By whose direction is the nutriment so regularly distributed into the respective parts, and how are they kept to their specifick uniformities? Glanville. He intendeth the care of species or common natures, but letteth loose the guard of individuals or single existencies. Browne.

Thou nam'st a race which must proceed from me, Yet my whole species in myself I see. Dryden.

It is a most certain rule, how much any body hath of colour, so much hath it of opacity, and by so much the more unfit it is to transmit the species. Ray on the Creation.

Human reason doth not only gradually, but specifically, differ from the fantastick reason of brutes, which have no conceit of truth, as an aggregate of divers simple conceits, nor of any other universal.

Grew.

As all things were formed according to these specifical platforms, so their truth must be measured from their conformity to them.

Norris.

Though our charity should be universal, yet, as it cannot be actually exercised but on particular times, so it should be chiefly on special opportunities. Sprat's Sermons.

St. Peter doth not specify what these waters were. Burnet.

The understanding, as to the exercise of this power, is subject to the command of the will, though, as to the specifick nature of its acts, it is determined by the object. South.

His faith must be not only living, but lively too; it must be put into a posture by a particular exercise of those several virtues that are specifically requisite to a due performance of this duty. ld. Sermons. Milton's subject was still greater than Homer's or Virgil's; it does not determine the fate of single persons or nations, but of a whole species. Addison.

The constitution here speaks generally, without the specification of any place. Ayliffe's Parergon. Specifick gravity is the appropriate and peculiar gravity or weight which any species of natural bodies have, and by which they are plainly distinguishable from all other bodies of different kinds.

Quincy.

The species of the letters illuminated with blue, were nearer to the lens than those illuminated with deep red, by about three inches, or three and a quarter; but the species of the letters illuminated with indigo and violet appeared so confused and indistinct, that I could not read them. Newton's Opticks. These principles I consider not as occult qualities, supposed to result from the specifick forms of things, but as general laws of nature, by which the things themselves are formed; their truth appearing to us by phænomena, though their causes be not yet discovered.

Id.

He cannot but confess that it is a thing the most desirable to man, and most agreeable to the goodness of God, that he should send forth his light and his truth by a special revelation of his will. Rogers.

Our Saviour is represented every where in scripture as the special patron of the poor and the afflicted, and as laying their interest to heart more nearly than those of any other of his members. Atterbury.

As there was in the splendour of the Roman empire, a less quantity of current species in Europe than there is now, Rome possessed a much greater proportion of the circulating species of its time than any European city.

Arbuthnot.

The specifick qualities of plants reside in their native spirit, oil, and essential salt: for the water, fixt salt, and earth, appear to be the same in all plants. A mind of superior or meaner capacities than human, would constitute a different species, though

Id.

united to a human body in the same laws of connexion and a mind of human capacities would make another species, if united to a different body in different laws of connexion. Bentley's Sermons.

He must allow that bodies were endowed with the same affections then as ever since; and that, if an axe-head be supposed to float upon water, which is specifically lighter, it had been supernatural.

Bentley.

If she would drink a good decoction of sarsa, with the usual specificks, she might enjoy a good health. Wiseman.

A special idea is called by the schools a species. Watts.

Specifick difference is that primary attribute which distinguishes each species from one another, while they stand ranked under the same general nature or genus. Though wine differs from other liquids, in that it is the juice of a certain fruit, yet this is but a general or generick difference? for it does not distinguish wine from cyder or perry: the specifick difference of wine therefore is its pressure from the grape; as cyder is pressed from apples, and perry from pears. Id.

This specification or limitation of the question hinders the disputers from wandering away from the precise point of enquiry.

Id.

He has there given us an exact geography of Greece, where the countries, and the uses of their soils are specified. Pope.

SPECIALTY, specialitas, in English law, a bond, bill, or such like instrument: a writing or deed, under the hand and seal of the parties.Littleton. These are looked upon as the next class of debts after those of record; being confirmed by special evidence under seal. 2 Comm. c. 30, p. 465.

SPECIES, in algebra, are the letters, symbols, marks, or characters, which represent the quantities in any operation or equation.

SPECIES, in commerce, the several pieces of gold, silver, copper, &c., which, having passed their full preparation and coinage, are current in public. See MONEY.

SPECIES, in logic, a relative term, expressing an idea which is comprised under some general one called a genus. See LOGIC.

SPECIES, in optics, the image painted on the retina by the rays of light reflected from the several points of the surface of an object, received in by the pupil, and collected in their passage through the crystalline, &c.

SPECIFIC, in philosophy, that which is peculiar to any thing, and distinguishes it from all others.

SPECIFIC DIFFERENCES OF PLANTS. See BoTANY, Index.

SPECIFIC GRAVITY is a term much employed in the discussions of modern physics. It expresses the weight of any particular kind of matter, as compared with the weight of the same bulk of some other body of which the weight is supposed to be familiarly known, and is therefore taken for the standard of comparison. body generally made use of for this purpose is pure water. See HYDROSTATICS.

The

The specific gravity of bodies is a very interesting question both to the philosopher and to the man of business. The philosopher considers the weights of bodies as measures of the number of material atoms, or the quantity of matter

which they contain. This he does on the supposition that every atom of matter is of the same weight, whatever may be its sensible form. This supposition, however, is made by him with caution, and he has recourse to specific gravity for ascertaining its truth in various ways. The man of business entertains no doubt of the matter, and proceeds on it as a sure guide in his most interesting transactions. We measure commodities of various kinds by tons, pounds, and ounces in the same manner as we measure them by yards, feet, and inches, or by bushels, gallons, and pints; nay, we do this with much greater confidence, and prefer this measurement to all others whenever we are much interested to know the exact proportions of matter that bodies contain. The weight of a quantity of grain is allowed to inform us much more exactly of its real quantity of useful matter than the most accurate measure of its bulk. We see many circumstances which can vary the bulk of a quantity of matter, and these are frequently such as we cannot regulate or prevent; but we know very few that can make any sensible change in this weight without the addition or abstraction of other matter. Even taking it to the summit of a high mountain, or from the equator to the polar region, will make no change in its weight as it is ascertained by the balance, because there is the same real diminution of weight in the pounds and ounces used in the examination. Notwithstanding the unavoidable change which heat and cold make in the bulk of bodies, and the permanent varieties of the same kind of matter which are caused by different circumstances of growth, texture, &c., most kinds of matter have a certain consistency in the density of their particles, and therefore in the weight of a given bulk. Thus the purity of gold, and its degree of adulteration, may be inferred from its weight, it being purer in proportion as it is more dense. The density, therefore, of different kinds of tangible matter becomes characteristic of the kind, and a test of its purity; it marks a particular appearance in which matter exists, and may therefore be called, with propriety, specific. But this density cannot be directly observed. It is not by comparing the distances between the atoms of matter in gold and in water that we say the first is nineteen times denser than the last, and that an inch of gold contains nineteen times as many material atoms as an inch of water; we reckon on the equal gravitation of every atom of matter, whether of gold or of water; therefore the weight of any body becomes the indication of its material density, and the weight of a given bulk becomes specific of that kind of matter, marking its kind, and even ascertaining its purity in this form. To make this comparison of general use, the standard must be familiarly known, and must be very uniform in its density, and the comparison of bulk and density must be easy and accurate. The most obvious method would be to form, with all nicety, a piece of the standard matter of some convenient bulk, and to weigh it very exactly, and keep a note of its weight: then, to make the comparison of any other substance, it must be made into a mass of the same precise bulk, and weighed with equal care; and the most convenient way of expressing the specific gravity would be to consider the

weight of the standard as unity, and then the number expressing the specific gravity is the number of times that the weight of the standard is contained in that of the other substance. This comparison is most easily and accurately made in fluids. We have only to make a vessel of known dimensions equal to that of the standard which we employ, and to weigh it when empty, and then when filled with the fluid. Nay, the most diff cult part of the process, the making a vessel of the precise dimensions of the standard, may be avoided, by using some fluid substance for a standard. Any vessel will then do; and we may ensure very great accuracy by using a vessel with a slender neck, such as a phial or matrass; for, when this is filled to a certain mark in the neck, any error in the estimation by the eye will bear a very small proportion to the whole. The weight of the standard fluid, which fills it to this mark being carefully ascertained, is kept in remembrance. The specific gravity of any other fluid is had by weighing the contents of this vessel when filled with it, and dividing the weight by the weight of the standard. The quotient is the specific gravity of the fluid. But in all other cases this is a very difficult problem: it requires very nice hands, and an accurate eye, to make two bodies of the same bulk. An error of th part in the linear dimensions of a solid body makes an error of one-thirtieth part in its bulk; and bodies of irregular shapes and friable substance, such as the ores of metals, cannot be brought into convenient and exact dimensions for measurement. From all these inconveniences and difficulties we are freed by the celebrated Archimedes, who, from the principles of hydrostatics discovered or established by him, deduced the accurate and easy method which is now universally practised for discovering the specific gravity and density of bodies. See ARCHIMEDES. Instead of measuring the bulk of the body by that of the displaced fluid (which would have been impossible for Archimedes to do with any thing like the necessary precision), we have only to observe the loss of weight sustained by the solid. This can be done with great ease and exactness. Whatever may be the bulk of the body, this loss of weight is the weight of an equal bulk of the fluid; and we obtain the specific gravity of the body by simply dividing its whole weight by the weight lost: the quotient is the specific gravity when this fluid is taken for the standard, even though we should not know the absolute weight of any given bulk of this standard. It also gives us an easy and accurate method of ascertaining even this fundamental point. We have only to form any solid body into an exact cube, sphere, or prism, or known dimensions, and observe what weight it loses when immersed in this standard fluid. This is the weight of the same bulk of the standard to be kept in remembrance; and thus we obtain, by the by, a most easy and accurate method for measuring the bulk or solid contents of any body, however irregular its shape may be. We have only to see how much weight it loses in the standard fluid; we can compute what quantity of the standard fluid will have this weight. Thus should we find that a quantity of sand, or a furze bush, loses 250 ozs.,

when immersed in pure water, we learn by this that the solid measure of every grain of the sand, or of every twig and prickle of the furze, when added into one sum, amounts to the fourth part of a cubic foot, or to 432 cubic inches.

To all these advantages of the Archimedean method of ascertaining the specific gravity of bodies, derived from his hydrostatical doctrines and discoveries, we may add, that the immediate standard of comparison, namely, water, is, of all the substances that we know,, the fittest for the purpose of a universal standard of reference. In its ordinary natural state it is sufficiently constant and uniform in its weight for every examination where the utmost mathematical accuracy is not wanted; all its variations arise from impurities, from which it may at all times be separated by the simple process of distillation: and we have every reason to think that, when pure, its density, when of the same temperature, is invariable. Water is therefore universally taken for the unit of that scale on which we measure the specific gravity of bodies, and its weight is called 1. The specific gravity of any other body is the real weight in pounds and ounces, when of the bulk of one pound or one ounce of water. It is, therefore, of the first importance, in all discussions respecting the specific gravity of bodies, to have the precise weight of some known bulk of pure water. For this purpose we shall reduce all to the English cubic foot and avoirdupois ounce of the exchequer standard, on account of a very convenient circumstance peculiar to this unit, viz. that a cubic foot contains almost precisely 1000 ozs. of pure water, so that the specific gravity of bodies expresses the number of such ounces contained in a cubic foot. We begin with a trial made before the house of commons in 1696 by Mr. Everard. He weighed 2145-6 cubic inches of water by a balance, which turned sensibly with six grains, when there were thirty pounds in each scale. The weights employed were the troy weights, in the deposit of the court of exchequer, which are still preserved, and have been most scrupulously examined and compared with each other. The weight was 1131 ozs. fourteen pennyweights. This wants just eleven grains of 1000 avoirdupois ounces for 1728 cubic inches, or a cubic foot; and it would have amounted to that weight had it been a degree or two colder. The temperature indeed is not mentioned; but, as the trial was made in a comfortable room, we may presume the temperature to have been about 55° of Fahrenheit's thermometer. The dimensions of the vessel were as accurate as the nice hand of Mr. Abraham Sharp, Mr. Flamsteed's assistant at Greenwich, could execute, and it was made by the exchequer standard of length. This is confided in by the naturalists of Europe, as a very accurate standard experiment, and is confirmed by many others, both private and public. The standards of weight and capacity employed in the experiment are still in existence, and publickly known, by the report of the Royal Society to parliament in 1742, and by the report of a committee of the house of commons in 1758. This gives it a superiority over all the measures which have come to our knowledge.

The first experiment, made with proper atten

tion, that we meet with is by the celebrated Snellius about 1615, and related in his Eratosthenes Batavus. He weighed a Rhinland cubic foot of distilled water, and found it 62-79 Amsterdam pounds. If this was the ordinary weight of the shops, containing 7626 English troy grains, the English cubic foot must be sixty-two pounds nine ounces, only one ounce more than by Everaru's experiment. If it was the mint pound the weight was sixty-two pounds six ounces. The only other trials which can come into competion with Mr. Everard's are some made by the Academy of Sciences at Paris. Picart, in 1691, found the Paris cubic foot of the water of the fountain d'Arcueil to weigh 69.588 lbs. poids de Paris. Du Hamel obtained the very same result; but Mr. Monge, in 1783, says that filtered rain-water of the temperature of 12° (Reaumur) weighs 69-3792. Both these measures are considerably below Mr. Everard's, which is 62.5; the former giving 62-053, and the latte 61.868. M. Lavoisier states the Paris cubic foot at seventy pounds, which makes the English foot 62-47. But there is an inconsistency among them which makes the comparison impossible. Some changes were made in 1688, by royal authority, in the national standards both of weight and length; and the academicians are exceedingly puzzled to this day in reconciling the differences, and cannot even ascertain with perfect assurance the lineal measures which were employed in their most boasted geodetical operations. Such variations in the measurements made by persons of reputation for judgment and accuracy engaged the writer of this article some years ago to attempt another. A vessel was made of a cylindrical form, as being more easily executed with accuracy, whose height and diameter were six inches, taken from a most accurate copy of the exchequer standard. It was weighed in distilled water of the temperature of 55° several times without varying two grains, and it lost 42895 grains. This gives for the cubic foot 998.74 ounces, deficient from Mr. Everard's an ounce and a quarter; a difference which may be expected, since Mr. Everard used the New River water without distillation. These observations cannot be thought superfluous in a matter of such continual reference in the most interesting questions both to the philosopher and the man of business. Let us, therefore, take water for the standard, and suppose that, when of the ordinary temperature of summer and in its state of greatest natural purity, viz. in clean rain or snow, an English cubic foot of it weighs 1000 ounces avoirdupois, of 437.5 troy grains each. Divide the weight of any body by the weight of an equal bulk of water; the quotient is the specific gravity of that body; and, if the three first figures of the decimal be accounted integers, the quotient is the number of avoirdupois ounces in a cubic foot of the body. Thus the specific gravity of the very finest gold which the refiner can produce is 19-365, and a cubic foot of it weighs 19,365 ounces. But an important remark must be made here. All bodies of homogeneous or unorganised texture expand by heat and contract by cooling. The expansion and contraction by the same change of temperature is very different

in different bodies. Thus water, when heated from 60° to 100°, increases its volume nearly of its bulk, and mercury only, and many substances much less. Hence it follows that an experiment determines the specific gravity only in that very temperature in which the bodies are examined. It will therefore be proper always to note this temperature; and it will be convenient to adopt some very useful temperature for such trials in general; perhaps about 60° of Fahrenheit's thermometer is as convenient as any. It may always be procured in these climates with but inconvenience. A temperature near to freezng would have some advantages, because water changes its bulk very little between the temperature 32° and 45°. But this temperature cannot always be obtained. It will much conduce to the facility of the comparison to know the variation which heat produces on pure water. The following table, taken from the observations of Dr. Blagen and Mr. Gilpin (Phil. Trans. 1792), will answer this purpose:

These gentlemen observed the expansion of water to be very anomalous between 32° and 45°. This is distinctly seen during the gradual cooling of water to the point of freezing. It contracts for a while and then suddenly expands. But we seldom have occasion to measure specific gravities in such temperature.

In examining either solids or fluids we must be careful to free their surface, or that of the vessel in which the fluid is to be weighed, from air, which frequently adheres to it in a peculiar manner, and, by forming a bubble, increases the apparent bulk of the solid, or diminishes the capacity of the vessel. The greatest part of what appears on those occasions seems to have existed in the fluid in a state of chemical union, and to be set at liberty by the superior attraction of the fluid for the contiguous solid body. These air bubbles must be carefully brushed off by hand. All greasy matters must be cleared off for the same reason; they prevent the fluid from coming into contact. We must be no less careful that no water is imbibed by the solid, which would increase its weight without increasing its bulk. In some cases, however, a very long maceration and imbibition is necessary. Thus, in examining the specific gravity of the fibrous part of vegeta

bles, we should err exceedingly if we imagined it as small as it appears at first. We believe that in most plants it is at least as great as water, for after long maceration they sink in it.

The nicest and most sensible balances are necessary for this examination. Balances are even constructed on purpose, and fitted with several pieces of apparatus which make the examination easy and neat. We have described (see BALANCE) the most convenient. Mr. Gravesande's contrivance for observing the fractions of a grain is extremely ingenious and expeditious, especially for detecting the effect of viscidity. The hydrometer, or aræometer, is another instrument for ascertaining the specific gravity of fluids. This very pretty instrument is the invention of Hypatia, lady of Alexandria, as eminent for intellectual accomplishments as she was admired for her beauty. She wrote commentaries on Appolonius and Diaphantus, and composed Astronomical Tables; all of which are lost. See HYPATIA. We have described some of the most approved of these instruments under the article HYDROMETER, and shall here make a few observations on the principles of their construction, not as they are usually made accommodated to the examination of particular liquors, but as indicators of pure specific gravity. And we must say that this would, for many reasons, be the best way of constructing them. The very ingenious contrivances for accommodating them to particular purposes are unavoidably attended with many sources of error, both in their adjustment by the maker and in their use; and all that is gained by a very expensive instrument is the saving the trouble of inspecting a table. A simple scale of specific gravity would expose to no error in construction, because all the weights but one, or all the points of the scale but one, are to be obtained by calculation, which is incomparably more exact than any manual operation, and the table can always be more exact than any complex observation. But a still greater advantage is that the instruments would thus be fitted for examining all liquors whatever, whereas at present they are almost useless for any but the one for which they are constructed.

Unless the hydrometer is of a considerable size, it can hardly be made so as to extend from the lightest to the heaviest fluid which we may have occasion to examine, even though we except mercury. Some of the mineral acids are considerably more than twice the weight of ether. When there is such a load at top, the hydrometer is very apt to overset, and inclines with the smallest want of equilibrium. Great size is inconvenient even to the philosopher, because it is not always in his power to operate on a quantity of fluid sufficient to float the instrument. Therefore two, or perhaps three, are necessary for general examination. One may reach from ether to water; another may serve for all liquors of a specific gravity between 1 and 1; and the third, for the mineral acids, may reach from this to 2. If each of these be about two solid inches in capacity, we may easily and expeditiously determine the specific gravity within th part of the truth; and this is precision enough for most purposes of science or business. The chief

questions are, 1. To ascertain the specific gravity of an unknown fluid. This needs no farther explanation. 2. To ascertain the proportion of two fluids which are known to be in a mixture. This is done by discovering the specific gravity of the mixture by means of the hydrometer, and then deducing the proportion from a comparison of this with the specific gravities of the ingredients. In this mode of examination the bulk is always the same; for the hydrometer is immerged in the different fluids to the same depth. Now, if an inch, for example, of this bulk is made up of the heaviest fluid, there is an inch wanting of the lightest; and the change made in the weight of the mixture is the difference between the weight of an inch of the heaviest and of an inch of the lightest ingredients. The number of inches therefore of the heaviest fluid is proportional to the addition made to the weight of the mixture. Therefore let B and b be the bulks of the heaviest and lightest fluids in the bulk 3 of the mixture; and let D, d, and d be the densities, or the weights, or the specific gravities (for they are in one ratio) of the heavy fluid, and the light fluid, and mixture (their bulk being that of the hydrometer). We have ẞ Bb. The addition which would have been made to the bulk ẞ, if the lightest fluid were changed entirely for the heaviest, would be D d; and the change which is really made is d-d. -Therefore ß: b=D—d: 8-d. For similar reasons we should have ß: BD−d: D−8; or, in words, the difference between the specific gravities of the two fluids, is to the difference between the specific gravities of the mixture and of the lightest fluid, as the bulk of the whole to the bulk of the heaviest contained in the mixture;' and the difference of the specific gravities of the two fluids, is to the difference of the specific gravities of the mixture and of the heaviest fluids, as the bulk of the whole to that of the lightest contained in the mixture.' This is the form in which the ordinary business of life requires the answer to be expressed, because we generally reckon the quantity of liquors by bulk, in gallons, pints, quarts. But it would have been equally easy to have obtained the answer in pounds and ounces; or it may be had from their bulks, since we know their specific gravities.

To avoid the inconveniences of a hydrometer with a very long and slender stem, or the necessity of having a series of them, a third sort has been contrived, in which the principle of both are combined. Suppose a hydrometer with a stem, whose bulk is one-tenth of that of the ball, and that it sinks in ether to the top of the stem; it is evident that in a fluid which is one-tenth heavier the whole stem will emerge; for the bulk of the displaced fluid is now one-tenth of the whole less, and the weight is the same as before, and therefore the specific gravity is one-tenth greater. Thus we have obtained a hydrometer which will indicate, by means of divisions marked on the stem, all specific gravities from 0.73 to 0-803; for 0-803 is one-tenth greater than 0.73. These divisions must be made in harmonic progressions, as before directed for an entire scale, placing 0-73 at the top of the stem and 0-803 at the bottom. When it floats at the

lowest division, a weight may be put on the top of the stem, which will again sink it to the top. This weight must evidently be 0-073, or onetenth of the weight of the fluid displaced by the unloaded instrument. The hydrometer, thus loaded, indicates the same specific gravity, by the top of the stem, that the unloaded instrument indicates by the lowest division. Therefore, when loaded, it will indicate another series of specific gravities, from 0-803 to 0.833 (= 0·803 + 0·0803), and will doat in a liquor of the specific gravity 0-8833 with the whole stem above the surface. In like manner, if we take off this weight and put on 1

0.0803, it will sink the hydrometer to the top of the stem; and with this new weight it will indicate another series of specific gravities from 0.8833 to 0.97163 (=0·8833 +008633). And, in the same manner, a third weight = 0-8833 will again sink it to the top of the stem, and fit it for another series of specific gravities up to 1.068793. And thus, with three weights, we have procured a hydrometer fitted for all liquors, from ether to a wort for a malt liquor of two barrels per quarter. Another weight, in the same progression, will extend the instrument to the strongest wort that is brewed. This is a very commodious form of the instrument, and is now in very general use for examining spirituous liquors, worts, ales, brines, and many such articles of commerce. But the divisions of the scale are generally adapted to the questions which naturally occur in the business. Thus, in the commerce of strong liquors, it is usual to estimate the article by the quantity of spirit of a certain strength which the liquor contains.-This we have been accustomed to call proof spirit, and it is such that a wine gallon weighs seven pounds twelve ounces; and it is by this strength that the excise duties are levied. Therefore the divisions on the scale, and the weights which connect the successive repetitions of the scale, are made to express at once the number of gallons, or parts of a gallon, of proof spirits contained in a gallon of the liquor. Such instruments save all trouble of calculation to the exciseman or dealer; but they limit the use of a very delicate and expensive instrument to a very narrow employment. It would be much better to adhere to the expression either of specific gravity or of bulk; and then a very small table, which could be comprised in the smallest case for the instrument, might render it applicable to every kind of fluid. The reader cannot but have observed that the successive weights, by which the short scale of the instrument is extended to a great range of specific gravities, do not increase by equal quantities. Each difference is the weight of the liquor displaced by the graduated stem of the instrument when it is sunk to the top of the scale. It is a determined aliquot part of the whole weight of the instrument so loaded (in our example it is always one-eleventh of it). It increases therefore in the same proportion with the preceding weight of the loaded instrument. In short, both the successive additions, and the whole weights of the loaded instrument, are quantities in geometrical progression; and in like manner the divisions on the scale, if they correspond to equal differences of specific gravity, must also be un