E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Spending ones time in learned trifles; darkening counsel by words; mystifying the more by attempting to unravel mysteries; putting truths into a lantern through which, at best, we see but darkly. When monks bring their hoods over their faces to meditate, they are said by the French to lanternise, because they look like the tops of lanterns; but the result of their meditations is that of a brown study, or fog of sleepy thought. (See above.)