264 A New Form of Compass- Clinometer. 



a hole in its center, supports the axis, a, which carries the com- 

 pass-needle, b, and the clinometer pendulum, c. The other 

 glass plate, with the line d drawn on its surface, admits of be- 

 ing revolved around its center, in the same manner as the faces 

 of some aneroid barometers. The graduated circle, which 

 answers for both compass and clinometer index, is secured be- 

 tween the glass plates, as shown in the section. This circle is 

 divided from zero at the bottom, each way to ninety degrees, 

 and then from zero to ninety degrees again. Between the 

 ninety-degree points on each side, a cross-wire, e, is stretched, 

 which is horizontal when the instrument is held so that the 

 clinometer pendulum is at zero, and assists the eye in deter- 

 mining distant angles ; or a line may be drawn on the fixed 

 glass plate, which will answer the same purpose. 



When the instrument is held before the eye, with the pendu- 

 lum at zero, if the movable face is revolved so as to make the 

 line on the glass coincide with the sloping surface of a moun- 

 tain, for instance, the observer can at once read from the index 

 the angle which such an object forms with the horizontal line. 



When the inclination of a surface is required, the rod,/", is 

 drawn out, so as to make the base as long as possible, thus 

 securing greater accuracy, and the base of the instrument is 

 then applied to the inclined surface. The clinometer pendu- 

 lum will indicate the angle of dip. It is well to place a strip 

 of board on the sloping surface beneath the instrument, in 

 order to avoid errors arising from the unevenness of the rock- 

 surface. If this precaution were always taken, the extension- 

 rod in the base might be dispensed with. The bearings of 

 objects, the strike of out-crops, etc., are obtained in the usual 

 manner, with the aid of the magnetic needle. 



Although this form of clinometer is more accurate when of 

 large size, yet as a pocket-instrument, one of two and a-half 

 inches in diameter answers every purpose. I have found this 

 instrument of special service in measuring the dip of strata, 

 the edges of which are exposed in inaccessible cliffs. 



