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from the vertex, we have repulsion; let the obtuse angle be increased to 180°, and in this extreme case the two currents merge into one: hence it follows that the consecutive parts of one and the same current exercise a mutual repulsion on each other.

The actions exercised by a rectilineal current and by a sinuous current, which have generally the same direction and are terminated at the same extremities, are equal, the intensity of action being supposed the same in both cases; thus, if we suspend a moveable conductor between a rectilineal and a sinuous conductor disposed so as to repel the first, this, after a little oscillation about its mean place, will finally rest in the middle of the interval between the conductors.

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of equilibrium in a plane parallel to the indefinite con-
ductor.
Instead of a single closed circuit we may suppose any
number of them connected together after an invariable
manner. The action of an indefinite current will still tend
to bring that system into a plane parallel to its direction
These systems have been called electro-dynamic cylinders,
and also canals of currents.

In consequence of the electro-chemical causes which are so widely diffused through the globe, electrical currents are generated, which give its polarity to the magnet, and which, as is well known, are sufficient to generate continued rotation of given currents.

It has been found by Ampère that the actions of similar conductors on points similarly situated are equal; and that a closed conductor exercises no action on a circular conductor moveable round a central axis.

In seeking for the true laws of elementary action of currents, a decomposition similar to that of the parallelipiped of forces may be employed; that is, for the action of an ele mentary current we may substitute the actions of the three sides of a parallipiped terminated at the same extremities; for, as before stated, if we preserve the direction of the currents we shall not alter the action by substituting any sinuous for a plane conductor with the same extremities.

We will now show how the law of force between the elements of currents may be obtained, which, when once known, will reduce all the phænomena to mathematical

calculation.

To determine the law of force tending to or from any element of an electrical current, when points of another current are taken at different distances but in a given direction:

Let ds, ds' be the elements of two electrical currents, of which the intensities are i, i', their distance a unit, and f the force mutually exercised in the line forming their middle points; hence fii' is ds.

Let us now consider the action of an indefinite current AB, on a terminated current CE, which is directed towards E; the direction of AB being that indicated in the figure. The portion BE of the indefinite current repels EC, in consequence of the contrary direction of the current in the latter. Let us represent this force in magnitude and direction by Cg=CG; also AE attracts CE; the force may be represented by CF, similarly situated with CG; but Cg, the repulsive force of BE, is drawn without the angle BEC; and CF, or the attractive force of AE, must be drawn within the angle AEC. If we now compound the forces CF, CG, they will manifestly produce a resultant CH parallel to the indeLet do do' be portions of similar currents to the former, finite current AB. Hence the terminated current will be but of which the linear dimensions are times as great, and urged by a force parallel to the other, and in a contrary since their mutual distance is also times as great; this direction; and by similar reasoning it is easily seen that if force is diminished in proportion to some function of v, as the direction of the current CE were contrary to that indi-(v): hence ƒ' = ii' dø, do'. p (v). cated by the arrow, or receded from AB, then the whole force in CE would be in the same direction as the current AB, and parallel to it.

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Now do = 1

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1

Hence = v24 (v)

=

dev ds'; therefore f'ii' v ds ds'. 4 (v).

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of the distance, as in statical electricity; but we must observe that the directions of the currents are here supposed to make given angles with the joining line v.

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The following theorems are taken from Mr. Murphy's Electricity,' to which we refer for the demonstrations, which are by no means difficult to persons a little acquainted with the differential and integral calculus.

Let a right line join the middles of the elements ds, ds' of two currents, being inclined respectively to those elements at the angles 0, 0', the planes of which angles are mutually inclined at an angle p, and let p, p' be the intensities of the currents; the mutual action of these two elements will then be represented in all cases by the formula pp'ès ds' {

22

sin e, sin e' cos cos 0 cos

- d v ds

:(

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Let us suppose CD to be a conductor moveable round an axis at C in the plane DD'D", and suppose the direction of its current to be from C towards D, and that of an indefinite conductor AB to be similar and parallel; then AB attracting CD will turn it round C into the position CD', and the force on the angle CE'B is then repulsive, and in CE'A attractive; hence CD' will further turn round, and the same direction of rotation will be continued in the upper semicircle; for the force is attractive in the angle D""E"B, and repulsive in D'"E""A. Hence a continued rotation will be produced. This rotation will be in the contrary direction if we change the direction of the current either in AB or CD; or if, without changing the current, we transfer AB to the opposite side of CD: hence if AB be placed so as to meet the axis C, there will be no rotation; hence also if the terminated current be moveable round its middle point there will be no rotation, since both its halves tend to rotate in contrary ways. It is easy to analyse in the same manner the action of an indefinite conductor on a closed current Dy considering its action on each of the parts, the general This may be easily deduced from the preceding formula.

effect being to bring the moveable conductor into a position

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dr ν ds'

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exerts no longitudinal action on & s'; only a normal force. This coincides with what has been before shown for the action of an indefinite current on a terminated conductor. The same property holds true for a closed current, since in this case 0=0, R=R1.

From hence it is easy to find the total action of a fixed current, or a moveable rectilineal current.

The action of a closed current, or an element of another current, which is turned in all possible positions round its middle point, lies in an invariable plane.

The mutual action of two small closed conductors, containing areas A, A, the centres of which are at a distancev, exercise on each other a force directly as the plane areas, and inversely as the fourth power of the distance.

cising a tangential force. Before this time a connexion between electricity and magnetism had been suspected, or rather believed, by Franklin, Beccaria, and others, from the well-known circumstance that the poles of the compassneedle had been frequently reversed during thunder-storms, and that the same effect could be produced by electrical discharges. In most experiments which were then made these discharges were unnecessarily strong; but to Oersted's discovery, followed up as it has been by Ampère, Faraday, Barlow, Arago, &c., we must ascribe the source of those accurate data by which the actions of the earth on magnets, of magnets on each other, of conducting wires on magnets, and of the earth on conducting wires, are reducible to similar and simple principles of action. x-When a magnetic needle is placed near a conducting wire in the plane of the magnetic meridian, and the battery is powerful, it is observed that the needle will turn round, placing itself at right angles to the direction of the current; the same effect, which we have seen in the preceding article, would be produced by the same conductor on a canal of currents. If we suppose that a man with his face turned to the needle is himself the conductor, with his feet at the positive pole, the north pole of the needle will turn towards his right. This must be understood as only meant to illustrate the direction of rotation.

The action of a uniform canal of currents indefinitely extended in one way varies inversely as the square of the distance of its extremity from the element acted on, and directly as the sine of the angle which that distance forms with the element, and is in a direction perpendicular to the plane passing through the element and the extremity of the canal.

When two uniform and indefinite canals of currents act on each other, the canals being supposed terminated at one extremity only, the resultant is in the line joining their extremities, and the force is inversely as the square of this line: hence the action of finite canals may be easily estimated, as being the difference between two indefinite canals. With respect to the nature of the force, it will be attractive or repulsive as before described. The simplest mode of observing the actions of a canal of closed currents is by twisting a wire in the form of a helix having but small intervals between the successive convolutions, the action of each portion of the helix being then very nearly the same force as that of a portion of a circle or closed current.

Ampère imagined an ingenious manner of calculating the actions of any plane closed conductors. Conceive one such to be divided into an infinity of small compartments by right lines parallel to the rectangular axes of co-ordinates, and the periphery of each compartment to be traversed by currents, in the same manner as the whole curvilineal side which encloses the area; then it is easily seen that all the internal sides of the compartments, being traversed by two currents in opposite directions, will have no electro-dynamical action, and therefore the sole remaining current is that which circulates in the periphery of the given figure; but by this division into compartments we can calculate the mutual actions of the two closed conductors from the very simple law which we have already given for the action of small closed conductors on each other.

Voltaic conductors, of which the centres of gravity are supported, undergo terrestrial action, similar to that produced by a canal of currents. We should infer, by the position which the moveable conductor takes, that the direction of the terrestrial currents is nearly from east to west, having the north magnetic pole situated on their right.

Since the action of closed currents on an element of a conductor is perpendicular to that element, hence a straight conductor fixed at one extremity, and free to move in a horizontal plane, will receive a continued rotation from the influence of the currents of the earth; but if the conductor were supported by its centre of gravity, it would be brought by their action into a fixed plane, and an electro-dynamic cylinder would come into a position perpendicular to that plane.

All these results of theory are confirmed by experiments, and are shown in the lecture-rooms of gentlemen who profess this branch of science.

There are few works expressly on this subject beside those quoted, the subject being itself the most modern addition to the exact sciences.

ELECTRO-MAGNETISM. The first important discovery in point of time, which laid the foundation of this new science, was made by Professor Oersted of Copenhagen. By reference to the article ELECTRO-DYNAMICS it will be seen that when the wires which communicate with the poles of a galvanic battery are connected by a conductor or by being brought into contact with each other, the opposite electricities thus continually made to combine acquire a power of action on another conductor under similar circumstances, though latent with respect to common electrical action; but this discovery of Ampère was preceded by that of Oersted, who found that the electrical current thus generated acted upon a magnetised bar, and tended to turn it round as if exer

In order to discover the law of action of a current on a magnetic element, Biot and Savart used a small magnetic needle, guarded from the agitations of the air, and having the action of terrestrial magnetism neutralized by a bar, thus subjected only to the immediate action of the conductor. Having acquired the position indicated by Oersted, the times of its small oscillations were observed, which we know by the principles of Dynamics must be inversely proportional, cæteris paribus, to the square root of the accelerating force impressed. By observing the times in which, for instance, ten oscillations of the needle took place, at different distances, it was deduced. without difficulty, that the electro-magnetic force exercised by the whole conductor was inversely as the distance of the needle from the conductor: this of course supposes that the current may be regarded as indefinite, compared with the dimensions of the needle. Hence it easily followed, as was shown by Laplace, that the force exercised by each element of the conductor on the magnetic needle must, like all known forces, vary inversely as the square of the distance; and Biot showed that, when the distance was given, the force was then proportional to the sine of the angle formed by each element of the current with the right line joining the middle of that element with the middle of the needle.

It has been shown by means of the multiplier that the electrical intensity of the current at different points of the same conductor is constant. We may observe that the principle of the multiplier consists in bending the wire in the form of a helix, but returning upon itself so as to form a closed circuit, the wire being covered with silk to prevent communication at the crossings; the action of such a spiral being similar to that of closed circular currents equal in number to the spiral convolutions.

It was afterwards found that the magnetic needle of the multiplier could be acted on by electrical discharges from a Leyden jar; and Mr. Faraday showed conclusively that, with the condition of time, ordinary electricity can produce a continued deviation of the needle; this condition he fulfilled by making the electricity pass through imperfect conductors.

Arago observed that small fragments of soft iron were attracted by the conductor of the galvanic pile, and the same current imparted permanent magnetism to small needles of steel. The needle should be placed perpendicularly to the joining wire or current, or, which is better, be introduced in a helix, the discharge of the current through which instantaneously magnetises the needle.

Nobili observed that needles placed between the isolated spires of a plane spiral of copper wire were, by an electrical discharge, magnetised in opposite ways, when near the centre and when near the circumference. Savary also observed that when needles were placed horizontally with their middle points vertical over a horizontal current and the needles perpendicular to the direction of the current, they were differently magnetised according to their distances. These experiments he has varied relatively to the length of the needles, the length and diameter of the con ductor, &c.

The magnetising force of the current is transmitted without sensible loss through isolating media, as glass, wood, &c., but is much altered by the interposition of conducting plates, a result similar to the development of ordinary electricity by the influence of electrised bodies. Thus :

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Coulomb, to which we have had occasion to refer in the articles ELASTICITY and ELECTRICITY. The following is a description of this delicate instrument.

A very fine metallic wire, or, which is better, a single thread of silk taken from the cocoon, is fixed at the upper A large plate interposed between the conductor and the extremity, and at the lower it supports horizontally a fine needles weakens the magnetising effect of feeble discharges, needle made of a good non-conducting substance, as gumwhile it augments strong ones; and for a given charge, a lac, to one of the ends of which is attached the body to be thin and a broad interposed conducting plate may produce electrised, as for instance a small ball of elder-pith; at the contrary effects, and with a certain determinate breadth the top of the suspended string there is placed a plate moveable effect would be unaltered, and in general the two surfaces with friction on a glass cylinder, in which the thread is conof the same plate exercise contrary actions. (Savary.) tained, by which any requisite torsion may be given to the When a bar of soft iron, bent in a horse-shoe shape, is encom- thread, which is shewn by an index on a micrometer screw; passed by a helix covered with silk and always turned in the the body of the large cylinder which encloses the needle is same way, it may be made to receive a powerful magnetism also surmounted with a graduated brass circle. In elecunder the influence of a current through the helix dis-trical experiments the index of the micrometer is on its charged from a voltaic battery. Mr. Watkins has made division zero, and the plate is turned round to bring the some valuable experiments on the conservation of the mag-needle and pith-ball to the zero of the graduated circle on netic power in soft iron, for which see Phil. Trans., 1833. The discovery of the currents produced by volta-electric induction is due to Mr. Faraday. With about 203 feet of copper wire he formed each of two helices, and twisted them about a cylinder of wood, making one in communication with a galvanometer and the other with a powerful voltaic pile. The moment the communication was established, the galva-needle being moveable with it, carries it round through a nometer deviated; then, after some oscillations, returned to its place, and again deviated the instant this communication was broken: hence the directions of the inducing and induced currents are contrary, while that generated at the interruption of communication or cessation of the inducing current is directed the same way with the latter.

the string. Again a second ball is attached to the extremity of a fine isolating cylinder inserted in the apparatus so that both balls may be in contact without pressure. The balls are then electrised by communication with some isolated and electrised body, and acquiring similar electricities repulsion immediately takes place. That attached to the certain angle, and after some oscillations settles at a definite position with respect to the fixed ball, this angle being indicated by the graduated arc; the elastic force of torsion is then in equilibrium with the moving force of repulsion between the balls, and hence a measure of the latter can be obtained. In such experiments only a very small electrical charge is communicated to the balls.

The same philosopher has also succeeded in producing currents by the influence of magnets, his experiments with Coulomb, in seeking the law of electrical action, found the great magnets of the Royal Society proving most mani- that in the first instance of his experiment the needle defestly the disengagement of electricity by the influence of viated by 36°. Then, communicating a torsion to the thread ordinary magnetism. The extraction of the electrical spark in a direction tending to diminish this deviation, he found from the magnet is now pretty generally exhibited, as also that the micrometer index traversed 126° to reduce the the continued rotations produced by terrestrial magnetism. angle of deviation to 18°, and 567° of torsion was necessary The theory of Ampère, which supposes electrical currents to to bring it to 84; the thread being twisted by forces apexist round the component particles of magnetised sub-plied at both ends it is evident that the entire torsions in stances, and round the mass of the earth, is perhaps the the two latter cases are 126°+18° = 144° and 567+83=5754°, most satisfactory explanation yet given of the cause of mag- while in the first case it is only 36°. By comparing the netic action, and has been greatly strengthened by the dis- deviations with the torsions, it was easily seen that the coveries of Faraday on electro-magnetic induction, by which force of repulsion varied inversely as the square of the dismany objections that had been urged against this theory tance between the balls. It should be remembered in such are removed. experiments that if the torsion of the thread be too great, its elasticity will act imperfectly, and be no longer proportional to the angle of torsion. [ELASTICITY.]

This branch of science is daily receiving constant accessions, and it is gratifying that much of its progress is eminently due to our countrymen. The labours of the French and German philosophers have also been far from unfruitful.

In like manner the law of attraction of differently electrised balls was ascertained, the torsion being then employed in resisting the attraction. We may observe here that the results thus deduced are necessarily approximative, and not exact, because the neutral electricity of the balls being partly decomposed by the mutual influence of the electricities communicated, the small forces thus arising interfere with the actions which should be due to the latter only. The attractive and repulsive forces may also be estimated by disturbing the needle a little from its position of it makes in a given time, as was adopted by Biot in determining the law of electro-magnetic action of a galvanic current.

The following works may be consulted on this subject: Gilbert's Annalen; Memoirs by Erman of Berlin, Prechtl, Hansteen, &c.; and in Poggendorf the papers by Seebeck, Kupffer, &c.; the recent volumes of the Philosophical Transactions, containing Faraday's Researches, Professor Cumming's Electro-Dynamics, and his papers in the Annals of Philosophy; Barlow's labours described by himself in an article of the Encyclopædia Metropoli-equilibrium, and observing the number of oscillations which tana, &c.

ELECTROMETER. This term strictly applies only to instruments adapted to measure electricity; it has however been applied in a more extended sense to those which only indicate the presence of that fluid; but these are more correctly denominated electroscopes.

Of the former kind is the Balance of Torsion invented by

The proof-plane also used by Coulomb was merely a small disc of gilt paper fastened to an isolating handle; this he employed to discover the distribution of electricity on the surfaces of bodies by touching them with the plane at various points, and observing by means of the torsionbalance the quantity of electricity taken up by contact, which he assumed to be proportional to the quantity of electricity at the point touched. Mr. S. Harris has lately thrown doubt on the exactness of this assumption.

Various instruments have been constructed for estimating approximatively the total quantity of electricity in the charge of an electrised body, such as Lane's, Henley's, and Cuthbertson's electrometers. The most precise instrument of this description is one recently invented by Mr. Harris, who is always distinguished by the beautiful precision of his experiments; its description will be found in his paper on electricity in the Philosophical Transactions.'

Electroscopes indicate the presence of very small quantities of electricity, and therefore are generally used with a condenser; as the gold-leaf electroscope, consisting of two small portions of gold-leaf laid flat together; and when

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made to communicate by a conducting stem, with a con-
denser which has acquired electricity from a very feeble
source, they diverge from each other. They have been also
employed to indicate atmospheric electricity. [METEOR-
OLOGY.]

Similar instruments have been constructed for the pur-
pose of indicating the existence of electrical currents of but
slight intensity, such for instance as those generated by
inequality of temperature. [GALVANOMETER and THERMO-
ELECTRICITY.]

ELECTRUM, from the Greek electron (ñλεктρov). Pliny says this term denotes two substances, namely, amber and a metallic alloy composed of four parts of gold and oue part of silver. Ubicumque quinta argenti portio est electrum vocatur.' (Hist. Nat., lib. xxxiii., section 23; Hardouin, tom. ii., p. 19.) The term electron, in the Odyssey of Homer, is supposed to mean amber.

The metallic electrum was in use in the Roman times: it is uncertain whether it was known to the Greeks. The Romans were partial to it for its brilliancy. Pliny, a few sentences lower down than the passage just quoted, says, Electri natura est ad Lucernarum lumina clarius argento splendere.' The Romans used it frequently for what we term plate.

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Lampridius, in his Life of Alexander Severus, remarks, that this prince caused coins to be struck in honour of Alexander the Great, both of electrum and gold. Alexandri habitu nummos plurimos figuravit: et quidem electreos aliquantos: sed plurimos tamen aureos.' (Hist. Aug. Scriptores, p. 922.)

Isidorus, in his Origines (li. xvi., c. 23), speaks of three sorts of electrum:-1, amber; 2, a metal so called, found in a natural state; and 3, a metal compounded of three parts of gold and one of silver.

ELECTUARY, a term applied to a compound of various medicines, united by means of syrup, or wine, and formed into a soft mass, nearly of the consistence of honey. Substances in the state of powder or extract were thus combined, and rendered capable of being swallowed without their natural taste, which might be unpleasant, being perceived. Formerly electuaries consisted of a great variety of ingredients, often very unsuitable to be taken together. In the present day the few electuaries which are prescribed are much simpler in their composition. Many compounds which were formerly preserved in a soft state are now kept in a hard dry condition, and termed confections.

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ELEDO'NE. [CEPHALOPODA; SEPIADE.]
ELE'GIT, so called from the entry of its award upon the
roll, quod elegit sibi executionem' (because the plaintiff
hath chosen the writ of execution), is a writ of execution
given by the statute 13th Edw. I., cap. 18, to parties re-
covering upon judgments for debt or damages, or upon the
forfeiture of a recognizance in the king's courts. It is
directed to the sheriff of the county where the defendant's
property lies, commanding him to make delivery of a moiety
of the debtor's lands and all his goods (except oxen and
beasts of the plough) to the plaintiff.

The sheriff, immediately upon the receipt of this writ,
empanels a jury, who appraise the debtor's lands as well as
his goods, and if the goods alone are insufficient to pay the
debt, then the sheriff, upon the finding of the jury, sets out
one-half of the lands by metes and bounds, and delivers
them over to the party suing out the writ, who thereupon
becomes what in law is termed a tenant by elegit, and
continues to occupy them until the whole of his debt and
damages are satisfied. The tenant's interest in the land is
only a chattel, and as such goes to his personal represen-

tatives.

In like manner every subsequent judgment creditor takes a moiety of what is left; the last moiety being reserved according to the feudal law for the lord to distrain for his services.

Previously to the passing of the statute above referred to, a judgment creditor could only have obtained satisfaction of his debtor's goods by the writ of fieri facias, and of the present profits of his lands by a levari facias; but as the latter writ did not extend to the possession of the lands themselves, a defendant might, if he thought proper, alien the property, and thus oust the plaintiff of his remedy.

Copyhold lands are not liable to be extended under an elegit; but all estates in fee-simple in possession, all estates in reversion, expectation, leases for lives or years (in which case the creditor takes half the rents), an estate tail during

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the life of the tenant in tail, who is the debtor, a rent charge, and a term of years, are liable to an elegit.

When the judgment is satisfied out of the extended, that is, estimated value of the estate, the defendant may recover his lands either by an action of ejectment, or by a suit in equity. If the lands are recovered by ejectment, the plaintiff only accounts for the extended value of the land, which is usually below the real value; and he is not entitled to any interest on his judgment. If, on the other hand, a bill in equity is filed, the plaintiff is allowed interest, and accounts not merely for the extended value, but for the actual profits of the lands during his possession, and it is referred to a master of the Court of Chancery to ascertain the exact amount of such profits. (Reeves's History of the English Law; Archbold's Practice.)

ELEGY, from the Greek, élegos (EXɛyog, whence MXcycïov), in English commonly means a short poem composed on some person's death; also, in a more general sense, any mournful or serious poem, as, for instance, Gray's Elegy in a Country Church-yard. The Greek word, élegos, is properly a strain of lament; elegeion, the form of versification in which such strains were first composed by the Greeks; i. e., the combination of an hexameter and a pentameter (commonly called long and short) verse; elegeia, a poem made up of such verses. (Müller, Hist. of Lit. of Greece.) The elegiac was the first variation from the hexametral, or epic, measure; and this change of form corresponded with a change of subject: the poet in epic composition keeping himself and the workings of his own mind out of sight; while, on the contrary, the free and full expression of the poet's feelings, as affected by external circumstances, constituted the essence of the Greek elegy. Hence arises its variety; the elegies of Callinus and Tyrtæus (the earliest) being political and warlike; of Mimnermus, contemplative and melancholy; of Theognis and Solon, moral and political, &c. It was at first more peculiarly appropriated to social meetings, and therefore equally fit for topics of political and local interest, and for those which refer to the common feelings of our nature, as love, regret for the perishableness of human things, exhortations to the enjoyment of the present hour, and the like. The elegiac was also a favourite measure for epigrams, that is, taking the word in its proper sense, inscriptions. [EPIGRAM.]

Catullus is the first Latin elegiac writer of any note; he was followed by Tibullus, Propertius, and Ovid, with many others of the Augustan age, whose poems are either totally lost, or have only come down to us in fragments. With them political and moral subjects find no place; the elegiac verses of Catullus (a small part of his poems) are, for the most part, either mournful or satirical; those of the other poets above named are chiefly devoted to love, fortunate and unfortunate. Ovid, however, has taken a wider scope of personal feelings in his Epistles from Pontus, and of historical and mythological learning in his Fasti.

ELEMI, a resin, of which there are two or more sorts, brought from different parts of the world, and apparently produced by different kinds of trees. The West Indian or American elemi is commonly referred to the Amyris elemifera (Linn.), but the very existence of such a species is doubtful, unless it be synonymous with the Amyris Plumieri. (Dec.) The East Indian elemi is obtained from the Amyris zeylanica (Retz.), while a third sort, called African, or elemi verum, is referred to the Eleagnus hortensis. A substance resembling elemi, and capable of being applied to similar purposes, may be procured from several plants. West Indian elemi occurs in irregular-shaped small pieces, which run into masses, of a yellowish colour, of an agreeable odour, which is most perfectly developed by the application of heat. The consistence is at first soft, but it hardens with age, and even becomes brittle, losing some of its odour. Specific gravity 1.083. It seems to contain a principle termed Elemine. Elemi is recommended as an ointment, but it is chiefly used to form pastilles, or to burn as incense.

ELEMENTARY ORGANS, in plants, are those minute internal parts out of which all the visible organs are constructed; they are always too small to be seen without the assistance of the microscope, and often require very high magnifying powers to be distinctly observed. When of a spheroidal figure 5000 of them have been sometimes computed to lie in half a square inch; and when tubular they are often not more than of an inch in diameter; their size is however extremely variable, and their magni tudes are given only to convey an idea of their smallness.

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These organs may be defined to be closed, transparent, | terests and feelings, and in which the predominant desire thin-sided membranous sacs, varying in form according to is not the exhibition of truth, but merely the obtaining of the part of the plant in which they are placed, and the pur- victory; for a disingenuous disputant when excited, and pose they serve. conscious of the superiority of his adversary's arguIf for the conveyance of fluid matter equally in all direc- ment, strives to elude conviction by the stratagem of detions, and for the general purposes of digestion and respira-ploying, and seeks to gain a sinister advantage and triumph, tion, they have a spheroidal figure shaped into a polygon by proving or disproving, not the real proposition in quesby the pressure of the sacs upon each other, and constitute tion, but one or more which in some way are apparently common cellular tissue; if fluid is to be conveyed more involved or implied, so as to create the assumption of idenin one direction than another the spheroids are lengthened tity. The following instance is given by Dr. Kirwan (Essay in that direction, and prismatical cellular tissue is the on Logic, vol. ii., p. 440): Paschal arguing against atheism result, or muriform if they are placed horizontally and insists that it is more dangerous than theism, whereas the strongly compressed from the side; sometimes instead of point in debate is the truth, and not the prudence of either being prismatical they are lengthened into bags acute at system. Some Christian sects use similar arguments. each end, the clostres of some French botanists, and the Mistake or misrepresentation of the question to be detertissue thus formed is named prosenchyma, in contradistinc- mined, and the consequent proving of what is not to the tion to parenchyma, which is a collective name for all cel- purpose, are also common in didactic and conversational lular tissue the ends of whose sacs are truncated. Now and discussions, and the sophisms of Petitio principii and non then a fibre is generated spirally in the inside of a sac of causa pro causa are frequently combined with the Ignoratio cellular tissue, but for what purpose is unknown. elenchi. In all cases of irrelevant conclusion, when something is proved which does not in reality contradict the adversary's proposition, the latent fallacy is best exposed by showing that both propositions may be equally true (Archbishop Whateley's Logic, p. 235, 5th ed. 1834); and the best means of preventing sophistical deception of this nature is to keep the attention constantly fixed upon the precise point of dispute, neither wandering ourselves, nor suffering our opponent to wander or make any substitution. (Dr. Watts's Logic.) In dramatical writing the Ignoratio elenchi, or as it is otherwise called, the quid pro quo, is frequently adopted as a very effective expedient for the production of laughter. Numerous and long continued instances of consistent dialogue, displaying the most ingenious and amusing équivoque or cross-purposes, are to be found in the comedies of Molière, the source of amusement being in each party's 'ignorance of the question' about which the other is concerned.

If the elementary organs are for the conveyance of air they are lengthened into tubes, the sides of which are protected in the inside by a fibre, or fibres twisted spirally, so that the threads touch each other, thus forming a lining to the membrane and preventing the ingress of fluid through the sides. Such organs are called spiral vessels, and are exclusively (except in a very few cases) stationed around the pith of exogens, in the woody bundles of endogens, and in the veins of the leaves and of all the parts of the flower. They unrol with elasticity when stretched; and even uncoil with the growth of the membranous tube in which they have been generated so as to leave spaces between the threads through which fluid percolates; they then become ducts, and probably cease to convey air, but become passages for fluid.

If they are required to serve the two purposes at once of conveying fluid along the plant and of strengthening and protecting the parts in which they are placed, the sacs become fine tubes, thick-sided, elastic, tough, and collected in bundles so as to bend any way without breaking; this occurs in wood, which is composed principally of them, and which gives them the name of woody tissue, in the liber, and in the veins of the leaves where they are placed around the spiral vessels.

For an explanation of the many varieties of the elementary organs, and for a more particular account of their nature and uses, see Lindley's Introduction to Botany, 2nd edit., book i.

ELEPHANT, in Latin Elephas and Elephantus; in Greek Mipaç; in Spanish Elephante; in Italian Elefante, in French Elephant; in German Olyphant; the name of the well-known genus which forms the only living type of the family of true Proboscidians or Pachydermatous Mammifers, with a proboscis and tusks, and presents the largest of existing terrestrial animals.

The proboscis or trunk, from which the name of the family is derived, demands some attention previous to our inquiry into the rest of the structure, habits, and history of the elephants.

ELENCHUS, the Latin form of the Greek elenchos The great size of the alveoli necessary for the lodgment (EXEYXos), and commonly translated by the words argumen- of the tusks renders, as Cuvier observes, the upper jaw so tum, inquisitio, confutatio, and demonstratio, is a term high and shortens the nasal bones to such a degree, that in of frequent use in the Aristotelian system of logic, and the skeleton the nostrils are placed towards the upper part signifies argument, replication, refutation, or the point, of the face; but in the living animal they are prolonged subject, or nature, of dispute or demonstration. (See the into a cylindrical trunk or proboscis composed of thouauthorities cited in Valpy's edition of Stephens's Greek sands* of small muscles variously interlaced, so as to Thesaurus under 'EXyx.) Aristotle defines elenchos as bestow on it the most complicated powers of mobility in all 'a syllogism of contradiction,' that is, an argument alleged the varieties of extension, contraction, and motion in every in opposition to another; and Mr. Thomas Taylor, in his direction. It is of a tapering subconical form, and has intranslation of the Organon, considers the Greek term to be ternally two perforations. On the upper side of the extreprecisely equivalent to Redargutio in Latin. By some of mity, immediately above the partition of the nostrils, is an the early English authors the noun elench is used in a elongated process, which may be considered as a finger; similar sense, and also the verb elenchize, meaning to argue and on the under edge is a sort of tubercle, which acts as with captious or sophistical opposition. (Johnson's Dict.) an opposable point; in short, as a thumb. Endowed with In the two last books of the Organon, entitled IIɛpi Tv exquisite sensibility, nearly 8 ft. in length, and stout in Zopiotikov 'EXkyxwv, Aristotle minutely classifies and dis- proportion to the massive size of the whole animal, this cusses the various kinds of sophistical elenchi, or modes of organ, at the volition of the elephant, will uproot trees or argument used by contentious sophists. The sophism which, gather grass-raise a piece of artillery or pick up a comfit in scholastic phraseology, is designated Ignoratio elenchi, -kill a man or brush off a fly. It conveys the food to that is, a real ignorance of, a mistaking, or sinister devia- the mouth and pumps up the enormous draughts of tion from, the argument, or question under discussion, con- water, which by its recurvature are turned into and sists in proving something irrelevant, and which, as it may driven down the capacious throat, or showered over the be true without affecting the truth of the real proposition, body. Its length supplies the place of a long neck, which with which it has no necessary connexion, does not deter- would have been incompatible with the support of the large mine, though it may seem to determine, the question. Aris-head and weighty tusks. A glance at the head of an eletotle includes under this designation the introduction of phant will show the thickness and strength of the trunk anything extraneous to the point in dispute ( Tou pay at its insertion; and the massy arched bones of the face paroc); the disproving of what is not asserted, as well as and thick muscular neck are admirably adapted for supthe proving of what is not denied. Examples of this species porting and working this powerful and wonderful instruof sophism are of very frequent occurrence in discourses ment. which display the rhetorical artifice of appealing to passions The following cuts will convey some idea of the form and and prejudices, and resort to injurious imputations, or ludi-action of the termination of the proboscis:crous and satirical illustration; especially in religious, political, and forensic disputations, which affect individual in

P C., No. 574.

Cuvier gives the number of muscles having the power of distinct action as not far short of 40,000. VOL. IX.- Y

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