HALO, n. Properly, a luminous ring encircling an astronomical body, bu… — The Devil's Dictionary
SAPIR 861
HALO, n. Properly, a luminous ring encircling an astronomical body, but not infrequently confounded with "aureola," or "nimbus," a somewhat similar phenomenon worn as a head-dress by divinities and saints. The halo is a purely optical illusion, produced by moisture in the air, in the manner of a rainbow; but the aureola is conferred as a sign of superior sanctity, in the same way as a bishop's mitre, or the Pope's tiara. In the painting of the Nativity, by Szedgkin, a pious artist of Pesth, not only do the Virgin and the Child wear the nimbus, but an ass nibbling hay from the sacred manger is similarly decorated and, to his lasting honor be it said, appears to bear his unaccustomed dignity with a truly saintly grace.
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