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An optical apparatus in which pictures are viewed through a large lens with stereoptical effects. It is often combined with the stereoscope.

ined by the number of screw revolutions necessary to bring the points to be measured into optical coincidence. When the two images are formed by a bisected objects glass, it is called a divided-object-glass micrometer, and when the instrument is large and equatorially mounted, it is known as a heliometer. -- Double re…

An optical instrument, consisting of a lens, or combination of lenses, for making an enlarged image of an object which is too minute to be viewed by the naked eye. Compound microscope, an instrument consisting of a combination of lenses such that the image formed by the lens or set of lenses nearest the object (called…

An optical effect, sometimes seen on the ocean, but more frequently in deserts, due to total reflection of light at the surface common to two strata of air differently heated. The reflected image is seen, commonly in an inverted position, while the real object may or may not be in sight. When the surface is horizontal,…

a lamp whose flame yields rays of some one homogenous light. It is of great importance in optical experiments.

An optical phenomenon sometimes seen on the summit of mountains (as on the Brocken) when the observer is between the sun and a mass of cloud. The figures of the observer and surrounding objects are seen projected on the cloud, greatly enlarged and often encircled by rainbow colors.

cture represented in slightly changed positions, producing, by persistence of vision, the optical effect of a continuous picture in which the objects move in some manner, as that of some original scene. The usual form of moving pictures is that produced by the cinematograph.

terior of the four lobes on the dorsal side of the midbrain of most mammals; the anterior optic lobes.

Of or pertaining to the eye; optic.

Of or pertaining to the eye; ocular; optic; as, oculary medicines. Holland.

The cavity of one of the optic lobes of the brain in many animals. B. G. Wilder.

y body when in the horizon, or the angle subtended at the body by the earth's radius. -- Optical parallax, the apparent displacement in position undergone by an object when viewed by either eye singly. Brande & C. -- Parallax of the cross wires (of an optical instrument), their apparent displacement when the eye chan…

Transparent and colorless rock crystal; as, Brazilian pebble; -- so called by opticians. Pebble powder, slow-burning gunpowder, in large cubical grains. -- Scotch pebble, varieties of quartz, as agate, chalcedony, etc., obtained from cavities in amygdaloid.

Of or pertaining to the science of vision; optical. [Obs.] Bacon.

Optically; as through a glass. [R.] You see them perspectively. Shak.

An optical glass; a telescope. [Obs.] Crashaw.

An optical instrument or toy, resembling the phenakistoscope, and illustrating the same principle; -- called also phantasmascope.

he mind, and supposed to be real or material; a shadowy or airy appearance; sometimes, an optical illusion; a phantom; a dream. They be but phantasms or apparitions. Sir W. Raleigh.

An optical effect produced by a magic lantern. The figures are painted in transparent colors, and all the rest of the glass is opaque black. The screen is between the spectators and the instrument, and the figures are often made to appear as in motion, or to merge into one another.

An instrument for studying the motions of sounding bodies by optical means. It consists of a tube across the end of which is stretched a film of soap solution thin enough to give colored bands, the form and position of which are affected by sonorous vibrations.