E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
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.)
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.)