Dictionary of Physics or an Attempt at an Explanation of the Most Important Concepts and Technical Terms of Natural Philosophy

frangibilitatem lucis refrangibility of light, Aberration de refrangibilité. This deviation arises from the fact that, according to Newton's discovery, light rays are separated during refraction and dispersed into rays of different colors, of which some suffer stronger and others weaker refraction. See Refrangibility, Dispersion of colors. Therefore, among the rays emanating from a point, some are united closer to the glass and others further behind it, and as many images of the object are created as the light contains colors. The image created by the blue or violet rays stands closest to the glass, as at B in Plate 1, Fig. 6; that formed by the red rays is furthest away, at R. The distance BR between both, when the rays fall near the axis DC, amounts to approximately 1/10 of BC, otherwise even more. In the experiments conducted in Paris in the year 1774 with a hollow lens filled with spirits of wine, of which only a 6–7 line wide ring at the edge was left open (see Burning glass), Brisson (Mem. de Paris 1774) found the distance of the convergence point of the sun's rays from the center of the lens:

where BR amounts to 9 inches 7 lines, or 1/12 of BC.

Since the rays coming from a point cross each other in the manner clearly represented in the figure, no clear image of the radiating point can be created either at B or R themselves, nor anywhere between these points. At B, for example, the clear image created by the blue rays will be surrounded by light of other colors, and at the edge by red light from the very same point of the object; therefore, this deviation gives the image both false colors and colored edges.