*1. A piece of [[glass]], or other [[transparent]] substance, with two curved [[surfaces]], or one plane and one curved surface, serving to cause regular [[convergence]] or divergence of the [[rays]] of [[light]] passing through it. | *1. A piece of [[glass]], or other [[transparent]] substance, with two curved [[surfaces]], or one plane and one curved surface, serving to cause regular [[convergence]] or divergence of the [[rays]] of [[light]] passing through it. |