Ciências

Título: A national prototype kilogram standard mass, number K4, kept by the National Institute of Standards and Technology, USA, one of two which serve as the official standard for defining all units of weight and mass in the United States.

Data: 1915

Origem: National Geographic magazine, Vol. 27, No.1 (January 1915), p. 154, on Google Books. Photo credited to US National Bureau of Standards, now National Institute of Standards and Technology, Permissão: Original work of the US federal government

Fonte: https://pt.m.wikipedia.org/wiki/Ficheiro:Standard_kilogram,_2.jpg

Licença: Domínio Público