. Deep borehole surveys and problems. Boring. 166 DEEP BOREHOLE SURVEYS AND PROBLEMS 2. It is heavy and cumbersome and thus not suited for great depths. 3. It is not easy to manufacture and in some cases, , big deviations, will be difficult to manipulate. 4. It uses up more time than a lighter and simpler device. 5. It has too many movable parts. The Denis-Foraky Teleclinograph.—This is a pendulum apparatus and one of the best known of the modern precision devices employed in freezing shaft boreholes.^ It is remarkably accurate, being in many cases somewhat of the order 1 in 3,000.^ The pr
. Deep borehole surveys and problems. Boring. 166 DEEP BOREHOLE SURVEYS AND PROBLEMS 2. It is heavy and cumbersome and thus not suited for great depths. 3. It is not easy to manufacture and in some cases, , big deviations, will be difficult to manipulate. 4. It uses up more time than a lighter and simpler device. 5. It has too many movable parts. The Denis-Foraky Teleclinograph.—This is a pendulum apparatus and one of the best known of the modern precision devices employed in freezing shaft boreholes.^ It is remarkably accurate, being in many cases somewhat of the order 1 in 3,000.^ The principle is best understood as follows: Imagine a cylindrical tube (Fig. 102) of length AO with a system of rigidly orientated coordinates XF on one end when in situ in the hole. Knowing the coordinates of o' and the projection of A on the coordinate plane, we also get the position of the axis zz' of the tube which on a centered plumb is the hole axis also. Then by making a series of 10-m. interval observations we can get the borehole trace in 10-m. stretches projected on the horizon- tal plane. The freely oscillating pendulum A will, if given an initial impulse, describe a surface the trace of which on plane XY will be an ellipse with center o', which is the vertical projection of A. More correctly, but differing not sufficiently to affect the results with such small angles involved, it is the sphere to which the above plane is a tangent upon which the trace is generated. On the sphere parallels are traced to the axes XX' and YY' at a distance k and actually occupied by the conducting bars (reglets) on which the pendulum point contacts every time it crosses one, closing a circuit with a registering apparatus. ^ See a full description in Prospectus of Foraky, Societe anonyme d'entre- prise de forage et de foncage, Brussels. 2 Adam, D., Colliery Engineering, p. 414, Nov. 24, Fig. Please note that these images are extracted from scanned page images that may have bee
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