E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Mercury.
Images of Mercury, or rather, shapeless posts with a marble head of Mercury on them, used to be erected by the Greeks and Romans where two or more roads met, to point out the way. (Juvenal, viii. 53.)
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There are two famous statues of this god in Paris: one in the garden of Versailles, by Lerambert, and another in the Tuileries, by Mellana.
You cannot make a Mercury of every log. Pythagoras said: Non ex quovis ligno Mercurius fit. That is, Not every mind will answer equally well to be trained into a scholar. The proper wood for a statue of Mercury was boxwoodvel quod hominis pultorem pr se ferat, vel quod materies sit omnium maxime terna. (Erasmus.)