In a paper on the Monochromatic Lamp, &c., read before this Society on the 15th April 1822, and published in their Transactions, I recorded some of my earliest experiments on the action of coloured media on the Solar Spectrum. These experiments were continued at irregular intervals, with the view of obtaining distinguishing characters of coloured media, of investigating the cause of the colours of natural bodies, and of examining more correctly the phenomena of the overlapping colours of equal refrangibility, the discovery of which I had announced in the paper already referred to. The results to which I was conducted on the two last of these subjects, have been already communicated to the Society in two papers, one on the Analysis of Solar light, and the other on the Colours of Natural Bodies.