Invar
Invar
Trademark name for an alloy of iron (64% iron, 36% nickel) that expands very little when heated. Invar was formerly used for absolute standards of length measurement and is now used for surveying tapes and in watches and various other temperature-sensitive devices. The name expresses the invariability of its dimensions. It was developed by Charles-Édouard Guillaume (1861–1938), winner of the 1920 Nobel Prize for Physics.
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