A Treatise on Surveying, Comprising the Theory and the Practice Volume 1

A Treatise on Surveying, Comprising the Theory and the Practice Volume 1

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1897 edition. Excerpt: ...of the steeple (Fig. 239), and P' the pin; then the plane in which the telescope moves, seen edgewise, is S P'; and, after being turned around, the line of sight moves in the plane S P," as far to one side of the vertical plane S P as S P' was on the other side of it. Rectification. Since the second adjustment causes the line of sight to move in a plane perpendicular to the axis on which it turns, it will move in a vertical plane if that axis be horizontal. It can be made so by raising or lowering one end of the axis by means of a screw placed in the standard for that purpose. 325. Centering Eye-Piece. In some instruments, such as that of which a longitudinal section is shown on page 220, the inner end of the eye-piece may be moved so that the cross-hairs shall be seen precisely in the center of its field of view. This is done by means of four screws, arranged in pairs, like those of the cross-hair ring-screws, and capable of moving the eye.piece up and down, and to right or left, by loosening one and tightening the opposite one. Two of them are shown at A, A, in the figure, in which B, B, are two of the cross-hair screws. 326. Centering Object-Glass. In some instruments four screws, similarly arranged, two of which are shown at C, C, can move, in any direction, the inner end of the slide which carries the object glass. The necessity for such an arrangement arises from the impossibility of drawing a tube perfectly J" straight. Consequently, the line of collima Ijg tion, when the tube is drawn in, will not ' coincide with the same line when the tube is pushed out. If adjusted for one poeition, it will therefore be wrong for the other. These screws, however, can make it right in both positions. They are used as follows: Sight to some...show more

Product details

  • Paperback | 128 pages
  • 189 x 246 x 7mm | 240g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236490665
  • 9781236490667