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specific difference in defining things, see DEFINITION.

SPECIES, in logic, is one of the five words called by Porphyry universals. See UNIVERSAL.

SPECIES, in rhetoric, is a particular thing, contained under a more universal

one.

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

SPECIES, in algebra, the characters or symbols made use of to represent quanties.

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

SPECIFIC, in medicine, a remedy, whose virtue and effect is peculiarly adapted to some certain disease, is adequate thereto, and exerts its whole force immediately

thereon.

SPECIFIC gravity, is that by which one body is heavier than another of the same dimension, and is always as the quantity of matter under that dimension. As to the method of finding the specific gravities of bodies, see HYDROSTA

TICS.

SPECTACLE. See VISION.

SPECTRA, ocular. See RETENTION. SPECTRUM, in optics. When a ray of light is admitted through a small hole, and received on a white surface, it forms a luminous spot. If a dense, transparent body be interposed, the light will be refracted, in proportion to the density of the medium; but if a triangular glass prism be interposed, the light is not merely refracted, but it is divided into seven different rays. The ray of light no longer forms a luminous spot, but has assumed an oblong shape, terminating in semicircular arches, and exhibiting seven different colours. This image is called the spectrum, and from being produced by the prism, the prismatic spectrum. These different coloured rays, appearing in different places of the spectrum, show that their refractive power is different. Those which are nearest the middle are the least refracted, and those which are the most distant the greatest. The order of the seven rays of the spectrum is the following: red, orange, yellow, green, blue, indigo, violet. The red, which is at one end of the spectrum, is the least, and the violet, which is at the other end, is the most refracted. Sir Isaac Newton found, if the whole spectrum was divided into 360 parts, the num

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These different coloured rays are not subject to further division. No change is effected upon any of them by being further refracted or reflected; and as they differ in refrangibility, so also do they differ in the power of inflection and reflection. The violet rays are found to be the most reflexible and inflexible, and the red the least.

SPECULATIVE, something related to the theory of some art or science, in contradistinction to practical.

SPECULUM, a looking-glass or mirror, capable of reflecting the rays of the sun, &c. See MIRROR and TELESCOPE.

SPECULUM, in surgery, an instrument for dilating a wound, or the like, in order to examine it attentively.

SPERGULA, in botany, spurrey, a genus of the Decandria Pentagynia class and order. Natural order of Caryophyllei. Essential character: calyx five-leaved; petals five, entire ; capsule ovate, one-celled, five-valved. There are seven species. The S. arvensis, corn spurrey, has linearfurrowed leaves, from eight to twenty in a whorl. The flowers are small, white, and terminal. It is frequent in eorn-fields. In Holland it is cultivated as food for cattle, and has the advantage of growing on the very poorest soils, but does not afford a great deal of food. Poultry are fond of the seeds; and the inhabitants of Finland and Norway make bread of them when their crops of corn fail.

SPERMACETI is found in the head of the Physeter macrocephalus, a species of whale; it is obtained in an unctuous mass, from which oil is obtained by expression. Spermaceti is also found in other cetaceous fishes, and in other parts of the body, mixed with the oil. It is a fine white substance, of a crystallized texture, very brittle, and has little taste or smell. It crystallizes in the form of shining silvery plates. It melts at the temperature of 112°. With a greater heat it may be distilled without change; but, by repeated distillation, it is decomposed, and partly converted into a brown acid liquid. It is soluble in boiling alco

hol, but it separates when the solution cools. It is also soluble in ether, both cold and hot. In the hot solution it concretes on cooling into a solid mass. Spermaceti is scarcely at all soluble in the acids. It combines readily with the pure alkalies, with sulphur, and with the fixed oils. By exposure to the air it becomes rancid. The uses of spermaceti are well known, and particularly in the manufacture of candles. Spermaceti differs chiefly from oil, by its solubility in alcohol and ether. According to Dr. Bostock, it requires 150 times its weight of alcohol, boiling hot, to dissolve it, and as the fluid cools, the spermaceti precipitates.

Spermaceti candles are of modern manufacture: they are made smooth, with a fine gloss, free from rings and scars, superior to the finest wax candles in colour and lustre ; and, when genuine, leave no spot or stain on the finest silk, cloth or linen. A method has been lately proposed by Dr. Smith Gibbes, of Magdalen College, Oxford, to convert animal muscle into a substance much resembling spermaceti. The process is remarkably simple: nothing more is necessary than to take a dead carcase and expose it to a stream of running water: it will in a short time be changed to a mass of fatty matter., To remove the offensive smell, a quantity of nitrous acid may then be poured upon it, which, uniting with the fetid matter, the fat is separated in a pure state. This acid indeed turns it yellow, but it may be rendered white and pure by the action of the oxygenated muriatic acid. Dr. Gibbes brought about the same change in a much shorter time. He took three lean pieces of mutton, and poured on them the three mineral acids, and he perceived, that at the end of three days each was much altered; that in the nitrous acid was much softened, and, on separating the acid from it, he found it to be exactly the same with that which he had before got from the water; that in the muriatic acid was not in that time so much altered; the vitriolic acid had turned the other black. See the article ADIPOCIRE.

SPERMACOCE, in botany, button-weed, a genus of the Tetrandria Monogynia class and order. Natural order of Stellatæ, Rubiaceæ, Jussieu. Essential character: corolla one-petalled, funnel-shaped; seeds two, two-toothed.

species.

There are twenty

SPHÆRANTHUS, in botany, a genus of the Syngenesia Polygamia Segregata class and order. Natural order of Com

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SPHÆRIA, in botany, a genus of the Cryptogamia Fungi. Generic character: fructifications mostly spherical, opening at the top, whilst young filled with jelly, when old with a blackish powder. They grow on the bark or wood of other plants; capsules often immersed, so that their orifices only are visible: most of the species are without a stem.

SPHÆROCARPUS, in botany, a genus of the Cryptogamia Hepaticeæ. Generic character: calyx ventricose, undivided; seeds numerous, collected into a globe.

SPHAGNUM, in botany, a genus of the Cryptogamia Musci. Generic character: male, flower club-shaped; anthers flat; capsule on the same plant, sessile, covered with a lid, without any entire veil; mouth smooth.

SPHERE, is a solid contained under one uniform round surface, such as would be formed by the revolution of a circle about a diameter thereof, as an axis. Thus the circle AE, BD (see Plate XIV. Miscel. fig. 2.) revolving about the diame. ter AB, will generate a sphere, whose surface will be formed by the circumference of the circle.

Definitions. 1. The centre and axis of a sphere are the same as the centre and diameter of the generating circle; and as a circle has an indefinite number of diameters, so a sphere may be considered as having also an indefinite number of diameters, round any one of which the sphere may be conceived to be generated. 2. Circles of the sphere are those circles described on its surface, by the motions of the extremities of the chords ED, FG, IH, &c. at right angles to AB; the diameters of which circles are equal to those chords. 3. The poles of a circle on the sphere are those points on its surface, equally distant from the circumference of that circle: thus A and B are the poles of the circles described on the sphere by the ends of the chords ED, FG, IH, &c. 4. A great circle of the sphere is one equally distant from both its poles; as that described by the extremities of the diameter ED, which is equally distant from both its poles A and B. Lesser circles of the sphere are those which are unequally distant from both their poles; as those described by the extremities of the chords FG, HI, &c. because

unequally distant from their poles A and B. See CIRCLE.

Axioms. 1. The diameter of every great circle passes through the centre of the sphere; but the diameters of all lesser circles do not pass through the same centre: hence also the centre of the sphere is the common centre of all the great circles. 2. Every section of a sphere by a plane, is a circle. 3. A sphere is divided into two equal parts, or hemispheres, by the plane of every great circle: and into two unequal parts, called segments, by the plane of every lesser circle. 4. The pole of every great circle is 90° distant from it on the surface of the sphere; and no two great circles can have a common pole. 5. The poles of a great circle are the two extremities of that diameter of the sphere, which is perpendicular to the plane of that circle. 6. A plane passing through three points on the surface of the sphere, equally distant from any of the poles of a great circle, will be parallel to the plane of that great circle. 7. The shortest distance between two points, on the surface of a sphere, is the arch of a great circle passing through these points. 8. If one great circle meets another, the angles on either side are supplements to each other; and every spherical angle is less than 180°. 9. If two circles intersect each other, the opposite angles are equal. 10. All circles on the sphere, having the same pole, are cut into similar arches, by great circles passing through that pole.

SPHERE, properties of the. 1. All spheres are to one another as the cubes of their diameters. 2. The surface of a sphere is equal to four times the area of one of its great circles, as is demonstrated by Archimedes in his book of the Sphere and Cylinder, lib. i. prop. 37. Hence, to find the superficies of any sphere, we have this easy rule; let the area of a great circle be multiplied by 4, and the product will be the superficies: or, according to Euclid, lib. vi. prop. 20. and lib. xii. prop. 2. the area of a given sphere, CEBD (fig. 3.) is equal to that of a circle, whose radius is equal to the diameter of the sphere BC. Therefore, having measured the circle described with the radius BC, this will give the surface of the sphere. 3. The solidity of a sphere is equal to the surface multiplied into one third of the radius: or, a sphere is equal to two thirds of its circumscribing cylinder, having its base equal to a great circle of the sphere. Let ABEC (fig. 4 and 5.) be the quadrant of a circle, and ABDC the circumscribed square, equal twice VOL. XI.

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the triangle ADC: by the revolution of the figures about the right line AC, as an axis, a hemisphere will be generated by the quadrant, a cylinder of the same base and height of the square, and a cone by the triangle: let these three be cut any how by the plane HF, parallel to the base AB; and the section of the cylinder will be a circle, whose radius is FH; in the hemisphere, a circle whose radius is FE; and in the cone, a circle of the radius FG. But EA (HF1) EFFA2: but AF1 == = FG, because AC CD; and therefore HFEF + FG; or the circle of the radius HF is equal to a circle of the radius EF, together with a circle of the radius GF: and since this is true every where, all the circles together described by the respective radii HF, that is, the cylinder, are equal to all the circles described by the respective radii EF and FG, that is, to the hemisphere and cone taken together. But by Euclid. lib. xii. prop. 10. the cone generated by the triangle DAC, is one third part of the cylinder generated by the square BC; whence it follows, that the hemisphere generated by the rotation of the quadrant ABEC, is equal to the remaining two-thirds of the cylinder, and that the whole sphere is two-thirds of the cylinder circumscribed about it. Hence it follows, that a sphere is equal to a cone whose height is equal to the semi-diameter of the sphere, and its base equal to the superfices of the sphere, or to the area of four great circles of the sphere, or to that of a circle, whose radius is equal to the diameter of the sphere.

SPHERE, in astronomy, that concave orb, or expanse, which invests our globe, and in which the heavenly bodies appear to be fixed, and at an equal distance from the eye. The better to determine the places of the heavenly bodies in the sphere, several circles are supposed to be described on the surface thereof, hence called the circles of the sphere: of these, some are called great circles, as the equinoctial, ecliptic, meridian, &c. and others, small circles, as the tropics, parallels, &c. See each under its proper article.

SPHERICS, is that part of geometry which treats of the position and mensura. tion of arches of circles described on the surface of a sphere. See SPHERE,

SPHEROID, in geometry, a solid, approaching to the figure of a sphere.

The spheroid is generated by the entire revolution of a semi-ellipsis about its axis. Thus, if the semi-ellipsis AHFB p d

(Plate XIV. Miscel. fig. 6.) be supposed to revolve round its transverse axis AB, it will generate the oblong spheroid AHFBC. Now as all circles are as the squares described upon their radii, that is, the circle of the radius EH is to the circle of the radius EG, as CF to CD, because EH: EG:: CF: CD, and since it is so every where, all the circles described with the respective radii EH, (that is, the spheroid made by the rotation of the semi-ellipsis AFB about the axis AB) will be to all the circles described by the respective radii EG, (that is, the sphere described by the rotation of the semicircle ABD on the axis AB,) as FC to CD; that is, as the spheroid is to the sphere on the same axis, so is the other axis of the generating ellipsis to the square of the diameter or axis of the sphere and this holds, whether the spheroid be formed by a revolution around the greater or lesser axis.

Hence it appears, that the half of the spheroid, formed by the rotation of the space AHFC, around the axis AC, is double of the cone generated by the triangle AFC, about the same axis. Hence, also, is evident the measure of segments of the spheroid, cut by planes perpendicular to the axis: for the seg ment of the spheroid, made by the rotation of the space ANHE round the axis AE, is to the segment of the sphere, having the same axis AC, and made by the rotation of the segment of the circle AMGE, as CF to CD. But the measure of this solid may be found with less trouble by this analogy; viz. as BE: ACEB: so is the cone generated by the rotation of the triangle AHE round the axis AE; to the segment of the sphere made by the rotation of the space ANHE round the same axis AE, as is demonstrated by Archimedes of conoids and spheroids, prop. 34. This agrees as well to the oblate as to the oblong spheroid. A spheroid is also equal to two thirds of its circumscribing cylinder. As to the superficies of a spheroid, M. Huygens gives the two following constructions in his Horolog. Oscill. For describing a circle equal to the superficies of an oblong and prolate spheroid: 1. Let an oblong spheroid be generated by the rotation of the ellipsis ADBE, (fig. 7.) about its transverse axis AB, and let DE be its conjugate; make DF equal to CB, or let F be one of the foci, and draw BG parallel to FD, and about the point G, with the radius BG, describe an arch, BHA, of a circle; then between the semi-conjugate CD,

and a right line equal to DE+ the arch AHB, find a mean proportional, and that will be the radius of a circle equal to the superficies of the oblong spheroid. 2. Let a prolate spheroid be generated by the rotation of the ellipsis ADBE (fig. 8.) about its conjugate axis AB. Let F be one of the foci, and bisect CF in G, and let AGB be the curve of the common parabola, whose base is the conjugate diameter AB, and axis CG. Then if between the transverse axis DE, and a right line equal to the curve AGB of the parabola, a mean proportional be taken, the same will be the radius of a circle equal to the surface of that prolate spheroid.

SPHEX, in natural history, a genus of insects of the order Hymenoptera. Mouth with an entire jaw, the mandibles horny, incurved, toothed; lip horny, membranaceous at the tip; four feelers; antennæ with about ten articulations; wings, in each sex, plane, incumbent, and not folded; sting pungent, and concealed within the abdomen. There are about one hundred and fifty species, divided into sections. A. antennæ setaceous: an entire lip and no tongue. B. antennæ filiform; lip emarginate, with a bristle on each side; tongue inflected, trifid. The insects of this genus are the most savage and rapacious of this class of beings: they attack whatever comes in their way, and by means of their poisonous sting overcome and devour others far beyond their own size. Those belonging to section B are found chiefly on umbellate plants: the larva is without feet, soft, and inhabits the body of some other insect, on whose juices it exists: the pupa has rudiments of wings.

S. maculata, is found in England. Thorax spotted; first segment of the abdomen with a white dot on each side; second, edged with white. See Plate IV. Entomology, fig. 6.

S. figulus, an inhabitant of Upsal, is smooth and black; segments of the abdomen at the edges and lip lucid. It is found in holes of wooden partitions, abandoned by other insects; these it cleanses by gnawing round them, and, placing a piece of moist clay at the bottom, sticks a spider upon it; in the body of this spider it deposits its eggs, and then closes up the entrance with clay, and leaves it to be devoured by the larva.

S. spirifex, is black; thorax hairy, immaculate; petiole of one joint yellow, as long as the abdomen. This insect is found in Egypt, and in several parts of

Europe, in cylindrical cavities, wrought within like a honey-comb, on the sides of cliffs, and in the mud walls of cottages.

S. figulus, is one of the species mentioned by Dr. Shaw This insect, having found some convenient cavity, seizes a spider, and having killed it, deposits it at the bottom; then laying her egg in it, she closes up the orifice of the eavity with clay; the larva, which resembles the maggot of a bee, having devoured the spider, spins itself up in a dusky silken web, and changes into a chrysalis, out of which, within a certain number of days, proceeds the complete insect. The female of this species prepares several separate holes, or nests, in each of which she places a dead insect and an egg; each cell costing her the labour of about two days.

SPHINCTER, in anatomy, a term applied to a kind of circular muscles, or muscles in form of rings, which serve to close and draw up several orifices of the body, and prevent the excretion of the contents: thus the sphincter of the anus closes the extremity of the intestinum rec

tum.

SPHINX, in natural history, hawk-moth, a genus of insects of the order Lepidop. tera. Antennæ somewhat prismatic, tapering at each end; tongue mostly exserted; two feelers, reflected; wings deflected. There are about two hundred species; these fly abroad in the morning and evening, are very slow on the wing, and often make a humming kind of noise; they extract the nectary of flowers with the tongue: the larva has sixteen feet; and is pretty active. The name of the sphinx is applied to the genus, on account of the posture assumed by the larva of several of the larger species, which are said to be seen in an attitude much resembling that of the Egyptian sphinx. This numerous genus is divided into sections: A. antennæ scaly feelers hairy; tongue spiral. B. antennæ cylindrical; tongue exserted, truncate; wings entire. C. antennæ thicker in the middle; tongue exserted. The largest, and perhaps the most beautiful of the European species, is S. atropos; of this, the upper wings are of a fine dark grey, with a few slight variegations of dull orange and white; the body is orange coloured, with the sides marked with black bars, while along the top of the back, from the thorax to the tail, runs a broad blue-grey stripe; on the top of the thorax is a very large patch, of a most singular appearance,

exactly resembling the usual figure of a skull When in the least disturbed, or irritated, this insect emits a sound like the squeaking of a mouse or a bat. In many parts of Europe it is held much in dread by the vulgar, and regarded as the harbinger of misfortune. The caterpillar, from which this curious sphinx proceeds, is in the highest degree beautiful, and surpasses in size every other European insect of the kind, being sometimes five inches in length: its colour is a bright yellow, the sides marked by a row of se ven most elegant broad stripes, of a mixed violet and sky-blue colour; on the last joint of the body is a horn, or process, hanging over the joint in the manner of a tail, having a rough or muricated surface, and a yellow colour. This caterpillar is principally found on the potatoe and the jasmine; it usually changes into a chrysalis in the month of September, retiring for that purpose pretty deep under the surface of the earth; the complete insect emerging in the following summer. This species is generally considered as a very rare insect; and as the caterpillar feeds chiefly by night, concealing itself during the day, it is not often seen. See Plate IV. Entomology, fig. 7.

S. ligustri, or privet hawk-moth, is a large insect, measuring nearly four inches and a half from wing's end to wing's end: the upper wings of a brown colour, most elegantly varied or shaded with deeper and lighter streaks and patches; the under wings and body are of a fine rose colour, barred with transverse black stripes. The caterpillar, which is very large, is smooth, and of a fine green, with seven oblique purple and white stripes along each side; at the extremity of the body, or top of the last joint, is a horn or process pointing backwards. This beautiful caterpillar is often found in the months of July and August feeding on the privet, the lilac, the poplar, and some other trees, and generally changes to a chrysalis in August or September, retiring for that purpose to a considerable depth beneath the surface of the ground, and, after casting its skin, continuing during the whole winter in a dormant state, the sphinx emerging from it in the succeeding June.

S. ocellata is perhaps still more beautiful: it is rather a smaller insect than the preceding, and has the upper wings and body brown; the former finely clouded with different shades, while the lower wings are of a bright rose-colour, each marked with a large ocellated black spot.

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