 64.)

The latter kind of defeazances may be made either at the time of the original transaction, or at any subsequent period

DEFERENT, a circle or oval curve on which the centre of another oval moves, while a planet is supposed to move round the latter. The term is one of the PTOLEMAIC HYPOTHESIS. Thus the earth's orbit, to choose an example out of the modern system, is a deferent on which the moon's orbit is carried. But to make this example perfectly represent the sense in which the word was used by Ptolemy, we must suppose the system of Tycho Brahé to be the real one, and a spectator in the sun assuming the Copernican system.

DEFFAND, MARIE DE VICHY, MARQUISE DU, daughter of Gaspard de Vichy, Count of Champ Rond, was born in 1696. She was brought up to figure in the world, according to the received expression; that is to say, to shine in the saloons of the capital. She had natural parts, wit, playfulness, and taste, which her education tended to stimulate, rather than to form her heart. In 1718 she married the Marquis du Deffand, a colonel, and afterwards general, in the French service. Having some time after separated from her husband, she had her own establishment, her parties, her admirers, and her petits soupers. She lived like many other ladies of rank and fashion of the times of the Regency and of Louis XV., and her correspondence throws much light on the manners of that age. She numbered among her friends and correspondents some of the most distinguished men of France, such as President Hénault, Montesquieu, Marmontel, D'Alembert, Voltaire, &c. After the death of her husband, in 1750, in order to accommodate herself to her reduced income, she gave up her establishment, and took apartments in the external or extra-claustral part of the Convent of St. Joseph, in the Rue St. Dominique, where she spent the remaining thirty years of her life. She continued, however, her evening parties, which were in great repute for wit, pleasantry, and bon ton, and to which most foreigners of distinction who resorted to Paris were introduced. Being afflicted with blindness, she took as a companion and reader an unprotected young person, Mlle. de l'Espinasse; but she afterwards became jealous of her, and they parted; on which occasion Madame du Deffand quarrelled with D'Alembert also. She continued, though blind, to correspond with her friends, and especially with Voltaire and Horace Walpole, to a very advanced age. She died at St. Joseph, in September, 1780, in her 84th year. Madame du Deffand possessed some very valuable qualities: she had real wit and taste without affectation, and much tact and sound judg ment whenever caprice or prejudice did not lead her astray. She had a quick perception of merit of every kind, and her house was always open to it: she had a horror of dogmatism, exaggeration, and pedantry: although a free-thinker, she never partook of that absurd fanaticism against religion which characterized some of the philosophic writers of the eighteenth century. Her judgment was too calm and sober not to perceive the inconsistency of philo.0phical intolerance; she even gave some good advice to Voltaire on this subject, and was one of the very few who spoke frankly to him. In her correspondence with Walpole she judges Voltaire rather severely. 'Correspondance de Madame du Deffand avec M. Walpole de 1766 à 1780, suivie de ses Lettres à M. de Voltaire de 1759 à 1775,' 4 vols. 8vo., Paris, 1810; and also Correspondance inédite de Madame du Deffand avec D'Alembert, Montesquieu, le Président Hénault, &c., suivie des Lettres de M. de Voltaire à Madame du Deffand,' 2 vols. 8vo., Paris, 1809, with a biographical notice.

DEFILADING, is that part of fortification the obje t of which is to determine (when the intended work would be commanded by eminences within the range of fire-arms), the directions or heights of the lines of rampart or pa apet, so that the interior of the work may not be incommoded by a fire directed to it from such eminences.

If it be required, with a given height of parapet, to approach obliquely as near as possible to an eminence, the following process is adopted, the situation of the rampart or parapet at that extremity of the intended line which is farthest from the eminence being also given. A line is sup

posed to be drawn from the commanding eminence, or rather from a point about eight feet above it, through another point which represents the crest or summit of the intended parapet at the given place, and to be continued till it intersects the natural ground in rear of that part of the line of parapet. This crest is considered as the vertex of a cone whose base is a circle, on the ground, having for its radius a line equal to the distance from the parapet to the rear extremity of the ground to be protected (which distance, however, must always be less than that of the intersection above mentioned). Then a line being drawn on the plan, from the point vertically under the given crest, parallel to a line drawn from the said intersection and touching the circle, will be the direction of the intended rampart or parapet, whose height must be everywhere equal to that which was given. By this construction all the lines of fire from the commanding eminence, and passing closely over the crest of the parapet, will be in a plane meeting the ground on that eminence, and touching the convex surface of the cone.

Again, if it be required, when the plan of the work is determined, to ascertain the heights of a rampart or parapet in different places, so that the interior may be protected from the fire of the enemy on a commanding eminence beyond, the relative heights of the principal inequalities of the ground with respect to some horizontal plane, technically called the plane of comparison, (which generally passes through the highest or the lowest point) must be found by the spirit level. An oblique plane, technically called the plane of site, must be imagined to touch the summit of the eminence in front, to pass above all the intermediate ground, and to meet that in rear of the work; then the relative heights, with respect to the plane of comparison, of the several points in the plane of site which are vertically above the inequalities before mentioned of the natural ground, must be computed, and the differences (which express the heights of the plane of site above the natural ground in such places) being added to the given height which the rampart or parapet is to have above the plane of site, the sums will express the heights to which the works are to be raised above the natural ground at the same places.

When the work is of small importance, the elevations of the parapets above the ground are generally determined by the eye-thus:-Pickets are planted in convenient places, chiefly at the angles of the intended work (the plan of which has been already traced on the ground,) and on the summit of the commanding eminence, the picket in this place being about eight feet high. The visual rays being supposed to proceed from the top of this picket to two or more points, which must be also eight feet above the ground, in rear of the work, the intersections of these rays with the pickets planted on the magistral or ground line of the work, will show the heights to which the parapet is to be raised at those places in order that the interior may be effectually protected.

A similar process is employed when it is required to protect the defenders of any parapet from the fire of the enemy on a commanding eminence in their rear; in which case it is frequently necessary to raise, in the interior of the work, a mass of earth, which is called a traverse or a parados, according to its situation.

DEFILE, in military writings, is a name given to any narrow way. Every piece of ground which, in consequence of local impediments, can be passed by a column only on a narrow front, is called a defile. Such are roads along valleys, between walls or hedges, or over dykes raised across marshes. Sometimes also the term is applied to a street in a village, and to the path over a small bridge.

DEFINITION (definire, to mark out a boundary,) is the process of stating the exact meaning of a word, by means of other words. From so boundless a subject, we can only select a very few points, such as have reference to the most common uses of the term. In the first place, it is evident that all definition contains a species of fallacy, if considered as an absolute determination of the meaning of words. Quis custodiet ipsos custodes? who shall determine the meaning of the words which make up the definition? The process of definition can never appear satisfactory unless it be considered as a transition from many words to the single term which it is agreed shall stand for their meaning, be that what it may. All attempts at absolute definition must end in confusion of ideas.

But at least, perhaps it may be said, the matnematea. sciences are founded upon exactness of definition. Nothing is more common than this assertion coupled with another, namely, that these sciences depend entirely upon definitions. In a certain sense both are true, but that sense is not the most frequent meaning of them. The exactness of mathematical definition is not of arbitrary construction, but a consequence of the exactness of the notions which all men have, or may be made to have, upon the things which the words represent. There is no exactness in the fundamental definitions of mathematics, verbally considered, but only much confusion arising from the attempt to introduce conventional accuracy. The words straight line' carry with them their own meaning, and even explain the attempt which is made to explain them; for no one would easily guess what sort of line it is which lies evenly between its extreme points,' unless he were aware that it is a straight" line which these words attempt to describe.

Definition may be purely nominal, or it may be such a description of the thing defined as amounts to a statement of some one of its fundamental properties. The first we see in the words isosceles triangle, the definition of which is a simple annunciation that we intend to use a Greek term. The second may be seen in the article CONCAVE AND CONVEX, in which the definition is made by means of an absolute mathematical property of the thing defined: the relative position of the spectator, the curve in question, and a straight line, do not enter into the notion which the words immediately suggest. The method of Euclid is to supply a rough and descriptive definition addressed to the common notion of the word, followed by an assumption of a ma bematical property under the shape of an axiom. Thus a straight line is that which lies evenly between its extreme points;' while the real definition, or distinction between straightness and the contrary is contained in the axiom two straight lines cannot enclose a space.' Every attempt at mathematical definition, which does not rest upon the selection of a substantive property of the thing defined, to be the test of its existence, is either the mere sub-titution of words for words, or an attempt to make that mere substitution effect something more than lies in it to perform.

The conditions of a good definition are, 1, perfect axio matic evidence that the property which is made the distinguishing test belongs to the object intended to be defined, and to nothing else; 2, entire separation of the part of the property, if any, which admits of being demonstrably connected with the notion defined, from that which contains the assumption; 3, the introduction of the definition in the proper place, namely, when the necessity for a new verbal representation has begun to appear.

DEFLAGRATION is a term einployed to denote the sparkling combustion of substances without violent explosion: thus when nitre and sulphuret of antimony are mixed and ignited or thrown into a hot crucible, the combustion which occurs is of the kind termed deflagration.

DEFLECTION. A term applied to the distance by which a curve departs from another curve, or from a straight line; and also to any effect either of curvature or of disc.ntinuous change of direction. It is used where any bending off' takes place, which is in fact the etymological meaning of the word.

DE FOE, DANIEL, the son of James Foe, a butcher in the parish of St. Giles, was born in London, in 1651. Of his youthful years we have nothing particular to relate. His father, who was a dissenter, sent him to a dissenting academy at Newington Green, where he remained four years. As the only education he received was at this time, we may conclude that he applied with considerable advantage. Different reasons have been assigned for his prefixing De' to the family name of Foe: the true cause of his doing so was probably a desire to conceal the lowness of his origin, and a belief that this addition would effect the object. De Foe first appeared as an author in 1653, when he published a political pamphlet on the war that was then carried on between the Austrians and the Turks, Two years afterwards, his aversion to James the Second and his government and his zeal for the maintenance of Protestantism induced him to enlist under the duke of Mon mouth, whose rash and ill-concerted conspiracy was the cause of so many executions. Our author had the good fortune to escape the fate that numbers of his companies suffered. De Foe had for some years been engaged in