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OBIT (through O. Fr., from Lat. obitu...

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Originally appearing in Volume V19, Page 948 of the 1911 Encyclopedia Britannica.
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OBIT (through O. Fr., from Lat. obitus, death, obire, to go down, to die), a term for death, formerly used for the account 2 The last history of Hugo of Toul (12th century) was the authority of Jacques de Guyse (14th century) in his Annales historiae princip. Hannoniae (Mon. Germ. xxx.), where there is an account (bk. ix. ch. 6) of Alberich. of any curvature to within an error of nth% of the radius: male and female templets being used for very deep curves, and the spherometer for tools of longer radii (by appropriate grinding together, the radii are alterable at will within narrow, but sufficient, limits). The accuracy attained in the grinding, however, is open to very perceptible modification by the subsequent polishing and figuring processes. This is particularly undesirable in the case of deep curves and large apertures. A variation in a radius of curvature may occasion a little spherical aberration at the axial focus, but if the amount be small it may be neutralized by imparting to the lens a parabolic form or its opposite. Such an artifice is frequently adopted in correcting large telescope objectives. With optical systems which transmit large pencils with considerable obliquity (such as wide angle photographic objectives) the curves are very deep, and a departure from the true radius which would be tolerated in a telescope cannot be permitted here. Such lenses are usually tested by means of a master curve worked in glass. The master curve is fitted to the experimental lens, and an inspection of the interference fringes shows the quality of the fit—whether it be perfect, or too shallow or too deep. The workman then modifies his polisher or stroke in order to correct the divergence. Flat surfaces are tested similarly. This test by contact has been strongly advocated and has been regarded as sufficient to detect all irregularities of any moment. This claim, however, is not justified, for the test is not sensitive to errors sufficient in amount to render a telescope objective almost valueless; but such errors are easily discernible by other optical devices. In general, accuracy in the radii of curvature is of primary importance and trueness of figuring is of secondary importance in photographic objectives, while the reverse holds with telescopic objectives; in wide angle microscopic objectives these two conditions are of equal moment. Eye pieces do not require the same degree of accuracy either of a person's death (now " obituary "). An " obit " was also a service performed at a funeral or in commemoration of a dead person, particularly the founder or benefactor of a church, college or other institution, hence "obit-days," "obit Sunday," &c. A "post-obit" is a bond given as a security for the repayment of money lent upon the death of a person from whom the borrower has expectations (see Boxn).
End of Article: OBIT (through O. Fr., from Lat. obitus, death, obire, to go down, to die)
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