In Using this Form of Clinometer the prism is raised or lowered in its sliding fitting until the divisions of the card are sharply defined. Then in looking over the edge of the prism through the slot above it, the hair in the window of the back sight will appear to cut the divisions of the card; and the object seen in the distance, in front of the hair to which the instrument is directed, will appear coincident with the number of degrees of inclination indicated by the card.

This clinometer is sometimes fitted upon a prismatic compass, so that inclines may be read by the same prism and sight arrangement. This is, however, done more neatly by the arrangement next described, if the instrument is intended to be used with the prismatic compass only, and is not wanted separately for use with the chain.

609.—Barker's Combined Prismatic Compass and Clinometer,[36] Fig. 274.—The prismatic compass of this arrangement is that of Hutchison's form, art. 155. The clinometer is of the same kind as that just described, but this, instead of being a separate part of the instrument capable of detachment, remains permanent. To effect this arrangement the clinometer card is mounted over the compass card on a pin axis instead of centres. A part of the clinometer card is cut away so as to permit the compass card to be read beneath. This cut-away part is held by a stop to a position out of the field of the prism when the instrument is to be used as a prismatic compass. When the stop is released and the instrument is held with its face vertical, the pendulous clinometer card comes into view, and cuts by its reading through the prism the sight line, as before described for the prismatic clinometer. The prism is focussed to the upper or lower dial by a long, sliding fitting. It is used as the instrument last described.

610.—Continental Form of Clinometer.—Hand clinometers on the Continent are generally made on Captain Burnier's plan, Fig. 275, which was explained for the prismatic compass, art. 156. Indeed this instrument is more generally combined with the prismatic compass. The graduation is set up on a plated ring vertical to the plane of the swing of a pendulum, shown in section Fig. 276. The reading index is a hair which is read on the graduation by means of a cylindrical lens, B, when this is brought coincident with the sights D′W′ as described for Burnier's compass. When the clinometer and compass are combined the vertical rims stand opposite to each other, AC. A lifter, Fig. 275, L, is provided to take the working parts out of bearing, and a stop S′ to prevent oscillation. The illustrations show the combined instrument: B cylindrical lens reading the drums; A clinometer; C compass; DD′ fore sight; WW′ windows, both of which fold down on the top of the instrument.

611.—Major Watkins' Clinometer.[37]—The vertical plane of division is adopted, as in that of Captain Burnier, but the reading, instead of being taken on the exterior of the ring by a magnifier, which entails a projection, is placed on its interior. This reading is magnified by a concave reflector, shown Fig. 277 at R, which reads to a line on a slip of ivory placed just beside the eye-hole E shown in the engraving. The pendulum is stopped by a pin, upon which it springs when the box is rotated vertically to prevent wear when out of use. There is much less work in making this instrument than Burnier's, and the round form is more portable. The only point on which it does not bear comparison is in that the concave mirror represents a uniform distance sight which makes the reading indistinct to persons of weak sight, whereas Burnier's admits of adjustment by placing the instrument nearer to or further from the eye, the cylindrical lens being made large to admit of this form of adjustment. This instrument could be improved by the mirror being made adjustable. Weight, 6 oz.

612.—Clinometer Sights.—A clinometer sight is often attached to a light pocket compass, as shown Fig. 278 at the upper part of the engraving, consisting of a pin hole and hair cross. This, used in the manner shown by the position of the eye in the engraving, can only be made to take sight inclines by another person reading the pendulum index, which marks the inclination in the degrees to which the compass is divided. This portable pocket instrument is, however, useful in other ways. Standing face to the instrument it will measure inclines directly very fairly by looking over the top edge and bringing this to the visual rate of inclination at which the pendulum index can be read in front view. Geologists commonly use it in this way to take the dip of strata. It can also be used by putting it on or against any inclined surface. The case is generally gilt or nickel plated, and is about 2 inches diameter, and the instrument weighs about 3 oz.

613.—Rule Form Clinometer.—This is made in the form of a stout 12-inch, one-fold boxwood rule, Fig. 279. It is much used by civil engineers as a working tool, and intended to be applied directly to an inclined surface, either placed on a straight-edge or otherwise, generally to take the inclination of earth work. It may be placed upon a picket laid upon the ground to take natural slope. When used in this manner the lower surface is placed on the straight-edge or picket, and the rule is slowly opened until the bubble in the level in the upper limb becomes central. The arc of the head joint will then indicate the inclination. It may be used in another way: the lower limb may be set level on the dumpy level compass or on any flat plane, and the inclination may be sighted through the pin-hole and cross-hair sights shown at the ends of the upper part of the instrument. Its size is 6¾ by 1¾ by ½ inches; weight 9 oz. There are several varieties of this instrument.

614.—The Road Tracer is a balanced clinometer much used by natives in India and China for road making, Fig. 280. It consists of a pendulum, supported upon a stand that carries a sighted tube which indicates the level of the ground when the weight is carried in the axis of suspension. The weight is adjustable to a scale by a screw. The scales read inclines, by displacement of the weight, up and down in percentages or gradients, to which it may be divided.

This instrument has been improved by Mr. C. V. Bellamy, M.I.C.E., M.I.M.E., F.G.S., &c., Director of Public Works, Lagos, West Africa, a civil engineer who has had great experience in the colonies, and it will be found much more accurate, less liable to get out of order and far more convenient to use than the old forms. It is shown at Fig. 281.

The chief feature of this pattern lies in the adoption of the arc of a circle instead of a straight scale, and a pendulum weight actuated by a rack and pinion in place of the screw and sliding weight. This admits of greater nicety in the divisions and allows a stronger and lighter construction.

The sighting tube is provided with reversible sliding shutters, so that back readings may be taken without unclamping the instrument or altering the vernier or index. A powerful clamp is provided for locking at any desired grade.

A recent further improvement by Mr. Bellamy has been made by making this instrument in a form to give readings in degrees of arc as well as in gradients. Fig. 282.