Search the Dictionary

A condition of the eye in which, through shortness of the eyeball or fault of the refractive media, the rays of light come to a focus behind the retina; farsightedness; -- called also hyperopia. Cf. Emmetropia.

ed in Iceland. It is used for the prisms of the polariscope, because of its strong double refraction. Cf. Calcite.

of a lens or mirror, by rays of light from the several points of the object symmetrically refracted or reflected to corresponding points in such focus; this may be received on a screen, a photographic plate, or the retina of the eye, and viewed directly by the eye, or with an eyeglass, as in the telescope and microscop…

or heat, falls on any surface. In equal incidences there is a considerable inequality of refractions. Sir I. Newton. Angle of incidence, the angle which a ray of light, or the line of incidence of a body, falling on any surface, makes with a perpendicular to that surface; also formerly, the complement of this angle.…

integral figures in the given number. It is also called the characteristic. -- Index of refraction, or Refractive index (Opt.), the number which expresses the ratio of the sine of the angle of incidence to the sine of the angle of refraction. Thus the index of refraction for sulphur is 2, because, when light passes o…

; to incline, to deflect; to curve; to bow. Are they [the rays of the sun] not reflected, refracted, and inflected by one and the same principle Sir I. Newton.

nces, or displacements by means of the interference of two beams of light; -- called also refractometer.

r directed; indisposed to be taught, disciplined, or tamed; violent; stubborn; obstinate; refractory; as, an intractable child.

Not refrangible; that can not be refracted in passing from one medium to another. -- Ir`re*fran"gi*ble*ness, n.

r future. (b) (Navigation) Tables for correcting an observed lunar distance on account of refraction and parallax. -- Lunar year, the period of twelve lunar months, or 354 days, 8 hours, 48 minutes, and 34.38 seconds.

the instrument is large and equatorially mounted, it is known as a heliometer. -- Double refraction micrometer, a species of double image micrometer, in which the two images are formed by the double refraction of rock crystal. -- Filar, or Bifilar, micrometer. See under Bifilar. -- Micrometer caliper or gauge (Mech.…

tomaine) formed in the decomposition of protagon with boiling baryta water, and in the putrefraction of proteid matter. It was for a long time considered identical with choline, a crystalline body originally obtained from bile. Chemically, however, choline is oxyethyl-trimethyl-ammonium hydroxide, while neurine is viny…

rection of the optic axis that objects are most distinctly seen. (b) The line in a doubly refracting crystal, in the direction of which no double refraction occurs. A uniaxial crystal has one such line, a biaxial crystal has two. -- Optical circle (Opt.), a graduated circle used for the measurement of angles in optica…

ded circular polarization of light. -- Optically positive, Optically negative. See under Refraction.

employment of subjective and objective mechanical means to determine the accomodative and refractive states of the eye and the scope of its function in general."

A highly refractive vitreous composition, variously colored, used in making imitations of precious stones or gems. See Strass.

Obstinate; willful; refractory. [Obs.] -- Per`vi*ca"cious*ly, adv. -- Per`vi*ca"cious*ness, n. [Obs.]

re referred for the purpose of determining their relative position in space. -- Plane of refraction or reflection (Opt.), the plane in which lie both the incident ray and the refracted or reflected ray.

It is usually a reflecting plate, or a plate of some crystal, as tourmaline, or a doubly refracting crystal.

gative, and said of metals, bases, and basic radicals. Positive crystals (Opt.), a doubly refracting crystal in which the index of refraction for the extraordinary ray is greater than for the ordinary ray, and the former is refracted nearer to the axis than the latter, as quartz and ice; -- opposed to negative crystal,…