Chemical element of metals. Cu comes from Cuprum, Fe comes from Ferrum, Ag from Argentum. The symbols were not followed by a period (full stop) as with abbreviations. Later chemical elements were also assigned unique chemical symbols, based on the name of the element, but not necessarily in English. For example, sodium has the chemical symbol 'Na' after the Latin "natrium". The same applies to "W" (wolfram) for tungsten, "Fe" (ferrum) for iron, "Hg" (hydrargyrum) for mercury, "Sn" (stannum) for tin, "K" (kalium) for potassium, "Au" (aurum) for gold, "Ag" (argentum) for silver, "Pb" (plumbum) for lead, "Cu" (cuprum) for copper, and
The Silver Branch (Sutcliff novel) himself Carausius's hound and who wears a dog's tail as part of his motley. Subtle allusions to the silver branch recur in other novels in the Eagle of the Ninth series, and it presumably refers to the otherworldly musical instrument mentioned in the medieval Irish narrative The Voyage of Bran. The Silver Branch was also a symbol of authority and a temporary "pass card" used by the Celts, consisting of a sprig of mistletoe or an apple branch. "The Silver Branch" is #2 in the Roman Britain Series, following "The Eagle of the Ninth" (1954) and preceding "Frontier Wolf" (1980),