Page:Scientific Memoirs, Vol. 1 (1837).djvu/109

Rh by Newton around the point of contact of two slightly convex glasses or lenses. The order of the latter colours should therefore correspond exactly with that of my scale. It does so in fact; but that the correspondence may be perceived, it will be necessary first to rectify some errors which have arisen respecting the rings of Newton, either in consequence of their small dimensions, or of their having been examined under the influence of some prejudice.

Our scale embraces the extent of the first four rings, and consists, as we have already stated, of fourty-four tints.

It is well known that the colours of the thin layers around the point of contact of Newton's glasses are formed in the following manner. At the point which allows all the rays of the transmitted light to pass there appears a dark speck, and this remains the same whatever may be the quality of the light. If the incident light is white, the central speck is succeeded by several irises or concentric rings. If the light is homogeneous or produced by one species of rays, the irises are changed into rings of the same colour as the incident rays, and separated from each other by dark intervals. These rings, whatever be their colour, have their commencement all at the verge of the central speck, but they occupy different spaces. The violet rings are the narrowest and nearest; the red are the widest and most distant; the rings of the intermediate colours are of intermediate dimensions and at intermediate distances. When the incident light is white, the series of homogeneous rings are formed simultaneously and overlap each other; all the colours are intermixed in different proportions, and none stands isolated. It is to these combinations that we are to attribute the tints of the thin layers which we are about to analyse on our scale.

The Scale commences with the blond colour: of this there are four gradations, the first of which is silvery, and 2, 3, 4 are gradually deeper. The blond is succeeded by the tawny. Of this there are three species,