Meggers holding a mercury-vapor (Hg) lamp. (Inset) Recorded spectrum of 198Hg by Alvarez and Wiens, published in 1940 Physical Review. [NBS Archives, courtesy AIP Emilio Segrè Visual Archives, W.F. Meggers Collection / Inset from J. Wiens and L.W. Alvarez, Phys. Review 58(11), 1005, 1940. ©1940 by the American Physical Society]