Part 95

INCIDENCE. The direction in which a body, or a ray of light, moves in its approach towards any substance, upon which it strikes.

INCLINED PLANE. One of the six mechanical powers. Any plane surface inclined to the horizon, may be so denominated.

INERTIA. One of the inherent properties of matter. Want of power, or of any active principle within itself, by which it can change its own state, whether of motion, or of rest.

INHERENT PROPERTIES. Those properties which are absolutely necessary to the existence of a body; called also essential properties. All others are denominated accidental. Colour is an accidental--extension, an essential property of matter.

LATITUDE. Distance from the equator, in a direct line towards either pole. This distance is measured in degrees and minutes. The degree of latitude cannot exceed ninety, or one quarter of a circle. Places to the south of the equator, are in south latitude, and those to the north, in north latitude.

LATITUDE, PARALLELS OF. Lines drawn upon the globe, parallel to the equator, are so called; every place situated on such a line, has the same latitude, because equally distant from the equator.

LENS. A glass, ground so that one or both surfaces form segments of a sphere, serving either to magnify, or diminish objects seen through them. Glasses used in spectacles are lenses.

LEVER. One of the mechanical powers. An inflexible bar of wood or metal, supported by a fulcrum, or prop; and employed to increase the effect of a given power.

LIBRA. One of the twelve signs of the zodiac. That into which the sun enters, at the autumnal equinox.

LIGHT. That principle, by the aid of which we are able to discern all visible objects. It is generally believed to be a substance emitted by luminous bodies, and, exciting vision by passing into the eye.

LONGITUDE. Distance measured in degrees and minutes, either in an eastern, or a western direction, from any given point either on the equator, or on a parallel of latitude. Degrees of longitude may amount to 180, or half a circle. A degree of longitude measured upon the equator, is of the same length with a degree of latitude; but as the poles are approached, the degrees of longitude diminish in length, because the circles upon which they are measured, become less.

LUNAR. Relating to Luna, the moon.

LUNATION. The time in which the moon completes its circuit. A lunar month.

LUMINOUS BODIES. Those which emit light from their own substance; not shining by borrowed, or reflected light.

MACHINE. Any instrument, either simple or compound, by which any mechanical effect is produced. A needle, and a clock, are both machines.

MAGIC LANTHORN, OR LANTERN. An optical instrument, by which transparent pictures, painted upon glass, are magnified and exhibited on a white wall or screen, in a darkened room. The phantasmagoria, is a species of magic lanthorn.

MATHEMATICS. The science of numbers and of extension. Common arithmetic, is a lower branch of the mathematics. In its higher departments, it extends to every thing which is capable of being either numbered or measured.

MATTER. Substance. Every thing with which we become acquainted by the aid of the senses; every thing however large, or however minute, which has length, breadth, and thickness.

MECHANICS. That science which investigates the principles, upon which the action of every machine depends; and teaches their proper application in overcoming resistance, and in producing motion, in all the useful purposes to which they are applied.

MEDIUM. In optics, is any body which transmits light. Air, water, glass, and all other transparent bodies, are media. Medium also denotes that in which any body moves. Air is the medium which conveys sound, and which enables birds to fly.

MELODY. A succession of such single musical sounds, as form a simple air or tune.

MERCURY. That planet which is nearest to the sun. Quicksilver, a metal, which remains fluid at the common temperature of the atmosphere. It is capable of being rendered solid, by intense cold.

MERIDIAN. Midday. A meridian line, is one which extends directly from one pole of the earth to the other; crossing the equator at right angles. It is therefore half of a great circle. The hour of the day is the same at every place situated on the same meridian. Longitude is measured from any given meridian, to the opposite meridian. Places at the same distance in degrees, to the east or west of any meridian, have the same longitude.

MICROSCOPE. An optical instrument, by which minute objects, are magnified, so as to enable us to perceive and examine such as could not be seen by the naked eye.

MINERAL. Earths, stones, metals, salts, and in general all substances dug out of the earth, are denominated minerals.

MINUTE. In time, the sixtieth part of an hour. In length, the sixtieth part of a degree. A minute of time, is an unvarying period; but a minute in length varies in extent, with the degree of which it forms a part. The degrees and minutes are equal in number, upon a common ring, upon the equator of the earth, or, on any circle of the heavens.

MIRRORS. Polished surfaces of metal, or of glass coated with metal, for the purpose of reflecting the rays of light, and the images of objects. Common looking-glasses, are mirrors. Those used in reflecting telescopes, are made of metal.

MOBILITY. Capable of being moved from one place to another. This is accounted one of the essential properties of matter, because we cannot conceive of its existence without this capacity.