Compasses
An instrument for measuring figures, describing circles, etc., consisting of two pointed limbs usually pivoted together at the top. COMPENSATION The correction of the effect of variations of temperature on the vibrations of the balance or pendulum. The first person, says Nelthrop, who seems to have observed that metals changed their length, by changes of temperature, was Godfroi Wendelinus, Canon of Conde, in Flanders, about the year 1648. John Ellicott, a watchmaker of London, invented a pyrometer, for testing the expansions and contraction of metals, about 1740. About the year 1715, Graham endeavored to make a pendulum rod that should counteract the effect of heat and cold, but did not succeed. In 1722 he made a clock with a mercurial pendulum, or rather, instead of a metal bob he used a vase filled with mercury which he attached to the end of the rod, which proved quite successful and was the first attempt at compensation. In 1726, Harrison completed his gridiron pendulum, and there is little doubt that he was the first to apply compensation to the balance of a watch, which he did in 1749; but as there is no written evidence, the honor was claimed by F. Berthoud, who in 1766 made a watch with compensation balance, for Pinchbeck, a London watchmaker, for his majesty George III. Nelthrop thus describes it: The compensation piece was made of brass and steel pinned together; one end was fixed to the fore-plate, the other was made to act on a short arm projecting from a movable arbor; a longer arm, having the curb pins in it, moved nearly in the circle of the outer coil of the spiral spring. Mudge invented a compensation for heat and cold, which he applied to his time keepers. His system was more simple than that invented by Berthoud, but acted in the same manner on the spiral spring. He applied it in 1774 to a watch. Abraham Breguet invented and applied to his watches a V-shaped compensation curb, made to correspond in a great measure with the circumference of the balance. Nelthrop describes it as a curb being made of brass and steel, the brass being inside, and so arranged, by being screwed on to the extremity of the regulating index, that the balance-spring vibrated between one end of it, formed into a heel, and a fixed pin. The action was simple: in cold weather the space between the heel of the compensation curb and the pin, became enlarged, through the contraction of the compound laminae; consequently the balance-spring had more room to vibrate in. In warm weather the laminae expanded, thereby reducing the space, and contracting the expansion of the spring. The defect in this curb was the difficulty of adjustment, which caused it to be abandoned. Arnold also made experiments in order to try and obtain compensation and finally adopted a method entirely dissimilar to the others by placing the compensation in the balance alone. Arnold was followed by Earnshaw, who in 1802 invented a balance not unlike those in use today.