Scientific American 11, 5.12.1846
We have explained in a former number the refrangibility of light, and its decomposition thereby, in consequence of the difference of refrangibility of different colors. The phenomenon of the rainbow is never produced by a mere mist, but by falling drops of rain, each of which reflect different colors according to the angle which they form with the direction of the sun, and that of the eye of the beholder. In producing this effect, the ray of light in passing from the sun, is subjected in each individual rain-drop, to who refractions and one reflection, as illustrated in the diagram, in which A represents the rain drop, and S the direction of the sun. The ray encounters the drop at D, from which point it is refracted to N, whence it is reflected to Q, and thence refracted in different directions according to the different refrangibility of the various colors of which it is composed. We would not say that the representation in the cut is perfectly correct, because the decomposition of the ray must ecidently commence at the first point of refraction, D, though the divergence of the different colors from that point would be too mminute to be conveniently represented. From the position in which the eye is represented, the reflection of light from the rain-drop would appear red; but as the drop descends the apparent color changes to orange, yellow, green, blue, indigo and violet in succession; and the same effect being produced by a horizontal as well as a vertical obliquity, and the multiplicity of the drops and theis minute reflections being apparently blended, the phenomenon of the parti-colored arch is produced, as often seen in a retiring shower, or in the spray of a waterfall.