AN ORTHOSCOPE

(Gr. ayagflo?, and trxo^iu, I view.) The name given by M. Plateau, of Bru els, to an instrument invented by him, and intended to produce a peculiar kind of anamorphoses by means of two discs rotating rapidly one before the other, the hind one of which is transparent, and bears distorted figures, while the front one is opaque, and pierced with a small number of narrow slits. As in other toys of a similar kind, the Phenakistoscope, for example, the effect depends on the persistence of impre ions on the retina. The instrument is described at length in the London, Edinburgh, and Dublin Philosophical Magazine, Third Series, No. 245. — June, 1850. [s. 1365]