Plaster model of Fresnel Wave Surface in three parts, by Delagrave, 1876.
© Science Museum / Science & Society Picture Library
Surface models were used to illustrate physical phenomena as well as purely mathematical concepts. August Fresnel (1788-1827) proposed his wave theory of light in the 1830s. The surface represents a wavefront of light radiating from a point in a crystal and consists of two shells which touch each other at four points.