Clinometer (Gr. to incline, and
a measure), an instrument for measuring the angle made by any plane with the horizontal, and commonly used for determining the dip of beds of rock and the inclination of veins. It is made in various forms, as in that of a rule with a graduated arc upon the hinge to mark the angle of opening of the two arms. A spirit level attached to one arm serves to keep this in the horizontal plane, while the other is opened to coincide with the plane of the stratum of rock. Another convenient form is made by suspending a small metallic index upon the pivot of the needle of a pocket compass, which, by swinging freely, indicates the vertical line. The box is either square, or one side is furnished with a projecting limb, which forms a tangent to the circle at the zero point of the graduation. This tangent line being applied to a horizontal plane, the index marks zero; upon an inclined plane it marks the number of degrees this deviates from the horizontal. - In the French marine service, a clinometer is employed for determining the inclination of the keels of vessels at sea, in order to trim them for that draught of water fore and aft at which they are known to sail best.
The instrument adopted by the royal marine is that of M. Co-ninck, described in the Dictionnaire du commerce et des marchandises of M. Perpigna. It is made of two elongated glass bulbs, placed about 18 inches apart, and connected by a glass tube proceeding from their bases. Each bulb is half filled with mercury. From the upper extremity of each a tube proceeds, parallel with that at the base to within an inch of meeting, where they turn up in a vertical di-rection. To these vertical tubes is attached an index or vertical, which supports a scale of 2 degrees, divided into 120 minutes. Alcohol colored red is poured into the tubes until it fills them up to the point marked zero upon the scale. It rests upon the mercury, which transmits to the alcohol its oscillations. A bulb upon the summit of each of the tubes receives the alcohol when the violent movement of the ship causes it to flow over the open ends of the tubes. The angle of inclination being determined by the scale, and the length of the keel being known, the difference of draught at each extremity is easily calculated.