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605.—Troughton's Abney's Clinometer.—In the Troughton form, Fig. 270, the arc is toothed, and it is moved by a pinion similar to the movement of the box sextant, so that the bubble moves slowly in relation to the motion of the fingers when adjusting. The arc is read by a single index line instead of by a vernier.
606.—Telescopic Hand Clinometer.—The author has recently added a telescope to the Abney form of clinometer, as shown Fig. 271. The arc is moved by rack and pinion and reads by a vernier to single minutes, therefore good reading within one minute of arc may be made with it. Captain East, R.E., suggested a mode of steadying the instrument for observation which appears to answer admirably for hand observation. He puts the hook-end of his walking-stick into his waistcoat pocket and clutches a part of the stick by his right hand at the height of his eye. Then holding the instrument in his right hand supported by the stick it is kept quite steady for observation.
Fig. 271.—Telescopic Abney clinometer.
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607.—De Lisle's Reflecting Clinometer.—There have been several arrangements made for converting the Burel level, [Fig. 89], into a clinometer; that devised by General A. De Lisle, R.E., with modifications by Colonel Bell and Mr. Alfred Cooke, as represented in Fig. 272, is the most popular. In this a heavy arc is constructed upon the lower part of the instrument. This is jointed upon a vertical axis at C so that it may be revolved to bring the mass of the arc either forward or backward, to take inclines upwards or downwards, or to rest at an intermediate position to make the instrument flat and portable in its case, it takes the position shown in the figure. The arc has a stiff centre axis with a radial bar, the edge of which forms the index. A sliding weight is placed on the radial bar, which is sufficiently heavy when at its greatest extension to exactly counterbalance the weight of the arc in a horizontal position and to make the mirror quite vertical. In this position it forms a simple Burel level. A set of graduations are made upon the arc, which are numbered 1 to 50 to 1 to 1. The radial bar index set to one of these numbers gives the amount of inclination that will result from the coincidence of the reflection of the centre of the pupil of the eye cutting the object to be observed. The length of this instrument is about 6 inches; its weight about 10 oz.
Fig. 272.—De Lisle's reflecting clinometer.
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