Polyhedron or polyscope, or faceted glass, as a term of optics, is a glass whose surface is composed of several flat surfaces, making different angles between them.

Polyhedral phenomena. If a series of rays such as EF, AB, CD, (Plates, Optics, Plate 6, Figure 71) are parallel on one surface of a polyhedron, they continue to be parallel after refraction. See Ray and Refraction.

Thus, if one assumes that the polyhedron is regular, the lines LH, HI, IM, will be tangent to one of the spherical convex lenses in F, B and D, and therefore, the rays which fall on the contact point, intersect the axis; this is why, since all other rays are parallel to them, they intersect; rays broken by the different faces will intersect one another at G.

Whence it follows that if the eye is placed at the point where the parallel rays cross one another, the rays of the same object will be assembled in as many different parts of the retina a, b, c, as the glass has faces.

Therefore the eye, through a polyhedron, sees objects repeated as many times as there are faces; and So, since the rays coming from distant objects are parallel; seen through a polyhedron, a distant object is as often repeated as the polyhedron has faces.

2. If the rays AB, AC, AD, (Figure 72) that come from a radiant point A, fall on different sides of a regular polyhedron, after refraction they intersect in G.

Whence it follows that if the eye is placed at the point where the rays, which come from different planes intersect, the rays will be assembled in as many different parts of the retina, b, c, as the glass has faces; therefore the eye being placed at the focal point, G, will even see a nearby object through the polyhedron, repeated as many times as the polyhedron has faces.

Thus, one can multiply the images of objects in a dark room, placing a polyhedron at its opening, and adding a convex lens at a suitable distance. See Camera obscura.

To make an anamorphic image, that is to say, a distorted image that seems regular and well made through a polyhedron or a glass which multiplies objects, at one end of a horizontal table to raise another one at right angles, where one could draw a figure; and On the other end raise another, which serves as a support, and which is mobile on the horizontal table: apply to the table, which serves as a support, a convex polyhedron consisting, for example of 24 plane triangles; add the polyhedron in a draw tube, that is, one that can lengthen and shorten; the end facing the eye must only have a very small opening, and be a little more distant than the focus. Move the supporting table away from the other perpendicular table, until it is out of the distance from the focus, and all the more so, that the image must be larger; in front of the small opening place a lamp; and on the vertical plane or draw with a lead black pencil the luminous disks coming out of the polyhedron faces.

In these disks, draw the different parts of an image in such a way that, joined together they make a whole, taking care to look from time to time to through the tube, to guide  and correct colors, and to see whether the various parties meet or match exactly.

Fill the remaining spaces with all kinds of figures or designs at will as you imagine, in such a manner that to the naked eye the whole thing offers very different appearance from what one proposes to represent with the polyhedron.

If one starts to look through the small opening of the tube again, one will see the different parts or different members, which are scattered in the disks, representing a continuous image; because all the intermediate objects totally disappear. See Anamorphosis. Wolf and Chambers.