“To correct both of these conditions the rim of the balance wheel is made up of two different metals, the outer part brass, the inner part iron. When the hairspring becomes weaker by expansion the brass of the balance wheel also expands; but as it expands more than the iron to which it is bonded, it curls in toward the center of the wheel, making practically a wheel of smaller diameter, and causing the same effect as is produced when a clock pendulum is shortened. Exactly the opposite conditions obtain when the timepiece is exposed to extreme cold and the balance wheel has its diameter increased, thus causing a slowing up to counteract the increased strain produced by the contraction of the hairspring. The same principle is applied in the construction of first-class clocks. Any uncorrected variation in the length of a pendulum is fatal to the timekeeping quality of a clock. A gridiron pendulum made up of alternate rods of steel and brass serves to correct the result of the expansive force. “The central steel rod passes through holes in the lower horizontal framework and supports the bob at the lower end. The steel rods are so arranged that they will expand downward, while the brass rods expand upward and the total length of each metal used is exactly sufficient to counteract each other’s expansion, and the centre of the bob will remain at a constant distance from the point of suspension.” Scientific men and engineers are more or less familiar with the phenomena of expansion. But no inventor produced a system capable of utilizing this force to run a clock until Bangerter succeeded in mastering the problem. Bangerter’s clock is unquestionably a triumph of human ingenuity. It is a mechanical masterpiece. Herewith follows the complete specification: SPECIFICATION TO ALL WHOM IT MAY CONCERN: Be it known that I, FRIEDRICH BANGERTER, of the City of New York (Borough of Richmond), County of Richmond and State of New York, have invented certain new and useful improvements in APPARATUS FOR THE EDUCTION, STORAGE AND APPLICATION OF ENERGY FROM EXPANSIBLE MATERIALS, of which the following is a full, clear and exact specification, such as will enable others skilled in the art to which it appertains to make and use the same. This invention relates to apparatus whereby energy may be educed from expansible materials, due to the expansion and contraction thereof on changes of temperature, and the said energy either applied direct or stored and applied for the purpose of operating machines and devices of various kinds.