Bimetallic Bar
   Today the bimetallic bar is at the heart of most thermostats, but in the 19th century it was used to demonstrate differences in the coefficient of thermal expansion. Two metal strips, of different material but of the same dimensions, were riveted together at room temperature. Cooling the combination would make it bend one way, and heating it in a flame curved it in the opposite direction. 

   The bimetallic bar below, at the United States Military Academy at West Point, is of the standard form. The demonstration apparatus at the right, at the Callan Museum at St. Patrick's College in Maynooth, County Kildare, Ireland, uses a U-shaped bimetallic strip. One end is fixed, and the free end drives a mechanism to drive the pointer across the scale. This device was made by Yeates and Son of Dublin.

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