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hich does not meet the curve, but which possesses other properties of the polar. Thus the focus and directrix are pole and polar. There are also poles and polar curves to curves of higher degree than the second, and poles and polar planes to surfaces of the second degree.

oint in an orbit which is at either extremity of the latus rectum drawn through the empty focus of the orbit.

lated micrometer, a micrometer for an optical instrument, consisting of a reticule in the focus of an eyepiece. -- Reticulated work (Masonry), work constructed with diamond-shaped stones, or square stones placed diagonally.

A system of wires or lines in the focus of a telescope or other instrument; a reticle.

irdly, of a small lens, or magnifier, for throwing an enlarged image of the object at its focus upon a screen in a dark room or in a darkened box. -- Solar month. See under Month. -- Solar oil, a paraffin oil used an illuminant and lubricant. -- Solar phosphori (Physics), certain substances, as the diamond, siulphid…

A convex lens of glass for producing heat by converging the sun's rays into a focus. "Lighting a cigar with a sunglass." Hawthorne.

ngth that it may be used as an observing telescope for objects close at hand or as a long-focused microscope.

in equilibrium, the algebraic sum of their virtual moments is equal to zero. -- Virtual focus (Opt.), the point from which rays, having been rendered divergent by reflection of refraction, appear to issue; the point at which converging rays would meet if not reflected or refracted before they reach it. -- Virtual im…

vering an angle wider than the ordinary; -- applied to certain lenses of relatively short focus. Lenses for ordinary purposes have an angle of 50º or less. Wide-angle lenses may cover as much as 100º and are useful for photographing at short range, but the pictures appear distorted.