Definition of "nebulium" [nebulium]

• A supposed element proposed as a result of spectral analysis of light from a nebula; the emission lines concerned are now known to be due to doubly-ionized oxygen (noun)

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• "And what of that other unknown element we find glowing green in the far-flung nebulae — green as that we had just passed through — and that we call nebulium?"
• "And what of that other unknown element we find glowing green in the far-flung nebulae -- green as that we had just passed through -- and that we call nebulium?"
• "The gas "nebulium," not yet found on the earth, is the most characteristic constituent of irregular nebulæ."