Keywords: history of technology historyoftechnology mining smithsonian probably public domain probablypublicdomain blackandwhite monochrome outdoor black and white SI Neg. CCC-2140. Date: 10/3/1921....Safety Switch.From the Consolidation Coal Company collection, National Museum of American History...Credit: unknown (Smithsonian Institution) SI Neg. CCC-2140. Date: 10/3/1921....Safety Switch.From the Consolidation Coal Company collection, National Museum of American History...Credit: unknown (Smithsonian Institution) |