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be proportional to the end. 3. There must be an accurate knowledge of the state and situation of the country. 4. The plan must be well arranged, and the commander perfectly adapted to the particular sort of business.

EXPERIENCE, a kind of knowledge acquired by long use, without any teacher. Mr. Locke says that men receive all the materials of knowledge from experience and observation. Experience then consists in the ideas of things we have seen or read, which the judgment has reflected on, to form itself a rule or method.

EXPERIMENTAL philosophy, that philosophy which proceeds on experiments,

which deduces the laws of nature, and

the properties and powers of bodies, and their actions upon each other, from sensible experiments and observations. The business of experimental philosophy is to inquire into and to investigate the reasons and causes of the various appearances or phænomena of nature, and to make the truth or probability thereof obvious and evident to the senses, by plain, undeniable, and adequate experiments, representing the several parts of the grand machinery and agency of nature.

In our inquries into nature, we are to be conducted by those rules and maxims which are found to be genuine, and consonant to a just method of physical rea soning; and these rules of philosophising are, by the greatest master in science, Sir Isaac Newton, reckoned four, which are as follows:

1. More causes of natural things are not to be admitted, than are both true, and sufficient to explain the phænomena; for nature does nothing in vain, but is simple, and delights not in superfluous causes of things.

2. And, therefore, of natural effects of the same kind, the same causes are to be assigned, as far as it can be done; as of respiration in man and beasts, of the descent of stones in Europe and America, of light in a culinary fire and in the sun, and of the reflection of light in the earth and in the planets.

3. The qualities of natural bodies which cannot be increased or diminished, and agree to all bodies in which experiments can be made, are to be reckoned as the qualities of all bodies whatsoever: thus, because extension, divisibility, hardness, impenetrability, mobility, the vis inertiæ, and gravity, are found in all bodies which fall under our cognizance or inspection, we may justly conclude they

belong to all bodies whatsoever, and are therefore to be esteemed the original and universal properties of all natural bodies.

4. In experimental philosophy, propositions collected from the phænomena by induction are to be deemed (notwithstanding contrary hypotheses) either exactly or very nearly true, till other phænomena occur, by which they may be rendered either more accurate, or liable to exception. This ought to be done, lest arguments of induction should be destroyed by hypothesis.

These four rules of philosophising are premised by Sir Isaac Newton to his third book of the "Principia;" and more particularly explained by him in his " Optics," where he exhibits the method of proceed. ing in philosophy, the first part of which is as follows:

"As in mathematics, so in natural history, the investigation of difficult things, by way of analysis, ought always to precede the method of composition. This analysis consists in making experiments and observations, and in drawing general conclusions from them by induction, (i. e. reasoning from the analogy of things by natural consequence) and admitting no objections against the conclusions but what are taken from experiments or certain truths. And although the arguing from experiments and observation, by induction, be no demonstration of general conclusions, yet it is the best way of arguing which the nature of things admits of, and may be looked on as so much the stronger, by how much the induction is more general; and if no exception occur from phænomena, the conclusion may be pronounced generally: but if, at any time afterwards, any exception shall occur from experiments, it may then be pronounced with such exceptions: by this way of analysis we may proceed from compounds to ingredients, and from mo tions to the causes producing them; and, in general from effects to their causes; and from particular causes to more general ones, till the argument ends in the most general: this is the method of anaIvsis. And that of synthesis, or composition, consists in assuming causes, discovered and established as principles, and by them explaining the phænomena proceeding from them, and proving the explanations." See ACOUSTICS, ALROSTATION, ELECTRIcity, HydrostATICS, MAGNETISM, MECHANICS, OPTICS, PNEUMATICS, &c. &c.

EXP

EXPERIMENTUM crucis, a capital, leading, or decisive experiment; thus termed, either on account of its being like a cross or direction post, placed in the meeting of several roads, guiding men to the true knowledge of the nature of that thing they are inquiring after; or, on account of its being a kind of torture, whereby the nature of the thing is, as it were, extorted by force.

EXPIRATION, in physic, that part of respiration, whereby the air is expelled or driven out of the lungs. See Pur

SIOLOGY.

EXPLOSION, in natural philosophy, a sudden and violent expansion of an aerial or other elastic fluid, by which it instantly throws off any obstacle that happens to be in the way, sometimes with incredible force, and in such a manner as to produce the most astonishing effects. It differs from expansion in this, that the latter is a gradual and continued power, acting uniformly for some time; whereas the former is always sudden, and only of momentary duration. The expansions of solid bodies do not terminate in violent explosions, on account of their slowness, and the small space through which the metal, or other expanding substance, moves. Thus wedges of dry wood driven into stone, and wetted, will cleave the most solid blocks, but they never throw the parts to any distance, as is the case with gunpowder; but the expansion of elastic fluids will burst solid substances, and throw the fragments a great way off: for this two reasons have been assigned: 1. The immense velocity with which aerial fluids expand, when suddenly affected with high degrees of heat: and 2. The great celerity with which they acquire heat, and are affected by it. an example, air, when heated as much as iron, when brought to a white heat, is expanded to four times its bulk; but the metal itself will not be expanded the 500th part of the space. In the case of gunpowder, which is well known as an explosive substance, the velocity with which the flame moves is estimated at 7000 feet in a second. Hence the impulse of the fluid is inconceivably great, and the obstacles on which it strikes are hurried off with vast velocity, viz. at the rate of 27 miles per minute. The velocity of the bullet is also promoted by the sudden propagation of the heat through the whole body of air, as soon as it is extricated from the materials of which the gunpowder is made, so that it strikes at

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once. Hence it has been inferred, that explosion depends first on the quantity of elastic fluid to be expanded: secondly, on the velocity it acquires by a certain degree of heat: and, thirdly, on the celerity with which the degree of heat affects the whole expansive fluid.

EXPONENT, in algebra, is a number placed over any power, or involved quantity, to shew to what height the root is raised: thus, 2 is the exponent of x2, and The 4 the exponent of x4, or xxxx. rule for dividing powers of the same quanty is, to substract the exponents, and make the difference the exponent of the quotient: if, therefore, a lesser power is divided by a greater, the exponent of the quotient must, by this rule, be negative : =a4—6—a—2.

thus,

a4

a4

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and hence is expressed by a2, with a negative exponent. It is also obvious, that =1, and there

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quantities, a, 1.
be expressed thus, a1, a°, u—13, a—2, a—3,
a-, &c. These are called the negative
powers of a, which have negative expo-
nents; but they are at the same time po-
sitive powers of

1

--, or a

a

EXPONENT of a ratio, is the quotient arising from the division of the antecedent by the consequent: thus, in the ra

tio of 5 to 4, the exponent is 14; but the exponent of 4: 5, is. If the consequent be unity, the antecedent itself is the exponent of the ratio: thus the exponent of the ratio 4: 1 is 4. Wherefore the exponent of a ratio is to unity as the antecedent is to the consequent. Although the quotient of the division of the antecedent by the consequent is usually taken for the exponent of a ratio, yet in reality the exponent of a ratio ought to be a logarithm. And this seems to be more agreeable to Euclid's definition of duplicate and triplicate ratios, in his fifth book. For 1, 3, 9, are continual proportionals; now if be the exponent of the ratio of 1 to 3, and or 98 exponent of the ratio of 3 to 9; and the exponent of the ra

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tio of 1 to 9; and since, according to Euclid, if three quantities be proportional, the ratio of the first to the third is said to be the duplicate of the ratio of the first to the second, and of the second to the third; therefore, according to this, must be the double of, which is very false. But it is well known, the logarithm of the ratio of 1 to 9, that is, the logarithm of 9, is the double of the ratio of 1 to 3, or 3 to 9, that is, the logarithm of 3. From whence it appears that logarithms are more properly the exponents of ratios, than numerical quotients; and Dr. Halley, Mr. Cotes, and others, are of the same opinion.

EXPONENT, is also used in arithmetic, in the same sense as index or loga

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24 +0.1.2.3.4.5 EXPONENTIAL equation, is that wherein there is an exponential quantity. See the next article.

EXPONENTIAL quantity, is a quantity whose power is a variable quantity, as xx, ax. Exponential quantities are of several degrees and orders, according as the exponents themselves are more or less involved. If the exponent be a simple quantity, as zy, it is called an exponenual of the first or lowest degree; but when the exponent itself is an exponential of the first degree, as zy, it is called an exponential of the second degree. In like manner, if the exponent itself be an exponential of the second degree, as xy, it is called an exponential of the third degree, &c.

EXPORTATION, the act of sending goods out of one country into another. In modern times it has been the principal object of commercial policy, in almost every country, to encourage exportation, except with respect to a few particular articles; the export of manufactured goods has been promoted, with a view of encouraging the internal industry of the country, and the export of foreign produce, as a means of drawing wealth from other countries by the profits of the carrying trade. The excess of the value of goods exported, beyond that of the im

ports has usually been considered as a criterion of the profits which a country derives from foreign trade; but this is a very fallacious mode of determining a point of great importance; advantageous foreign trade might long exist, even if the imports constantly exceeded the value of the exports. The laws in force relating to exportation, consist principally of prohibitory or restrictive regulations, respecting bullion, corn, wool, machinery, and tools used in various branches of manufactures, the exportation of which, it is thought, might diminish the necessary supply of provisions for the consump tion of the country, or enable foreigners to rival valuable branches of its manu

factures. The acts relative to the exportation of wool prohibit the exportation, not only of the article itself, but also of live sheep, rams, or lambs, from Great Britain, Ireland, Jersey, Guernsey, Alderney, Sark, or Man, on penalty of the forfeiture thereof, and of the ships conveying the same; also 31. for every sheep,

&c. and the offender to suffer three months solitary imprisonment; for a second offence 51. per sheep, &c. and six months imprisonment; except wether sheep for ships' use only, put on board by licence of the port officer of the cus. toms. A limited quantity of wool is, however, permitted to be exported from the port of Southampton to Jersey, Guernsey, Alderney, and Sark. The duties on exportation, payable in Great Britain and Ireland, which were formerly the principal branch of the revenue derived from foreign trade, are now of small amount, in comparison with the duties payable on goods brought into the country. See CUSTOMS.

EXPRESSED oil. See OIL.

EXPRESSION, in chemistry, or pharmacy, denotes the act of expressing out the juices or oils of vegetables, which is one of the three ways of obtaining them; the other two being by infusion and decoction. The hard fruits require to be well bruised previously to expression, but herbs are only to be moderately bruised. They are then to be included in a hair bag, and pressed between wooden plates in the common screw press, till the juice ceases to run. The expression of oils is performed nearly in the same manner as that of juices, only iron plates are to be used instead of wooden ones. The insipid oils of all unctuous seeds are obtained uninjured by this operation, if performed without the aid of heat, which

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though it promotes the extraction of the oil, gives it an ungrateful flavour. The oils expressed from aromatic substances generally carry with them a portion of their essential oil. Hence the smell and flavour of the expressed oils of nutmegs

and mace.

EXPRESSION, in rhetoric, the elocution, diction, or choice of words in a discourse. Beautiful expression is the natural and true light of our thoughts: it is to this we owe all the excellencies in discourse, which gives a kind of vocal life and spirit. As the principal end of discourse is to be understood, the first thing we should endeavour to obtain is a richness of expression, or habit of speaking so well, as to make our thoughts easily understood.

EXPRESSION, in painting, a natural and lively representation of the subject, or of the several objects intended to be shewn. The expression consists chiefly in representing the human body, and all its parts, in the action suitable to it: in exhibiting in the face the several passions proper to the figures, and observing the motions they impress on the external parts. See PAINTING.

EXSICCATION, in pharmacy, the drying of moist bodies, for which two methods are usually employed; in one the humid parts are exhaled by heat, in the other they are imbibed or absorbed by substances, whose texture is adapted to the purpose. Bodies combined with, or dissolved in a fluid, require the first: such as are only superficially mixed with it, are separated by the second method. Vegetables are usually exsiccated by the natural warmth of the air, but the assistance of a gentle artificial heat is often found very useful. By a moderate fire the more tender flowers may be dried in a short time, without any considerable loss either of their odour or lively colour, which would be injured, or perhaps destroyed, by the more slow exsiccation in the air. Some plants, particularly those of the acrid kind, lose their virtues by

that process.

EXTENSION, in philosophy, one of the common and essential properties of body, or that by which it possesses or takes up some part of universal space, which is called the place of that body.

Extension is divided, 1. Either into length only, and then it is called a line; or, 2. Into length and breadth, which is called a superficies; or, 3. Into length, breadth, and depth, which is called a solid; being the three dimensions according to the quantity of which the magniVOL. V.

tude or bulk of bodies are estimated. Extension, according to Mr. Locke, is space considered between the extremities of matter, which fills up its capacity with something solid, tangible, and moveable. Space, says that philosopher, may be conceived without the idea of extension, which belongs to body only.

EXTENSOR, an appellation given to several muscles, from their extending or stretching the parts to which they belong. See ANATOMY.

EXTENT, in law, a writ of execution or commission to the sheriff, of one who, being bound by statute, has forfeited his bond, for the valuing of lands or tenements; sometimes the act of the sheriff upon this writ.

EXTERMINATION, in general, the extirpating or destroying something. In algebra, surds, fractions, and unknown quantities, are exterminated by rules for reducing equations. Thus to take away the frac

tional form from these equations

so

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b y

=; in both cases we multiply

y

and
2c
the numerator of one fraction by the de-
nominator of the other, and the equations
· bx and a1y+b2y = 2 cx:
become a y =
again, to take away the sign of the
square, or cube, or other root, as2/a2+y'
4z, we raise the 4 z to the second pow-
er, and take off the sign of the root on
the other side of the equation thus, a'+y*
=16z: and when n✅a+6=x: then
a+b=xn. To exterminate a quantity
from any equation there are divers rules.
See ALGEBRA.

We shall however give an instance in
this place: thus to exterminate y out of
3b=2x+y
these two equations a+b+y

subtract the upper equation from the un-
b-a
der and there remains 36-a-x-2x-b,
hence 3x=4b—a and 4—1′

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same manner.

EXTERNAL medicines, the same with local or topical medicines.

EXTERNAL angles, are the angles on the outside of any right-lined figure, when all the sides are severally produced, and they are all, taken together, equal to four right angles.

EXTINGUISHMENT, in law, whereever a right, title, or interest is destroyed, or taken away by the act of God, operation of law, or act of the party, it is called an extinguishment; a creditor's accepting a higher security than he had before is an extinguishment of the first debt.

EXTORTION, in law, any oppression by colour or pretence of right.

EXTRA judicial, in law, is when judgment is given in a cause or case not depending in that court, where such judg ment is given, or wherein the judge has no jurisdiction.

EXTRA parochial, out of any parish; privileged or exempted from the duties of a parish.

EXTRACT, in pharmacy, the soluble parts of vegetable substances, first dissolved in spirit or water, and then reduced to the consistence of a thick syrup or paste, by evaporation. PHARMACY.

See

EXTRACTION, in chemistry, is the general operation, by means of which we separate and extract from very compounded bodies of the vegetable and animal kingdoms, different matters contained in them. For this purpose alcohol, water, acids, and alkalies, are made use of. Therefore extraction is performed by dissolutions, macerations, infusions, &C.

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EXTRACTOR, in midwifery, an instrument or forceps, for extracting children by the head. See MIDWIFERY,

EXTRAVASATION, in contusions, fissures, depressions, fractures, and other accidents of the crauium, is when one or more of the blood-vessels that are distributed on the dura mater is broke or di vided, whereby there is such a discharge of blood as greatly oppresses the brain, and disturbs its offices; frequently bringing on violent pains, and other mischiefs; and, at length, death itself, unless the patient is timely relieved.

EXTREME and mean proportion, in geometry, is when a line is so divided into two parts, that the rectangle under the whole line, and the lesser segment, is equal to the square of the greater seg. ment.

EXUVIÆ, among naturalists, denote the cast-off parts or coverings of animals, as the skins of serpents, caterpillars, and other insects. See ENTOMOLOGY.

M. Reaumur is very particular in describing the manner in which the caterpillar tribe throw off, or extricate themselves from their exuviæ. See vol. i. of the "History of Insects."

The crab, some spiders and phalangii, as is well known, can even throw off their limbs at pleasure, which are again replaced by new ones. See CANCER.

EXUVIE is also used for the remains of sea animals, found fossile, and more properly called extraneous, or marine fossils. EYE. See ANATOMY and OPTICS.

EYE, in architecture, is used to signify any round window made in a pediment, an attic, the reins of a vault, or the like.

EYE of a dome, an aperture at the top of a dome, as that of the Pantheon at Rome, or of St. Paul's at London: it is usually covered with a lantern.

EYE, in agriculture and gardening, sig. nifies a little bud, or shoot, inserted into a tree, by way of graft.

EYE of a tree, a small pointed knot to which the leaves stick, and from which the shoots or sprigs proceed.

Ex-bright. See EUPHRASIA.

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