Unpublished paper, 'On the dispursive [sic] powers of the ordinary and extraordinary spectra found by rock crystal and Iceland spar' by John I Cooper Cooper writes on dispersive spectroscopy using triangular prisms formed of rock crystal [quartz] and Iceland spar [calcite]. He sets out to show that the spectra formed by the double refraction of rock crystal and Iceland spar, which he refers to as ordinary and extraordinary spectra, differ from one another in their ability to disperse rays of light. Subject: Physics / Optics John George Children's initials appear next to the date received. Communicated by J G [John George] Children. Received by the Royal Society 7 June 1832. Written by Cooper in Lambeth [London]. 4 June 1832