COMPENSATION BALANCE—A balance corrected for errors caused by variations in temperature. The type in most general use was invented by Thomas Earnshaw in the second half of the 18th century. The double rim of this balance is constructed of brass and steel soldered together in the form of a cut ring, the brass on the outside. When heat, elongating the balance ring, causes it to vibrate more slowly, the brass, expanding more than the steel, bends the free ends of the cut rim toward the center, thus decreasing the diameter of the balance and quickening the vibration. On the other hand, when cold, contracting the ring tends to quicken the vibration of the balance, the contraction of the brass rim draws the free end outward, making the diameter larger and the vibration slower in consequence. The compensation balance is also made with brass as the inner metal and aluminum outside. COMPENSATION CURB—A laminated bar of brass and steel or aluminum and brass fixed at one end, the free end carrying the curb pins that regulate the length of the balance spring. Common in old watches but not now in use. COMPENSATION PENDULUM—A pendulum so constructed that the distance between the point of suspension and the center of oscillation remains constant in all temperatures. See: _Pendulum, Gridiron and Pendulum, Mercurial Compensation_. [Illustration] CONTRATE WHEEL—A wheel whose cogs are parallel to its axis and whose axis is at right angles to the axis of the wheel into which it gears. A crown wheel. CORROSION—The eating or wearing away of metals by slow degrees through chemical action. COUNTERSINK—To enlarge the outer end of a hole for the reception of the head of a screw, bolt, etc. The term is also applied to the tool with which the countersink is formed. COVENTRY—A municipal, county, and parliamentary borough of Warwickshire, England. One of the important watchmaking centers of Great Britain. CROWN WHEEL—A wheel whose teeth project at right angles to the plane of the wheel. A contrate wheel. The escape wheel of the verge escapement is an illustration. CRUTCH—A light rod in a clock descending from the pallet arbor and ending in a fork which embraces the pendulum rod. It transmits the motion of the pallet to the pendulum. CTESIBUS—A famous Greek mechanician who lived in Alexandria about 130 B. C. Although his was not the first clepsydra as is claimed by some it was an ingenious and interesting one. Believed to have first applied toothed wheels to clepsydrae about 140 B. C. CURB PINS—See _Banking Pins_. CUSIN, CHARLES—A watchmaker from Autun, Burgundy, who laid the foundation for the Swiss watch industry in Geneva in 1587. It grew very slowly at first—in 1687 having only one hundred watchmakers with three hundred assistants. In 1760 there were at Geneva eight hundred watchmakers with 5,000 to 6,000 assistants.