VITELLIO

, or Vitello, a Polish mathematician of the 13th century, as he flourished about 1254. We have of his a large Treatise on Optics, the best edition of which is that of 1572. Vitello was the first optical writer of any consequence among the modern Europeans. He collected all that was given by Euclid, Archimedes, Ptolomy, and Alhazen; though his work is of but little use now.

VITREOUS Humour, or Vitreus Humor, denotes the third or glassy humour of the eye; thus called from its resemblance to melted glass. It lies under the crystalline; by the impression of which, its forepart is rendered concave. It greatly exceeds in quantity both the aqueous and crystalline humours taken together, and consequently occupies much the greatest part of the cavity of the globe of the eye. Scheiner says, that the refractive power of this humour is a medium between those of the aqueous, which does not differ much from water, and of the crystalline, which is nearly the same with glass. Hawksbee makes its refractive power the same with that of water; and, according to Robertson, its specific gravity agrees nearly with that of water.