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. ...continues