Fig. 231.—Hanging clinometer.
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545.—A Light Hanging Clinometer, Fig. 231, shows the kind that is used in Germany, of 5 inches diameter, graduated to degrees, made of thin brass. It is packed in the case with the hanging compass, described art. 542. The ends of the semicircle are formed into hooks for hanging on the line. The plummet has a horse-hair line, which cuts the degrees. The clinometer may be used only when the hanging dial Fig. 230 cannot be suspended near the centre of the line, in which case this light semicircle will cause less deflection of the line, and give the inclination approximately. For further details of the use of the hanging compass the reader is referred to Mr. B. H. Brough's admirable work on Mine Surveying.
Fig. 232.—French semi-circumferentor.
Fig. 233.—Tripod head.
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546.—Semi-circumferentor.—This simple instrument can scarcely be enumerated with mining surveying instruments, as it is much more used for surface work; but being of the class of circumferentors to which miners' instruments generally belong, this is the most convenient place for its description. It has very general use on the Continent. Its construction is very simple, Fig. 232. It is supported on a ball and socket joint. The socket is formed in two pieces, which are clamped together to hold the ball by a winged-headed screw. One pair of sights is mounted upon the extreme ends of lugs upon the limb. The limb is divided to half degrees. When the ball is loosely clamped the fixed pair of sights may be adjusted to cut any desired object. A second pair of sights is jointed upon an axis to move centrally between the first pair. These are made shorter to pass within the first pair to any angle around the arc, except the small angles with which the sights themselves interfere when they are superimposed. The movable sights carry verniers to read on the limb to 2′. There is a small compass attached to the limb. As a cheap instrument for taking angles approximately it is very useful, particularly for workmen employed in carrying out work from drawings plotted from a survey by a better instrument. The weight of the instrument with 6-inch circle is about 2 lbs.; height above tripod, 7 inches.
547.—The tripod of this instrument is made of wood. The head is shown Fig. 233. The legs are simply extensions of the upper parts, which are shown attached with bolts. The point of each leg has a steel shoe to prevent it slipping in use. The head is turned to a cone, which fits into the socket-piece of the instrument and permits it to be rotated with moderate friction. The head is made of triangular section that the legs may be clamped firmly to it. When used for underground work a separate set of short legs is provided, which attach to the head by the same bolts.