. Encyclopaedia : or, A dictionary of arts, sciences, and miscellaneous literature; constructed on a plan, by which the different sciences and arts are digested into the form of distinct treatises of systems ... . revolution of the telefcope on its ax-is, they are eafi]y adjufted by means of the four fcrewsbbbb, placed on the telefcope about an inch from theend for the eye. Thefe fcrews act in perpendiculardirections to one another, by unferewing one and tight-ening the other oppofite to the wire, fo that if connect-ed with it, it may be moved either way at pleafure ;and in this manner the oth
. Encyclopaedia : or, A dictionary of arts, sciences, and miscellaneous literature; constructed on a plan, by which the different sciences and arts are digested into the form of distinct treatises of systems ... . revolution of the telefcope on its ax-is, they are eafi]y adjufted by means of the four fcrewsbbbb, placed on the telefcope about an inch from theend for the eye. Thefe fcrews act in perpendiculardirections to one another, by unferewing one and tight-ening the other oppofite to the wire, fo that if connect-ed with it, it may be moved either way at pleafure ;and in this manner the other wire perpendicular toit may be moved, and thus the interfection of thewires brought exactly in the axis of the tube. To the telefcope is fixed, by two fmall fcrews iecfthe level tube containing the fpirits, with a fmall bub-ble of air : This bubble of air, when the inftrumentis well adjufted, will fettle exactly in the fame place,in or near the middle of its tube, whether the te-lefcope be revcrfed or not on the fupporters, .which inthis cafe are kept unmoved. It is evident that the axis of the telefcope, or theinterfection of the wires as before fhown, muft be in this eafe Levels. Plate CCLZZ & />•<? ///•// r,/. Sciifo LEV I 9 ] L E v ?fctvtl. cafe truly level. In this facile mode of adjuftment agaio/r/tprecfiely while the telefcope is turned rouiid Levelling; ~~v con Sifts the new improvement of the inftrument; and on its Ys, it proves, as before mentioned, thai the axis *—-vr——. it is hereby capable of being adjufted by only one fta- of the telefcope coincides with the intersection of the tion and one object, which will at the fame time de- wires, and that the instrument will give the true level termine it to be in a true level. If by change of wea- direction. ther, accident, or otherwife, the inftrument mould The operation of levelling being of a very accurate have loll iis level adjuftinent or ftate, it may thus be and important nature, and the bell
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Keywords: ., bookauthoradamsjohn17351826formerownerbrl, bookauthorbostonpubl
