XIV. An account of experiments to determine the acceleration of the pendulum in different latitudes

Abstract

The clocks and pendulums used in these experiments are the property of the Royal Society, and were prepared by their direction under the immediate superintendance of Cap­tain Kater; who, in a manuscript account presented to the Society, of the instruments furnished to the Expeditions on Northern discoverv, has described them as follows: “The clocks were made by Shelton, and are the same which accompanied Captain Cook round the world: for each clock a pendulum was cast in one piece of solid brass: this was furnished with a knife edge of hard steel perfectly strait, and finished by drawing the edge longitudinally two or three times. on a soft hone, so as to take from its sharpness, and thus preclude any alteration from wear; the back of the knife edge bore firmly against a stout cross piece, and the heads of the screws securing it, were sunk below the surface, and concealed by brass pins, to prevent their being removed: the knife edge was carefully adjusted, so as to be at right angles to the direction of gravity: a very firm support of brass was screwed to the thick plank which forms the back of the clock case; in this were imbedded two pieces of agate, which were ground into portions of hollow cylinders, finished in their places to receive the knife edge of the pen­dulum: parallel to the agates a small level was fixed in the direction of the cylinders, by means of which they could be placed truly horizontal: an arc divided into degrees and tenths, but which might be read off by estimation to hundredths, was attached to the back of the clock case at the bottom of the pendulum, to give the arc of vibration.