“ King was recognized universally as one of the greatest authorities in this department of art. His chief works on the subject are: Antique Gems, their Origin, Uses and Value (1860) , a complete and exhaustive treatise; The Gnostics and their Remains (2nd ed. by J. Jacobs, 1887, which led to an animated correspondence in the Athenaeum) ; The Natural History of Precious Stones and Gems and of the Precious Metals (1865) ; The Handbook of Engraved Gems (2nd ed., 1885) ; Early Christian Numismatics (1873) . ”