Search the Dictionary

An attachment to a microscope, telescope, or other optical instrument, for making the image erect instead of inverted.

mor; o Retina; p Yellow spot; q Center of blind spot; r Artery of Retina in center of the Optic Nerve.

The lens, or combination of lenses, at the eye end of a telescope or other optical instrument, through which the image formed by the mirror or object glass is viewed. Collimating eyepiece. See under Collimate. -- Negative, or Huyghenian, eyepiece, an eyepiece consisting of two plano-convex lenses with their curved sur…

The space covered by an optical instrument at one view. Without covering, save yon field of stars. Shak. Ask of yonder argent fields above. Pope.

isting essentially of a silicate of lead and potassium. It is used for tableware, and for optical instruments, as prisms, its density giving a high degree of dispersive power; -- so called, because formerly the silica was obtained from pulverized flints. Called also crystal glass. Cf. Glass.

from the surface of the lens or mirror, or more exactly, in the case of a lens, from its optical center. --Focal distance of a telescope, the distance of the image of an object from the object glass.

bclasses of fishes. They have an arterial cone and bulb, spiral intestinal valve, and the optic nerves united by a chiasma. Many of the species are covered with bony plates, or with ganoid scales; others have cycloid scales.

An optical glass; a lens; a spyglass; -- in the plural, spectacles; as, a pair of glasses; he wears glasses.

An optical instrument for magnifying engravings, photographs, etc., usually having one large lens and two smaller ones.

The central chapel of the three forming the sanctuary of a Coptic church. It contains the high altar, and is usually closed by an embroidered curtain.

An oval lobe beneath each of the optic lobes in many fishes; one of the inferior lobes. Owen.

A condenser or reflector of light in optical apparatus; also, an illuminant.

the retinal blood vessels projected in, not merely on, that membrane. -- Virtual image (Optics), a point or system of points, on one side of a mirror or lens, which, if it existed, would emit the system of rays which actually exists on the other side of the mirror or lens. Clerk Maxwell.

Not active; inert; esp., not exhibiting any action or activity on polarized light; optically neutral; -- said of isomeric forms of certain substances, in distinction from other forms which are optically active; as, racemic acid is an inactive tartaric acid.

A variety of sugar, found in certain plants. It is optically inactive.

state of interfering, or of claiming a right to the same invention. Interference figures (Optics), the figures observed when certain sections of crystallized bodies are viewed in converging polarized light; thus, a section of a uniaxial crystal, cut normal to the vertical axis, shows a series of concentric colored ring…

g the same constitution (expressed by the name ethylidene lactic acid), but the latter is optically inactive, while sarcolactic acid rotates the plane of polarization to the right. The third acid, ethylene lactic acid, accompanies sarcolactic acid in the juice of flesh, and is optically inactive. -- Lactic ferment, an…

rved, or one curved and the other plane, and commonly used, either singly or combined, in optical instruments, for changing the direction of rays of light, and thus magnifying objects, or otherwise modifying vision. In practice, the curved surfaces are usually spherical, though rarely cylindrical, or of some other figu…

A neutral tint given to spectacles, shade glasses for optical instruments, etc., which reduces the intensity without materially changing the color of the transmitted light.

An optical device for making an indicator diagram for high- speed engines. It consists of a light-tight box or camera having at one end a small convex mirror which reflects a beam of light on to the ground glass or photographic plate at the other end. The mirror is pivoted so that it can be moved in one direction by a…