Several shortened names were soon suggested for the three emanations: "exradio", "exthorio", and "exactinio" in 1904; "radon" (Ro), "thoron" (To), and "akton" or "acton" (Ao) in 1918; "radeon", "thoreon", and "actineon" in 1919, and eventually "radon", "thoron", and "actinon" in 1920. (The name radon is not related to that of the Austrian mathematician Johann Radon.) The likeness of the spectra of these three gases with those of argon, krypton, and xenon, and their observed chemical inertia led Sir William Ramsay to suggest in 1904 that the "emanations" might contain a new element of the noble-gas family.