age from 86 and divide the remainder by 2." Life annuities and the expectation of life are not calculated in this way now, but from tables of real observations, nevertheless, the rule just mentioned agrees nearly or within a few months with the deductions taken from such tables, and may always serve in rough calculations.

COMPLEMENT, in astronomy, the distance of a star from the zenith, or the arch comprehended between the place of the star above the horizon and the zenith.

COMPLEMENT, in geometry, is what remains of a quadrant of a circle, or of 90° after any arch is taken away.

COMPLEMENTS of a parallelogram, are the two smaller parallelograms made by drawing two right lines through the point of a diagonal and parallel to the sides of the parallelogram.

COMPLEXION, among physicians, the temperament, habitude, and natural disposition of the body; but, in general use, the word means the colour of the skin. Dr. Hunter has given the following view of the different complexions observable among mankind:

Black.

Swarthy

Africans under the line,
Inhabitants of New Guinea,
Inhabitants of New Holland.

Moors in the north of Africa.
Hottentots in the South of
Africa.

Copper-coloured. East Indians.
Red-coloured. Americans.

Brown coloured. Tartars.

Persians,

COMPOSITION of motion, is an assemblage of several directions of motion, resulting from several powers acting in different, though not opposite directions. See MECHANICS.

COMPOST, in agriculture, an artificial manure, contrived with a view to this advantage: that, cheaper and less bulky than the quantity of dung required for an equal extent of soil, it shall yet produce equal effects.

COMPOUND Interest, see INTEREST.

CONCENTRATION, the act of increasing the strength of fluids, either by evaporating the water with which spirits or acids are combined, or by exposing them to severe frost, when the water will be frozen and the acid or spirits will be found in the middle of the ice.

CONCHOLOGY, the study or science of shells or testaceous animals, is a branch of natural history. Shells may be said to constitute a department of rational enquiry worthy the researches of the man of science; and when we consider the amazing diversity of singular and beautiful objects that they embrace, they are such as cannot fail to arrest, in a particular degree, the regard of every observer. The term conchology, comprehends the study of animals which have a testaceous covering, whether inhabitants of the land or the water. Testaceology is a term synonymous with conchology, but is of later origin and application. All testaceous animals are composed of two parts, one of which, the animal itself, is soft and moluscous: the other is the shell or habitation, which is hard, of a stony or calcareous nature, and either partially or entirely covers the animal. The animal is attached to the shell by means of ligaments or muscles. It was long considered as a matter of dispute among naturalists whether the arrangement of shells should be constituted from the animals or their habitation. There is much difficulty in either plan of proceeding; but the latter is now generally adopted, because it is certain that the best characters upon which to found all systems of natural history, must be those most obvious and accessible. All ranks of animals, as nearly as can be with convenience, should be arranged by apparent and external cha

racters.

All shells or testaceous bodies hitherto discovered, may be divided into three principal tribes, which may be denominated univalve, bivalve, and multivalve. Any external part of a shell being of a

testaceous substance, and either itself forming a shield or covering for the animal, as in univalves, or in union with one another, or others connected with a ligament, cartilage, hinge, teeth, or other fastening, is denominated a valve. The shells therefore, consisting of a single piece, are called univalves, those of two parts bivalves, and those of many parts multivalves. Between bivalve and multivalve no distinction is drawn, shells consisting of more than two such parts being called multivalve, without any regard to the number. Linnæus begins with the multivalves and the most complex structure, and ends with those of the simplest form. According to this naturalist the multivalves contain, the chiton, lepas, and pholas: the bivalves contain the mya, solen, tellina, cardium, mactra, donax, venus, spondylus, chama, arca, ostrea, anomia, mytillus, and pinna: and the univalves contain the argonauta, nautilus, conus, cyprœa, bulla, voluta, buccinum, strombus, murex, trochus, turbo, helix, nerita, paliotis, patella, dentalium, serpula, teredo, and sabella. See SHELL, TESTACEA.

CONCRETIONS, morbid, in animal economy, hard substances that occasionally make their appearance in different parts of the body, as well in the solids as in those cavities destined to contain fluids: in the first place they are denominated concretions or ossifications; in the other calculi. See BILIARY.

CONDUCTOR, in electricity, a term used to denote those substances which are capable of receiving and transmitting electricity, in opposition to electrics, in which the electric fluid may be excited or accumulated. See ELECTRICITY.

CONE, a kind of round pyramid, or solid body

having a circle for its base, and its sides are formed by right lines drawn from the circumference of the base to a point at top being the vertex or apex of the cone. Or a cone is a solid figure whose base is a circle, and which is produced by the entire revolution of a right angled triangle about its perpendicular leg. See MENSURATION.

CONFERVA, see BOTANY.

CONFESSION, in the Romish church, the act of acknowledging crimes and errors of conduct to a priest, in private, to the end that due reprehension may be suffered, and pardon obtained. By the canon-law, the priest who reveals what has been confessed to him, from anger, hatred, or even fear of death, is to be degraded.

CONFESSOR, an inferior saint of the Roman church; one who has resolutely stood forward to confess or avow his faith, and endured torture, if not martyrdom for its sake.

Confessor, a priest, in the Roman church, who has power to receive confessions and grant absolution.

CONGE d'elire, see Bishop.

CONGELATION, may be defined the transition of a liquid into a solid state, in consequence of an abstraction of heat: thus metals, oil, water, &c. are said to congeal when they pass from a fluid into a solid state. With regard to fluids, congelation and freezing mean the same thing. Water congeals at 32°, and there are few liquids that will not congeal, if the temperature be brought sufficiently low. The only difficulty is to obtain a temperature equal to the effect; hence it has been inferred that Quidity is the consequence of caloric. See FLUIDITY.