nebuliumn.
/nɛˈbjuːlɪəm/, U.S. /nɛbˈ(j)uliəm/ Astronomy. Now historical.
A hypothetical chemical element proposed to explain a set of green lines in the spectra of many gaseous nebulae (now attributed to forbidden transitions in nitrogen and oxygen ions). Frequently attributive, esp. in nebulium line.
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coronium1890
nebulium1898
1898 M. L. Huggins in Astrophysical Jrnl. 8 54 It would be a convenience if a name were chosen for the as yet undiscovered gas, which is suggested by the typical bright nebular lines as a principal constituent of the nebulæ. Sir William Huggins has occasionally used the term nebulum. Independently, Miss Agnes Clerke has made the suggestion to me of nebulium as an appropriate term.
1899 Atlantic Monthly Apr. 469 It is an impressive fact that hydrogen and nebulium are the only elements recognized in the nebulae.
1903 A. M. Clerke Probl. Astrophysics ii. xxviii. 517 The spectrum is purely gaseous, and is dominated visually, with more than the usual emphasis, by the green nebulium line.
1928 A. S. Eddington Stars & Atoms 55 A terrestrial atom will be stimulated to give nebulium light.
1937 J. W. T. Spinks tr. G. Herzberg Atomic Spectra iv. 157 Bowen..first showed that the nebulium lines..were to be explained as forbidden transitions between the deep terms of O+ (4S, 2D, 2P), O++ (3P, 1D, 1S), and N+ (3P, 1D, 1S).
1965 C. S. G. Phillips & R. J. P. Williams Inorg. Chem. I. ii. 43 Transitions between these states in atomic spectra are also ‘forbidden’, but they have been observed for the isoelectronic N+ and O2+ ions in the spectra of cosmic nebulae (so called nebulium lines).
1994 J. North Fontana Hist. Astron. & Cosmol. xv. 450 Huggins' pseudo-discovery of nebulium contrasts with the very real discovery of the element helium in the Sun by Norman Lockyer.
This entry has been updated (OED Third Edition, June 2003; most recently modified version published online March 2022).
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n.1898