What is "cone of rays"

Cone \Cone\ (k[=o]n?), n. [L. conus cone (in sense 1), Gr. kw^nos; akin to Skr. [,c]ana whetstone, L. cuneus wedge, and prob. to E. hone. See Hone, n.]

1. (Geom.) A solid of the form described by the revolution of a right-angled triangle about one of the sides adjacent to the right angle; -- called also a right cone. More generally, any solid having a vertical point and bounded by a surface which is described by a straight line always passing through that vertical point; a solid having a circle for its base and tapering to a point or vertex.

2. Anything shaped more or less like a mathematical cone; as, a volcanic cone, a collection of scori[ae] around the crater of a volcano, usually heaped up in a conical form.

   Now had Night measured with her shadowy cone Half way up hill this vast sublunar vault.
   --Milton.

3. (Bot.) The fruit or strobile of the Conifer[ae], as of the pine, fir, cedar, and cypress. It is composed of woody scales, each one of which has one or two seeds at its base.

4. (Zo["o]l.) A shell of the genus Conus, having a conical form.

   Cone of rays (Opt.), the pencil of rays of light which proceed from a radiant point to a given surface, as that of a lens, or conversely.

   Cone pulley. See in the Vocabulary.

   Oblique cone or Scalene cone, a cone of which the axis is inclined to the plane of its base.

   Eight cone. See Cone, 1.