White light, separated into the seven basic colours by means of a prism, can be recomposed in many ways by superimposing the beams thus obtained.
It is possible, for example, to use a second prism identical to the first but upside down, arranged so that its faces and its edge are parallel to those of the first; or one can use the system of the seven mirrors illustrated in the following article.
But to generate the sensation of white light in the eye, it is also possible to use devices which, by exploiting the phenomenon of the persistence of vision on the retina, allow the superimposition of the physiological effects of the seven basic colours.
Among these devices there is also the disk that has taken its name from Isaac Newton (1643-1727) which, in the exemplar conserved in the museum, consists of a vertical disk of sheet metal that can rotate around a horizontal axis passing through its centre.
There is a piece of white paper of the same size glued to the disk. The centre of the paper (diameter 8.5 cm) and a strip around at its edge (width 2.5 cm) are painted black. The remaining circular crown is divided into five equal sectors, each of which subdivided into seven others. Each of these sectors is painted with one of the seven basic colours in an attempt to produce five identical successions of seven colours as close as possible to the spectrum of solar light.
Daguin (1879), T. IV, p. 190
Drion - Fernet (1883), p. 714
Ganot (1864), p. 393
Violle (1892), T. II, p.te II, p. 488