cle, distributed about the surface, and retractile within it. This is found in vast numbers in the brain, or spinal marrow, immediately beneath the brain of sheep. These noxious animalcules occasion giddiness and staggering, and the disease known by the name of the dunt or rickets, which, if the containing vesicle be broken, is incurable; for these minute worms, in size scarcely larger than a grain of sand, are each of them furnished with from thirtytwo to thirty-six hooks on the head, by which they fix themselves firmly to the substance of the brain, or its coats.

The structure and physiology of the tænia are curious, and it may be amusing as well as instructive to consider it with attention. The tænia appears destined to feed upon such juices of animals as are already animalized; and is therefore most commonly found in the alimentary canal, and in the upper part, where there is the greatest abundance of chyle; for chyle seems to be the natural food of the tænia. As it is thus supported by food which is already digested, it is destitute of the complicated organs of digestion. As the T. solium is most frequent in this country, it may be proper to describe it more particularly.

It is from three to thirty feet long, some say sixty feet. It is composed of a head, in which are a mouth adapted to drink up fluids, and an apparatus for giving the head a fixed situation. The body is composed of a great number of distinct pieces articulated together, each joint having an organ by which it attaches itself to the neighbouring part of the inner coat of the intestine. The joints nearest the head are always small, and they become gradually enlarged as they are farther removed from it; but towards the tail a few of the last joints again become diminished in size. The extremity of the body is terminated by a small semicircular joint, which has no opening in it.

The head of this animal is composed of the same kind of materials as the other

parts of its body; it has a rounded opening at its extremity, which is considered to be its mouth. This opening is continued by a short duct into two canals; these canals pass round every joint of the animal's body, and convey the aliment. Surrounding the opening of the mouth, are placed a number of projecting radii, which are of a fibrous texture, whose direction is longitudinal. These radii appear to serve the purpose of tentacula for fixing the orifice of the mouth, as well as that of muscles to expand the cavity of the

mouth, from their being inserted along the brim of that opening. After the rounded extremity or head has been narrowed into the neck, the lower part becomes flatted, and has two small tubercles placed upon each flatted side; the tubercles are concave in the middle, and appear destined to serve the purpose of suckers for attaching the head more effectually. The internal structure of the joints composing the body of this animal is partly vascular and partly ceilular; the substance itself is white, and somewhat resembles in its texture the coagulated lymph of the human blood. The alimentary canal passes along each side of the animal, sending a cross canal over the bottom of each joint, which connects the two lateral canals together.

Mr. Carlisle injected with a coloured size, by a single push with a small syringe, three feet in length of these canals, in the direction from the mouth downwards. He tried the injection the contrary way, but it seemed to be stopped by valves. The alimentary canal is impervious at the extreme joint, where it terminates without any opening analogous to an anus. Each joint has a vascular portion occupying the middle part, which is composed of a longitudinal canal, from which a great number of lateral canals branch off at right angles. These canals contain a fluid like milk.

The tænia seems to be one of the simplest vascular animals in nature. The way in which it is nourished is singular; the food being taken in by the mouth, passes into the alimentary canal, and is thus made to visit, in a general way, the different parts of the animal. As it has no excretory ducts, it would appear that the whole of its alimentary fluid is fit for nourishment; the decayed parts probably dissolve into a fluid which transudes through the skin, which is extremely porous.

This animal has nothing resembling a brain or nerves, and seems to have no organs of sense but those of touch. It is most probably propagated by ova, which may easily pass along the circulating vessels of other animals. We cannot otherwise explain the phenomena of worms being found in the eggs of fowls, and in the intestines of a foetus before birth, except by supposing their ova to have passed through the circulating vessels of the mother, and by this means been conveyed to the fœtus.

The chance of an ovum being placed inasituation where it will be hatched, and the young find convenient subsistence, must be very small; hence the necessity

for their being very prolific. If they had the same powers of being prolific which they now have, and their ova were afterwards very readily hatched, then the multiplication of these animals would be immense, and become a nuisance to the other parts of the creation.

Another mode of increase allowed to tania (if we may call it increase) is by an addition to the number of their joints. If we consider the individual joints as distinct beings, it is so; and when we reflect upon the power of generation given to each joint, it makes this conjecture the more probable. We can hardly suppose that an ovum of a tænia, which at its full growth is thirty feet long, and composed of four hundred joints, contained a young ta nia, composed of this number of pieces; but we have seen young tænia not half a foot long, and not possessed of fifty joints, which still were entire worms. We have also many reasons to believe, that when a part of this animal is broken off from the rest, it is capable of forming a head for itself, and becomes an independent being. The simple construction of the head makes its regeneration a much more easy operation than that of the tails and feet of lizards, which are composed of bones and complicated vessels; but this last operation has been proved by the experiments of Spallanzani and many other naturalists.

TAFFETY, in commerce, a fine smooth silken stuff, remarkably glossy. See SILK. There are taffeties of all colours, some plain, and others striped with gold, silver, &c. others chequered, others flowered, &c. according to the fancy of the workmen.

TAGETES, in botany, marygold, a genus of the Syngenesia Polygamia Superflua class and order. Natural order of Composite Oppositifolia. Corymbiferæ, Jussieu. Essential character: calyx oneleaved, five-toothed, tubular; florets of the ray five, permanent; down with firm erect chaffs, receptacle naked. There are four species, and several varieties; the T. erecta, African marygold, is from three to four feet in height, divided from the middle into many branches, each bearing one large flower; leaves long, pinnate; leaflets dark green; flowers yellow, from brimstone to orange colour; of this there are five varieties, all annuals.

TALC, in mineralogy is divided into three sub-species, viz. 1. The earthy talc, which is a greenish white colour, composed of glimmering pearly small scaly parts it soils a little, and feels rather greasy. It occurs in the tin mines near

This is frequently confounded with mica, from which it is, however, distinguished by want of elasticity, by its greasy feel, and colour. It is almost entirely confined to the primitive mountains, where it occurs in beds, imbedded in serpentine, and also in veins. It abounds in the mountains of Tyrol and Salzburg, hence it is brought to Venice, and on that account has obtained the name of Venetian talc. It is employed as a basis for coloured crayons, and for the finest rouge.

3. Indurated talc is of a greenish grey colour: it occurs massive; lustre shining, passing to glistening, and is pearly, feels rather greasy. It occurs in primitive mountains, where it forms beds in clay, slate, and serpentine. It is thought to be an intermediate link between steatite and pot-stone, which see. It is found in the Alps, in Stiria, and in Austria, and Hungary: also in some parts of Scotland: the constituent parts are,

pearing, or on their appearance, challenged and disallowed, when the judge, upon motion, orders a supply to be made by the sheriff of one or more such persons as are present in court, to make up a full jury.

TALLOW tree, a remarkable tree, growing in great plenty in China; so called from its producing a substance like tallow, which serves for the same purpose; it is about the height of a cherry-tree, its leaves in form of a heart, of a deep shining red colour, and its bark very smooth. Its fruit is inclosed in a kind of pod, or cover, like a chesnut, and consists of three round white grains, of the size and form of a small nut, each having its peculiar capsule, and within a little stone. This stone is encompassed with a white pulp, which has all the properties of true tallow, both as to consistence, colour, and even smell; and accordingly the Chinese make their candles of it; which would doubtless be as good as those in Europe, if they knew how to purify their vegetable, as well as we do our animal tallow. All the preparation they give it is, to melt it down, and to mix a little oil with it, to make it softer and more pliant. It is true, their candles made of it yield a thicker smoke, and a dimmer light than ours; but these defects are owing in a great measure to the wicks, which are not of cotton, but only a little rod of dry light wood, covered with the pith of a rush wound round it; which, being very porous, serves to filtrate the minute parts of the tallow, attracted by the burning stick, which, by this means, is kept alive. See TOMEX.

TALPA, the mole, in natural history, a genus of Mammalia, of the order Feræ. Generic character: six fore-teeth in the upper jaw, unequal, eight in the lower; tusks solitary, in the upper jaw larger; seven grinders in the upper, and six in the lower. There are four species.

T. Europea, the European mole, is about six inches in length, without the tail. Its body is large and cylindrical, and its snout strong and cartilaginous. Its skin is of extraordinary thickness, and covered with a fur, short, but yielding to that of no other animal in fineness. It hears with particular acuteness, and, notwithstanding the popular opinion to the contrary, possesses eyes, which it is stated to be able to withdraw, or project, at pleasure. It lives partly on the roots of vegetables, but principally on animal food, such as worms and insects, and is extremely voracious and fierce. Shaw

relates, from Sir Thomas Brown, that a mole, a toad, and a serpent, have been repeatedly inclosed in a large glass vase, and that the mole has not only killed the others, but has devoured a very considerable part of them. It abounds in soft ground, in which it can dig with ease, and which furnishes it with the greatest supply of food. It forms its subterraneous apartments with great facility by its snout and feet, and with a very judicious reference to escape and comfort. It produces four or five young in the spring, in a nest a little beneath the surface, composed of moss and herbage. It is an animal injurious to the grounds of the farmer, by throwing up innumerable hills of mould, in the construction of its habitation, or the pursuit of its food, and many persons in England obtain their subsistence from the premiums which are, on this account, given for their destruction. Moles can swim with considerable dexterity, and are thus furnished with the means of escape, in those sudden inundations to which they are frequently exposed. In Ireland, the mole is unknown. See Mammalia, Plate XX. fig. 5.

T. radiata, or the radiated mole, is very similar to the above, from which it is principally distinguished by a circle of radiated tendrils resembling the ray of a boot-spur, attached to the nose. It is a native of North America. See Mammalia, Plate XX. fig. 6.

The common mole of North America belongs to the genus Sorex: its specific name is Aquaticus.

TALUS, in fortificaton.

Talus of a

bastion, or rampart, is the slope or diminution allowed to such a work, whether it be of earth or stone, the better to support its weight. The exterior talus of a work is its slope on the side towards the country, which is always made as little as possible, to prevent the enemy's scalade; unless the earth be bad, and then it is absolutely necessary to allow a considerable talus for its parapet. The interior talus of a work is its slope on the inside towards the place.

TAMARINDUS, in botany, tamarind tree, a genus of the Monadelphia Triandria class and order. Natural order of Lomentacea. Leguminosa, Jussieu. Essential character: calyx four-parted; petals three; nectary of two shorter bristles under the filaments; legume pulpy. There is only one species, viz. T. indica, tamarind tree, which grows to a large size in those countries where it is a native; the stem is very large, covered

with a brown bark, dividing into many branches at the top, and spreading wide every way; the flowers come out from the side of the branches, five, six, or more together, in loose branches; the pods are thick and compressed; those from the West Indies are from two to five inches in length, containing two, three, or four seeds; those from the East Indies are nearly twice as long, and contain five, six, and even seven seeds; plants raised from both these are so much alike as not to be distinguished; the difference in the size of the pods is probably owing to soil and culture. The calyx is straw-coloured; the petals are yellowish, beautifully variegated with red veins; peduncles half an inch in length, each furnished with a joint, at which the flower turns inward; filaments commonly three; they are purple, and the anthers are brownish. The timber of the tamarind-tree is heavy, firm, and hard; sawn into boards, it is converted to many useful purposes in building. The fruit is used both in food and medicine. In many parts of America, particularly in Curracoa, they eat abundance of it raw, without any inconvenience. In Martinico, also, they eat the unripe fruit, even of the most austere kind.

TAMARIX, in botany, tamarisk, a genus of the Pentandria Trigynia class and order. Natural order of Succulentæ. Portulaceæ, Jussieu. Essential character: calyx five-parted; petals five; capsule one-celled, three-valved; seeds pappose. There are four species: we shall notice the T. gallica, French tamarisk, which is a native of the south of France, Spain, Italy, Russia, Tartary, Barbary, and Japan, where it grows to a tree of a middling size; in England it is rarely more than fourteen feet in height. The bark is rough, and of a dark brown colour; it sends out many slender branches, most of which spread out flat, hanging downwards at their ends; these are covered with a chesnut coloured bark, and garnished with very narrow, finely-divided leaves, of a bright green colour, having small leaves or indentures, which lie over each other like scales of fish; the flowers are produced in taper spikes, at the end of the branches, several of them growing on the same branches; the spikes are about an inch long; the flowers are set very close all round the spike; they are small, and have five concave petals, of a pale flesh colour, with five slender stamina, terminated by roundish red anthers; the flowers appear in July, and

are succeeded by oblong, acute-pointed. three-cornered capsules, filled with small downy seeds, which seldom ripen in England.

TAMBAC, a mixture of gold and copper, which the people of Siam hold more beautiful, and set a greater value on, than gold itself.

TAMBOUR, in architecture, a term applied to the Corinthian and Composite capitals, as bearing some resemblance to a drum, which the French call tambour.

TAMBOUR is also used for a little box of timber-work, covered with a ceiling, within side the porch of certain churches, both to prevent the view of persons passing by, and to keep off the wind, &c. by means of folding doors.

TAMUS, in botany, black bryony, a genus of the Dioecia Hexandria class and order. Natural order of Sarmentaceæ. Asparagi, Jussieu. Essential character: calyx six-parted; corolla none; female, style trifid; berry three-celled, inferior; seeds two. There are two species, viz. T. communis, common black bryony, and T. cretica, Creton black bryony.

TANACETUM, in botany, tansey, agenus of the Syngenesia Polygamia Superflua class and order. Natural order of Composite Discoideæ. Corymbiferæ, Jussieu. Essential character: calyx imbricate, hemispherical; corolla rays obsolete, trifid, sometimes none, and all the flowers hermaphrodite; down submarginate; receptacle naked. There are nine species, of which the T. vulgare, common tansey, has a fibrous creeping root, which spreads to a great distance; the herb is bitter, possessing a strong aromatic smell. It is a native of Europe and Siberia, in high meadows and pastures, on the banks of rivers, and in swampy places, flowering from June to August.

TANAECIUM, in botany, a genus of the Didynamia Angiospermia class and order. Essential character: calyx cylindrical, truncate; corolla tubular, almost equal, five-cleft; rudiment of a fifth filament; berry corticose, very large. There are two species, viz. T. jaroba, and T. parasiticum, both natives of Jamaica.'

TANAGRA, the tanager, in natural history, a genus of birds of the order Passeres. Generic character: bill conic somewhat inclining towards the point; upper mandible slightly ridged and notched near the end. There are forty-four species, of which the following deserve the chief attention.

T. jacapa, or the red-breasted tanager,

is of the size of a sparrow, and abounds in various parts of America. It feeds on fruits, and frequents gardens. Its nest is of a cylindrical form, fixed to the horizontal branch of a tree, and the entrance is beneath. It is generally seen in pairs.

The T. tatoa, or titmouse of Paradise, is nearly as large as a goldfinch, is one of the most beautiful birds of the genus, adorned with the most brilliant plumage of scarlet, blue, green, and gold. It is found in flocks in Cayenne and Guiana, at the season when a particular, but undescribed fruit tree is in bearing, and is said to be found, in those countries, only in the immediate vicinity of these trees. It may be confined, and fed on bread and milk; but has no powers of melody.

TANGENT, in geometry, is defined, in general, to be a right line, which touches any arch of a curve, in such a manner, that no right line can be drawn between the right line and the arch, or within the angle that is formed by them The tangent of an arch is a right line drawn perpendicularly from the end of a diameter, passing to one extremity of the arch, and terminated by a right line drawn from the centre through the other end of the arch, and called the secant. And the co-tangent of an arch is the tangent of the complement of that arch. The tangent of a curve is a right line, which only touches the curve in one point, but does not cut it.

In order to illustrate the method of drawing tangents to curves, let A C G, Plate XIV. Miscel. fig. 10. be a curve of any kind, and C the given point from whence the tangent is to be drawn. Then conceive a right line mg, to be carried along uniformly, parallel to itself, from A towards Q and let, at the same time, a point, p, so move in that line, as to describe the given curve, A C G; also let mm, or C n, express the fluxion of Am, or the velocity wherewith the line mg, is carried; and let n S express the corresponding fluxion of m p, in the position m C g, or the velocity of the point, p, in the line mg moreover, through the point, C, let the right line, S F, be drawn, meeting the axis of the curve, A Q, in F.

Now it is evident, that if the motion of , along the line mg, was to become equable at C, the point, p, would be at S, when the line itself had got into the position m Sg; because, by the hypothesis, Cn and n S express the distances that might be described by the two uniform motions in the same time. And if ws g be assumed to represent any other position of that line, and s the contemporary

:

position of the point, p, still supposing an equable velocity of p; then the distances, Cv, and v s, gone over in the same time by the two motions, will always be to each other as the velocities, or as Cn to n S. Therefore, since Cv vs :: Cn: n S, (which is a known property of similar triangles,) the point, s, will always fall in the right line, FC S, (fig. 11.): whence it appears, that if the motion of the point, p, along the line, mg, was to become uniform at C, that point would then move in the right line, Ċ S, instead of the curve line, C G. Now, seeing the motion of p, in the description of curves, must either be an accelerated or retarded one; let it be first considered as an accelerated one, in which case the arch, C G, will fall wholly above the right line, CD, as in fig. 10.; because the distance of the point, p, from the axis A Q, at the end of any given time, is greater than it would be if the acceleration was to cease at C; and if the acceleration had ceased at C, the point, p, would have been always found in the said right line, F S. But if the motion of the point, p, be a retarded one, it will appear, by arguing in the same man

ner,

that the arch C G, will fall wholly below the right line, C D, as in fig. 11.

This being the case, let the line mg, and the point p, along that line, be now supposed to move back again, towards A and m, in the same manner they proceeded from thence; then, since the velocity of p did before increase, it must now, on the contrary, decrease; and therefore, as p, at the end of a given time, after repassing the point, C, is not so near to A Q, as it would have been, had the velocity continued the same as at C, the arch, Ch (as well as C G) must fall wholly above the right line, FCD: and by the same method of arguing, the arch, Ch, in the second case, will fall wholly below F C D. Therefore F C D, in both cases, is a tangent to the curve at the point, C ; whence the triangles, Fm C, and Cn S, being similar, it appears that the subtangent, m F, is always a fourth proportional to n S, the fluxion of the ordinate, C n, the fluxion of the absciss, and C m, the ordinate: that is, Sn: n G :: mCm F. Hence, if the absciss, A m and the ordinate mpy, we shall have mF=;

X,

yx y

by means of which general expression, and the equation expressing the relation between and y, the ratio of the fluxions,

and y will be found, and from thence the length of the sub-tangent, m F, as in the following examples.