Save that an unknown element giving a group of four lines in the blue of the spectrum is concerned, we are still entirely ignorant of the nature of this substance.
Spectrum analysis of the black powder points unmistakably to the presence of an unknown element with a brilliant group of three lines in the green, and it is possible that it combines with argon to form a compound which acts at once with deadly effect upon some constituent in the blood.
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That a man pleasured could so easily resolve himself to the whole spectrum of acts, indifferent and murderous and humane, and choose with such arbitrary will what he shall have to remember forever and forever.
Chang-rae Lee -- A Gesture Life
His appreciation of growing things became more subtle, turned within a more limited spectrum and gradually Lalla’s visits tapered away.