Measuring instrument for the determination of variations of the gravitational acceleration

摘要

437,559. Measuring gravitational forces. THYSSEN - BORNEMISZA, STEPHAN, BARON VON, 126, Stadhouderslaan, Haag, Holland. Jan. 14, 1935, Nos. 1206, 1207, 1208, and 1209. Convention dates, Jan. 17, 1934, July 9, 1934, and Oct. 5, 1934. [Class 97 (iii)] Variations in gravitational force are measured by the consequent displacement of a mass connected to a lever system, the variations in position of which produce such variations in the lever arm with which the mass, a restraining spring, or an auxiliary mass acts that the displacement is amplified. The Figure shows the mass M suspended from a lever L secured to the base U by a blade spring E. When the force of gravity increases the inclination of the lever L increases until the spring E balances the combined action of the gravitational force and the increase of the lever arm L2. In a modification the spring E bends sufficiently to enable the lever L to be normally horizontal. A spirit or rolling-ball level is mounted on the lever L and is adapted to amplify any inclination arising from variations in gravitational force. In a further modification the mass is carried by a spring and is fixed to one end of a horizontal lever which rests at the other end on a support by means of a knife edge and carries an auxiliary mass at the end of an arm normally extending vertically above the knife edge. When the lever inclines due to variations in gravity the auxiliary mass assumes a leverage about the knife edge and increases the displacement. In a still further modification the lever has two arms at an angle and a knife edge support at the centre. The mass is secured to the end of the normally horizontal arm whilst a spring is secured to the inclined arm so that its leverage about the knife edge alters when the system is displaced slightly. In a further modification, a lever, centrally pivoted on a knife edge and having a mass fixed on one end and a vertical spring attached to the other carries on an axis slightly inclined to the vertical when the lever is horizontal an auxiliary pendulum which swings in a substantially horizontal plane through angles proportional to the tilting of the lever. In order to obviate the necessity for accurate levelling two instruments are arranged so that variations of inclination act on them in opposite sense and the mean reading is taken. In order to eliminate errors due to variations in temperature the coil springs are mounted in a tubular frame and the materials for the spring and frame are chosen so that the temperature coefficient of tension of the spring is equal but opposite in sign to the coefficient of thermal expansion of the frame. The springs may be of two parts having opposed twist.