Trilobite eyes were typically compound, with each lens being an elongated prism. The dual of a hexagonal prism is a hexagonal bipyramid. Bravais used an equilateral glass prism which he spun around its vertical axis. The dual of a pentagonal prism is a pentagonal bipyramid. The dual of a triangular prism is a triangular bipyramid. Thus the wave fronts will refract, changing direction like light passing through a prism. Furthermore, the state of elliptical polarization of the two paths through the prism is different. The basic 3-dimensional element are the tetrahedron, quadrilateral pyramid, triangular prism, and hexahedron. Beryl occurs in the shape of either a pebble or of an hexagonal prism. The final design depicts a glass prism dispersing light into colour. This is accomplished using a passive splitter prism inside each transceiver. It has a large viewfinder with interchangeable screens but a fixed prism. A relief panel depicts putti using instruments such as a telescope and prism. Newton's description of his experiments on prism dispersion was qualitative. In 1969 Paul produced the album Poe Through the Glass Prism for RCA.