See PERCA, ICHTHYOLOGY Index.

PEARL-Glue, the name of a kind of glue, of remarkable strength and purity, made from the skins of pearsches.

in Natural History, a hard, white, shining body, usually roundish, found in a teffaceous fish, a species of Mya; which see, CONCHOLOGY Index.

Pearls, though esteemed of the number of gems, and highly valued in all ages, proceed only from a distemper in the animal that produces them, analogous to the bezoars and other stony concretions in several animals of other kinds. For an account of the mode of formation of the pearl, see CONCHOBGY, p. 476; for the history of the pearl fishery in the bay of Condatchy in Ceylon, see CEYLON, p. 363; see also Cordier's History of that island, 4to.

Mr Bruce mentions a mulete found in the salt springs of the Nubian desert; in many of which he found those excrescences which might be called pearls, but all of them ill formed, foul, and of a bad colour, though of the same consistence; and lodged in the same part of the body as those in the sea. "The mulete, too (says our author), is in every respect similar, I think larger. The outer skin or covering of it is of a vivid green. Upon removing this, which is the epidermis, what next appears is a beautiful pink without glofs, and seemingly of a calcareous nature. Below this, the mother-of-pearl, which is undermost, is a white without lustr, partaking much of the blue and very little of the red; and this is all the difference I observed between it and the pearl-bearing mulete of the Red sea."

"In Scotland, especially to the northward, in all rivers running from lakes, there are found muletes that have pearls of more than ordinary merit, though seldom of large size. They were formerly tolerably cheap, but lately the wearing of real pearls coming into fashion, those of Scotland have increased in price greatly beyond their value, and superior often to the price of oriental ones when bought in the east. The reason of this is a demand from London, where they are actually employed in work, and sold as oriental. But the excellency of all glafs or past manufactory, it is likely, will keep the price of this article, and the demand for it, within bounds, when every lady has it in her power to wear in her ears, for the price of sixpence, a pearl as beautiful in colour, more elegant in form, lighter and easier to carry, and as much bigger as the pleases, than the famous ones of Cleopatra and Servilia." In Scotland, as well as in the east, the smooth and perfect shell rarely produces a pearl; the crooked and distorted shell seldom wants one.

The mother-of-pearl manufactory is brought to the greatest perfection at Jerusalem. The most beautiful shell of this kind is that of the penimim already mentioned; but it is too brittle to be employed in any large pieces of workmanship; whence that kind named dora is most usually employed; and great quantities of this are daily brought from the Red sea to Jerusalem. Of these, all the fine works, the crucifixes, the wafer-boxes, and the beads, are made, which are sent to the Spanish dominions in the New World, and produce a return incomparably greater than the staple of the greatest manufactory in the Old.

Very little is known of the natural history of the pearl fish. Mr Bruce says, that, as far as he has observed, they are all stuck upright in the mud by an extremity; the mulete by one end, the pinna by the small sharp point, and the third by the hinge or square part which projects from the round. "In shallow and clear streams (says Mr Bruce), I have seen small furrows or tracks upon the sandy bottom, by which you could trace the mulete from its last station; and these not straight, but deviating into traverses and triangles, like the course of a ship in a contrary wind laid down upon a map, probably in pursuit of food. The general belief is, that the mulete is constantly stationary in a state of repose, and cannot transfer itself from place to place. This is a vulgar prejudice, and one of those facts that are mistaken for want of sufficient pains or opportunity to make more critical observations. Others, finding the first opinion a false one, and that they are endowed with power of changing place like other animals, have, upon the same foundation, gone into the contrary extreme, so far as to attribute swiftness to them, a property purely inconsistent with their being fixed to rocks. Pliny and Solinus say that the muletes have leaders, and go in flocks; and that their leader is endowed with great cunning to protect himself and his flock from the fishers; and that, when he is taken, the others fall an easy prey. This, however, we may justly look upon to be a fable; some of the most accurate observers having discovered the motion of the mulete, which indeed is wonderful, and that they lie in beds, which is not at all so, have added the rest, to make their history complete." Our author informs us, that the muletes found in the salt springs of Nubia likewise travel far from home, and are sometimes surprised, by the ceasing of the rains, at a greater distance from their beds than they have strength and moisture to carry them. He affirms us, that none of the pearl-fish are eatable; and that they are the only fish he saw in the Red sea that cannot be eaten.

Artificial Pearls. Attempts have been made to take out stains from pearls, and to render the foul opaque-coloured ones equal in lustre to the oriental. Numerous processes are given for this purpose in books of secrets and travels; but they are very far from answering what is expected from them. Pearls may be cleaned indeed from any external foulness by washing and rubbing them with a little Venice soap and warm water, or with ground rice and salt, with starch and powder blue, plaster of paris, coral, white vitriol and tartar, cuttle-bone, pumice-stone, and other similar substances; but a stain that reaches deep into the substance of pearls is impossible to be taken out. Nor can a number of small pearls be united into a mass similar to an entire natural one, as some pretend.

There are, however, methods of making artificial pearls, in such manner as to be with difficulty distinguished from the best oriental. The ingredient used for this purpose was long kept a secret; but it is now discovered to be a fine silver-like substance found upon the under side of the scales of the baly or bleak fish. The scales, taken off in the usual manner, are washed and rubbed. rubbed with fresh parcels of fair water, and the several liquors suffered to settle; the water being then poured off, the pearly matter remains at the bottom, of the confluence of oil, called by the French essence d'oriente. A little of this is dropped into a hollow bead of blue glass, and thaken about so as to line the internal surface; after which the cavity is filled up with wax, to give solidity and weight. Pearls made in this manner are distinguishable from the natural only by their having fewer blemishes.

Mother-of-PEARL, the shell, not of the pearl oyster, but of the mytilus margaritiferus. See MYTILUS, CONCHOLOGY Index.