Imágenes de páginas
PDF

vessel, out of which the air hath been drawn by means of the air-pump. See Pneumatics.

EXHAUSTION, in mathematics, a method in frequent use anion? the ancient mathematicians, as Euclid, Archimedes, &c, that proves the equality of two magnitudes, by a deduction ad absurdum, in supposing that, if one be greater or less than thexither, there would follow an absurdity.

This is founded upon what Euclid saith in his tenth book, era. that those quantities, whose difference is less than any assignable one, are equal. For if they were unequal, be the difference never so small, yet, it may be so multiplied, as to become greater than either of them : if not so, then it is really nothing. This he assumes in the proof of the 1st proposition of book 10, which is, that if from the greater of two quantities, you take more than its half, and from the remainder more than its half, and so continually, there will, at length, remain a quantity less than either of those proposed.

On this foundation they demonstrate, that if a regular polygon of infinite sides be inscribed in, or circumscribed about a circle; the space, that is the difference between the circle and the polygon, will, by degrees, be quite exhausted, and the circle be equal to the polygon.

EXHIBITION, a benefaction settled for the benefit of scholars in the universities, that are not on the foundation.

EXIGENT, in bar, a writ or part of the process of outlawry1 on civil actions.

EXISTENCE,'that whereby any thing has an actual essence, or is said to be. Mr. Locke says, "that we arrive at the knowledge of our own existence by intuition; of the existence of God by demonstration; and of other things by sensation. As for our own existence," continues that great philosopher, " we perceive it so plainly that it neither needs, nor is capable of any proof. I think, I reasont I feel pleasure and pain; can any of these be more evident to me than my own existence? If I doubt of all other things, that very doubt makes me perceive my own existence, and will not suffer me to doubt it. If I know I doubt, I have as certain a perception of the thing doubting, as of that thought which I call doubt: experience then convinces us that we have an intuitive knowledge of our own existence."

From the knowledge of our own existence, Mr. Locke deduces his demonstration of the existence of a God.

It has been a subject of great dispute whether external bodies have any existence but in the mind, that is, whether they really exist, or exist in idea only : the former opinion is supported by Mr. Locke, and the latter by Dr. Berkeley. " The knowledge of the existence of other things, or things without the mind, we have only by sensation: for there being no necessary connection of real existence with any idea a man hath in his memory, nor of any other existence but that of God, with the existenceof any particular man no particular man can know the existence of any other being, but only, when, by operating upon him, it makes itself be perceived by him. The having the idea of any thing in our mind no more proves the existence of that thing than the picture of a man evidences his being in the world, or the visions of a dream make u true history. It is, therefore, the actual receiving of ideas from without that gives us notice of the existence of other things, and makes us know that something does exist at that time without us which causes that idea in us, though perhaps we neither know nor consider how it does it. This notice, which we have by our senses, of the existence of things without us, though it be not altogether so certain as intuition and demonstration, yet deserves the name of knowledge, if we persuade ourselves that our faculties act and inform us right concerning the existence of those objects that affect them: but besides the assurance we have from our senses themselves, that they' do not err in the information they give us of the existence of things without us, we have other concurrent reasons; as, first, it is plain these perceptions are produced in us by external causes affecting our senses, because those that want the organs of any sense never can have the ideas belonging to that sense produced in their minds. Secondly, because we find sometimes that we cannot avoid the having those ideas produced in our minds. When my eyes are shut I can, at pleasure, recal to my mind the ideas of light, or the sun, which former sensations had lodged in my memory; but if I turn my eyes towards the sun I cannot avoid the ideas which the light or the sun then produces in me; which shews a manifest difference between those ideas laid up in the memory, and such as force themselves upon us, and we cannot avoid having; besides, there is nobody who doth not perceive the difference in himself between actually looking on the sun and contemplating the idea he has of it in his memory; and therefore he hath certain knowledge that they are not both memory or fancy. Thirdly, add to this, that many ideas are produced in us with pain, which we afterwards remember without the least offence: thus, the pain of heat or cold, when the idea of it is revived in our minds, give us no disturbance, which, when felt, was very troublesome, and we remember the pain of hunger, thirst, head-ach, &c, without any pain at all, which would either never disturb us, or else constantly do it, as often as we thought of it, were there no more but ideas floating in our minds, and appearances entertaining our fancies, without the real existence of things affecting us from abroad. Fourthly, our senses, in many cases, bear witness to the truth of each others report concerning the existence of sensible things without us: he that doubts when he sees a fire, whether it be real, may, if he pleases, feel it too, and by the exquisite pain may be convinced that it is not a bare idea, or phantom."

Dr. Berkeley, on the other hand, contends that external bodies have no existence but in the mind perceiving them, or that they exist no longer than they are perceived: his principal arguments, which several others, as well as himself, esteem a demonstration of this system, are as follow: "That neither our thoughts, passions, or ideas formed by the imagination, exist without the mind is allowed; and that the various sensations impressed on the mind, whatever objects they compose,rannot exist otherwise than in a mind perceiving them, is equally evident. This appears from the meaning of the term exist, when applied to sensible things: thus, the table I write on exists, i. e. I see and feel it; and were I out of my study I should say it existed, t. e. that were I in my study I should see and feel it as before. There was an odour, i.e. I smelt it, Sec; but the existence of unthinking beings without any relation to their being perceived is unintelligible: their esse is pcrcipi." Then to show that the notion of bodies is grounded on the doctrine of abstract ideas," What," he asks," are light and colours, heat and cold, extension and figure, in a word, the tilings we see and feel, but so many sensations, notions, ideas, or impressions on the sense; and is it possible to separate, even in thought, any of these from perception? The several bodies then that compose the frame of the world have not any subsistence without it mind: their

esse is to be perceived or known; and if they are not perceived by me, nor by any other thinking being, they have no shadow of existence at all: the things we perceive are colour, figure, motion, Sec. that is, the ideas of those things; but has an idea any existence out of the mind? To have an idea is the same thing as to perceive , that, therefore, wherein colour, figure, &c. exist, must perceive them. "It is evident, therefore, that there can be no unthinking substance, or substratum of those ideas. But you may argue, if the ideas themselves do not exist without the mind, there may be things like them, whereof they are copies or resemblances, which exist without the mind. It is answered, an idea can be like nothing but an idea, a colour or figure can be nothing else but another colour or figure. It may be further asked, whether those supposed original or external things, whereof our ideas are the pictures, be themselves perceivable or not? If they be not, I appeal to any one whether it be sense to say a colour is like somewhat which is invisible, hard or soft, like somewhat (intangible, &c. Some distinguish between primary and secondary qualities, the former, tir. extension, solidity, figure, motion, rest, and number, have a real existence out of the mind'; for the latter, under which come all other sensible qualities, as colours, sounds, tastes, &c. they allow the ideas we have of them are not resemblances of any tiling without the mind, or unperceived, but depend on the size, texture, motion, &c, of the minute particles of matter. Now it is certain that those primary qualities are inseparably united with the other secondary ones, and cannot even in thought be abstracted from them, and therefore must only exist in the mind. Again, great or small, swift or slow, are allowed to exist no where without the mind, being merely relative, and changing as the frame or position of the organ changes: the extension, therefore, that exists without the mind is neither great nor small, the motion neither swift nor slow, i.e. they are nothing. That number is a creature of the mind is plain, (even though the other qualities were allowed to exist) from this, that the same thing bears a different denomination of number as the mind views it with different respects: thus, the same extension is 1,3, or 36, as the mind considers it, with reference to a yard, a foot, or an inch.

"In effect, after the same manner, as the modern philosophers prove colours, tastes &c. to liave no existence in matter, or without the mind, the same thing may be proved of all sensible qualities whatever: thus, they say, heat and cold are only the affections of the mind, not at all patterns of real beings existing in corporeal substances, for that the same body which seems cold to one band seems warm to another. Now, why may we not as well argue that figure and extension are not patterns or resemblances of qualities existing in matter, because, to the same eye, at different stations, or to eyes of different structure, at the same station, they appear various? Again, sweetness, it is proved, does not exist in the thing sapid, because the thing remaining unaltered, the sweetness is changed to bitterness, as in a fever, or by any otherwise vitiated palate. Is it not as reasonable to say that motion does not exist out of the mind, since if the succession of ideas in toe mind become sinister, the motion, it is acknowledged, will appear slower, without any external alteration? Ap;ain, were it possible for solid figured bodies to exist out of the mind, yet it were impossible for us ever to know it: our senses, indeed, give us sensations of ideas, but do not tell us that any tiling exists without the mind, or unperceived, like those, which are perceived; this the materialists allow. No other way therefore remains, but that we know them by reason's inferring their existence from what is immediately perceived by sense; but how should reason do this, when it is confessed there is not any necessary connection between our sensations and these bodies? It is evident, from the phenomena of dreams, pltrensies, &c. that we may be affected with the ideas we now have, though there were no bodies existing without them; nor does the supposition of external bodies at all forward us in conceiving how our ideas should come-to be produced."

EXOACANTHA, in botany, a genus of the Pentandria Digynia class and order. Natural order of Umbellatse. Essential character: involute spiny; involucle halved, with unequal rays; flowers all hermaphrodite, with equal, index, heart-shaped petals; seeds ovate, striate. There is but one species, viz. E. heterophylla, found by Billardiere near Nazareth.

EXOCXETUS, the flying fish, in natural history, a genus of fishes of the order A bdominales. Generic character: head scaly; mouth without teeth; jaws connected on each side; gill membrane, ten rayed; pec

VOL. III.

toral fins very long and large, and giving, to a certain degree, the power of flight. There are three species. We shall particularly notice the E. exilien, or the Mediterranean flyi '-fish. This is about* fourteen inches in length, and is found principally in the Mediterranean and Atlantic Seas, frequently alone, and sometimes in small companies. By the extraordinary length of its pectoral fins it is enabled to quit the water and support a flight, about three feet above the surface,-for the distance of eighty or a hundred yards, after which it is obliged to return to the water and moisten its fins, which, even in this short progress, become hard and dry. These fishes are persecuted by the dorado under the water, and by the gull, or albatross, above the surface of it, and thus often escape destruction by the one only to incur it from the other. This faculty of maintaining short frights in the air is possessed by several other fishes, particularly by the scorpxna and the trigla. The air-bladder of the flying-fish is extremely large, and, of consequence, highly assisting to its aerial progress. The roe of tliis fish is reported to be highly caustic; the smallest quantity applied to the tongue producing some degree of excoriation. For a representation of the oceanic flying-fish, see Pisces, Plate IV, fig. 2.

EXORDIUM, in rhetoric, is the, preamble or beginning, serving to prepare the audience for the rest of the discourse. Exordiums are of two kinds, either just and formal, or vel:em(r.it and abrupt. Tie last are most suitable on occasions of extraordinary joy, indignation, or the like. All exordiums should be composed with a view to captivate the good will, or attract the attention of the audience. The first may be done by paying them some compliment: thus St. Paul, " I think myself happy, king Agrippa, because I shall answer for myself this day before thee, touching all the things whereof I am accused with the Jews, especially because I know thee to be expert in all customs and questions which are among the Jews."

The requisites in an exordium are, 1. Propriety, whereby it becomes of a piece with the subject, and matches it as a part does a whole: in this the Greeks were very defective. 2. Modesty, which very much recommends the orator to the favour of his audience. And, 3. Brevity, not amplified or swelled with a detail of circumstances.

EXOTERIC, and EsoTumc, terms denoting external and internal, and applied H

to the double doctrine of the ancient philosophers: the one was public or exoteric, the other secret or esoteric. The first was that which they taught openly to the world, the latter was confined to a small number of disciples. See Peripatetics.

EXOTIC, an appellation denoting a thing to be the produce of foreign countries. Exotic plants of the hot climates are very numerous, and require the utmost attention of the gardener to make them thrive with us.

EXPANSION, in natural philosophy, the enlargement or increase of bulk in bodies, chiefly by means of heat. This is one of the most general effects of caloric, being common to all bodies whatever, whether solid or fluid, or in an aeriform state. In some cases bodies seem to expand as they grow cold, as water in the act of freezing; this, however, is known to be no exception to the general rule, but is owing to the arrangement of the particles, or to crystallization, and is not a regular and gradual expansion like that of metals, or other solid substances by means of heat. In various metals likewise an expansion takes place in passing from a fluid to a solid state, which is accounted for in the same way. The expansion of solids is exhibited by the PyroMeter (which see); a rod of iron, for instance, becomes sensibly longer and larger in all its dimensions in passing from a low to a high state of temperature. The expansion of fluids is shewn by the thermometer, and is the principle upon v. fi.ch that useful instrument is constructed, by immersing a thermometer into hot water, the mercury, or other fluid, contained in it immediately expands. See Thermometer. The degree of expansion produced in different liquids, varies very considerably. In general, the denser the fluid, the less the expansion; water expands more than mercury, and alcohol, which is lighter than water, expands more than water. The expansion of aeriform fluids may be exhibited by bringing it bladder, partly filled with air, and the neck closely tied, near the fire; the bladder will soon be distended, and will, if the heat he strong enough, burst. Metal* expand in the following order, those that expand mot arc placed first: zinc, lead, tin, copper, bismuth, iron, platina.

EXPECTATION of life, a term used by the writers on life annuities and reversions, and which, according to Dr. Price, signifies the mean continuance of any given single, joint, or surviving lives, according to any

given table of observations: that is, the number of years which, taking them one with another, they actually enjoy, and may be considered as sure of' enjoying; those who live or survive beyond that period, enjoying as much more time, in proportion to their number, as those who fall short of it enjoy less. See Life, duration of.

EXPECTORANTS, an appellation given to those medicines which facilitate the discharging the contents of the lungs.

EXPECTORATION, the act of evacuating or bringing up phlegm, or other matters out of the trachea, lungs, &c, by coughing, hauking, spitting, &c.

EXPEDITION, in military affairs, is chiefly used to denote a voyage or march against an enemy, the success of which depends on rapid and unexpected movements. No rules have, or probably can be given for the application of expeditions generally; they depend on circumstances that cannot be foreseen; they seem to depend on the following maxims: 1. Secresy of preparation and concealment of design. 2. The means must 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 phenomena 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 inquiries 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 reasoning; and these rules of philosophizing 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 phenomena; 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, a* 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 intertise, 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 experimenttl philosophy, propositions collected from the phenomena by induction, are to be deemed (notwithstanding contrary hypotheses) either exactly or very nearly true, till other phenomena occur, by which they may be rendered either more accurate, or liable to exceptions. This ought to be done, lest arguments of induction should be destroyed by hypothesis.

These four rules of philosophizing 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 proceeding 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 demon stration 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 phenomena, the conclusion maybe 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 motions 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 analysis. And that of synthesis, or composition, consists in assuming causes, discovered and established as principles, and by them explaining the phenomena, proceeding from them, and proving the explanations.'' See Acoustics, Aerostation, Electricity, HydrostaTics, Magnetism, Mechanics, Optics, Pneumatics, &C. &C.

EXPERIMENTUM cruris, 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, at it were, extorted by force.

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

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 iu 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, a* H t

« AnteriorContinuar »