A treatise on land-surveying; comprising the theory developed from five elementary principles; and the practice with the chain alone, the compass, the transit, the theodolite, the plane table, &cIllustrated by four hundred engravings, and a magnetic chart . ghly understood, any new one willcause no difficulty. The figure of the Transit was drawn from one made by L. E. Gurley, of Troy, N. Y. to the latter of whom the Author is indebted forBome valuable information respecting the details of the instrument. The Theodolit3 is of the favorite English form. 216 TRA]\SIT MD THEODOLITE SURVEYIXG.
A treatise on land-surveying; comprising the theory developed from five elementary principles; and the practice with the chain alone, the compass, the transit, the theodolite, the plane table, &cIllustrated by four hundred engravings, and a magnetic chart . ghly understood, any new one willcause no difficulty. The figure of the Transit was drawn from one made by L. E. Gurley, of Troy, N. Y. to the latter of whom the Author is indebted forBome valuable information respecting the details of the instrument. The Theodolit3 is of the favorite English form. 216 TRA]\SIT MD THEODOLITE SURVEYIXG. [pakt iv as determined bj the bubbles iu the small spirit levels, B, B, ofwhich there are two at right angles to each other. In the figure of the Theodolite, the large level b, and the semi*circle NN are for the purposes of Levelhng, and of measurinoVertical angles. Thej will therefore not be described in this place. (328) As the value of either of these instruments dependagieatlj on the accurate fitting and bearings of the two concentricvertical axes, and as their connection ought to be thoroughly under-stood, a vertical section through the body of the instrument isgiven in Fig. 214, to half the real ^ize. The tapering spindle or Fig. 2] 4. Tr^. mverted frustum of a cone, marked AA, supports the upper plateBB, which carries the index, or Verniers, V, V, and the whole bearing of this plate is at C, C, on the top of the hollowinverted cone EE, in which the spindle turns freely, but interior position of the bearings preserves them from dustand injury. This hollow cone carries the lower or graduated plate,and it can itself turn around on the bearings D, D, carrying with itthe lower circle, and also the upper one and all above it. The Vernier scales V, V, are attached to the upper plate, butlie in the same plane as the divisions L, L, of the lower plate, (sokhat the two can be viewed together, without parallax,) and are tHAP. I.] The Instruments. 217 cov
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License: Licensed
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectsurveying, bookyear18
