E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
We uncover the head when we wish to salute anyone with respect; but the Jews, Turks, Siamese, etc., uncover their feet. The reason is this: With us the chief act of investiture is crowning or placing a cap on the head; but in the East it is putting on the slippers. To take off our symbol of honour is to confess we are but the humble servant of the person whom we thus salute. (Bowing to rhyme with ploughing or plowing.)