A. Flat bimetal will be examined to explain the working. If a flame is held under the bimetal, the nickel will expand more than the invar, with the result that the free end moves down. If the bimetal is allowed to cool, it will slowly straighten. This can be constructed so that the free end of the bimetal operates an electric switch, completing the theemostat. Figs. 10a and show a simple construction of a thermostat.