Invar is an alloy composed of 64% iron,
36% nickel, and a trace of carbon.
Having a very small coefficient
of linear expansion, invar is used for pendulums, tuning-forks, measuring
devices, and other components whose dimensions must be independent of temperature.
It was discovered by the Swiss physicist Charles Guillaume (1861–1938)
who was awarded the 1920 Nobel Prize in Physics for the discovery.