. Deep borehole surveys and problems. Boring. PENDULUM METHODS 155 lamps i for illuminating the glass plate e, the index i and the plumb line g. There is also here a camera A; and a rolling film n driven by clockwork I and electrically controlled by the cable fine m. The frame d and glass plate e and the plumb line g can be placed at an angle in the tube a by means of the spring o on rod p and spring q bearing on plate c. The staple r is arranged to carry a lowering rope. If the apparatus is suspended by rod p the frame and springs will occupy the positions shown bold in Fig. 93, the springs b
. Deep borehole surveys and problems. Boring. PENDULUM METHODS 155 lamps i for illuminating the glass plate e, the index i and the plumb line g. There is also here a camera A; and a rolling film n driven by clockwork I and electrically controlled by the cable fine m. The frame d and glass plate e and the plumb line g can be placed at an angle in the tube a by means of the spring o on rod p and spring q bearing on plate c. The staple r is arranged to carry a lowering rope. If the apparatus is suspended by rod p the frame and springs will occupy the positions shown bold in Fig. 93, the springs being compressed and the rod / being parallel to the walls. If, however, the apparatus is suspended from the staple r the springs are released to the dotted position of Fig. 93, forcing the frame to the inclined position. To make a reading the appliance is suspended by rod p with two external points on its casing in the meridian. Then plumb fine g takes the position of the dip, and so the position of the dip of the borehole orifice is found. This position is photographed from below. Suspend the appli- ance on the staple r without turning and bring the plumb line spindle / into the inclined position. The plumb line g now assumes a position which is determined by the dip of the borehole and the inclined position of the axis/in accordance with the parallelo- gram of displacements. The film n is advanced by electrically releasing the clockwork I; the lamps j are again switched in and the new position of the plumb line recorded photographically. By compar- ing the two readings a diagram of the type shown in Fig. 94 is obtained, from which the deviation is found. The extent of the dip is calculated from the amount of deflection of the plumb line from the center of the scale on e and i and from the length of the plumb line itself. The distance of the bottom of the plumb line is read on a special scale on i. The objections to the apparatus are as follows: 1. Double suspension is liable
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