circular plate carrying verniers, telescopestandards, plate-level vials, and a magneticcompass. The spindle is accurately fitted tocoincide with the socket in the lower plate spindle.A clamp is tightened to hold the two platestogether or loosened to permit the upper plate torotate relative to the lower plate. A tangent screwpermits the upper plate to be moved a smallamount and is known as the UPPER MOTION.The standards support two pivots with adjustablebearings that hold the horizontal axis and permitthe telescope to move on a vertical plane. Thevertical circle moves with the telescope. A clampand tangent screw are provided to control thisvertical movement. The vernier for the verticalcircle is attached to the left standard. Thetelescope is an erecting type and magnifies theimage about 18 to 25 times. The reticle containsstadia hairs in addition to the cross hairs. Amagnetic compass is mounted on the upper platebetween the two standards and consists of amagnetized needle pivoted on a jeweled bearingat the center of a graduated circle. A means isprovided for lifting the needle off the pivot toprotect the bearing when the compass is not in use.LEVEL VIALS.— Two plate level vials (fig.11-6) are placed at right angles to each other. Onmany transits, one plate level vial is mounted onthe left side, attached to the standard, under theFigure 11-8.-Horizontal scales, 20 second transit.11-16
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business
