In 1851 he published a Histoire des etas scandinaves, which is especially valuable for clear arrangement and for the trustworthiness of its facts.
The word was suggested by the Gr.)(etas, chaos, for he also writes: "I have called this spirit gas, it being scarcely distinguishable from the Chaos of the ancients" ("halitum illum Gas vocavi, non longe a Chao veterum secretum").
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