1. Discovery and early development of Invar

In the final years of the 19th century, steel had, with the occasional famous exception such as the Eiffel Tower, largely dethroned iron, and metallurgists were working to improve the strength/ductility compromise. To this end, they tried adding chromium and nickel, elements recently made available by geologists and chemists.

It was in this context that Commentry-Fourchambault-Decazeville developed, at its Imphy plant, the so-called "NC4" alloy containing 20-25% nickel and 2-3% chromium, recognized by the navy and artillery as an excellent armor material.

The Bureau International des Poids et Mesures (BIPM), created in 1875, was given the task of providing the signatory states of the Metre Convention with perfectly defined standards of length and mass.

Charles-Édouard Guillaume...