Rainbow (Heb. קֶשֶׁת, kesheth, i.e. a bow with which to shoot arrows, Ge 9:13-16; Ezekiel i, 28; Sept. τόξον, so Ecclesiasticus 43:11; Vulg. arcus. In the New Test. [Re 4:3; Re 10:11, ιρις), the token of the covenant which God made with Noah when he came forth from the ark that the waters should no more become a flood to destroy all flesh. With respect to the covenant itself, as a charter of natural blessings and mercies (" the world's covenant, not the Church's"), re-establishing the peace and order of physical nature, which in the flood had undergone so great a convulsion, see Davidson, On Prophecy, lect. iii, p. 76-80. With respect to the token of the covenant, the right interpretation of Ge 9:13 seems to be that God took the rainbow, which had hitherto been but a beautiful object shining in the heavens when the sun's rays fell on falling rain, and consecrated it as the sign of his love and the witness of his promise. The bow in the cloud, seen by every nation under heaven, is an un failing witness to the truth of God. Was the rainbow, then, we ask, never seen before the flood? Was this "sign in the heavens" beheld for the first time bv the eight dwellers in the ark when, after their long imprisonment, they stood again upon the green earth, and saw the clark, humid clouds spanned by its glorious arch? Such seems to be the meaning of the narrator. Yet this implies that there was no rain before the flood, and that the laws of nature were changed, at least in that part of the globe, by that event. There is no reason to suppose that in the world at large there has been such a change in meteorological phenomena as here implied. That a certain portion of the earth should never have been visited by rain is quite conceivable. Egypt, though not absolutely without rain, very rarely sees it. But the country of Noah and the ark was a mountainous country; and the ordinary atmospherical conditions must have been suspended, or a new law must have come into operation after the flood, if the rain then first fell, and if the rainbow had consequently never before been painted on the clouds. Hence, many writers have supposed that the meaning of the passage is, not that the rainbow now appeared for the first time, but that it was now for the first time invested with the sanctity of a sign; that not a new phenomenon was visible, but that a new meaning was given to a phenomenon already existing. The following passages, Nu 14:4; 1Sa 12:l0; 1Ki 2:35, are instances in which נָתִן, nathan, literally "give" — the word used in Ge 9:13, "I do set my bow in the cloud" — is employed in the sense off "constitute," "appoint." Accordingly there is no reason for concluding that ignorance of the natural cause of the rainbow occasioned the account given of its institution in the book of Genesis. SEE NOAH.
The rainbow is frequently seen in Palestine in the rainy season, and thus it furnishes a common image to the sacred writers. There is a reference to the rainbow, though not named, in Isa 54:10; and it is mentioned in other passages. "As the appearance of the bow which is in the cloud in the day of rain, so was the appearance of the brightness round about" (Eze 1:28). "And there was a rainbow round about the throne in sight like unto an emerald" (Re 4:3). "And I saw another mighty angel come down from heaven, clothed with a cloud, and a rainbow was upon his head" (Re 10:1). These three passages correspond with and reflect light upon each other. The rainbow in all of them is the designed token of God's covenant and mercy, and of his faithful remembrance of his promise. "Look upon the rainbow," says the son of Sirach (Ecclesiasticus 43:11, 12), "and praise him that made it: very beautiful it is in the brightness thereof; it compasseth the heaven about with a glorious circle, and the hands of the Most High have bended it." Among the Greeks and Romans, the personified rainbow, Iris, became the messenger of the gods, and the natural rainbow seems to have been conceived as the passage-way on which Iris came down to men (Serv. on Virgil's AEn. v, 610). The Indian mythology made a yet nearer approach to the Biblical view (Von Bohlen, India, i, 237); but the Edda represents the rainbow as a bridge connecting heaven and earth (see, in general, Menzel, Mythol. Forsch. p. 235 sq.). On the physical views of the ancients with regard to the rainbow. see Forbiger, Handb. d. alt. Geog. i, 596 sq. See Schlichter, Lie Iride ejusque Emblem. (Hal. 1739); Ausfeld, De Iride Diluvii non redituri Signo (Giess. 1756). SEE BOW.
Scientifically considered, the rainbow is a natural phenomenon which is formed by rays of light from the sun (occasionally the moon) striking drops of falling rain, being refracted in entering them, reflected back, in part, from the opposite side of the drops, and refracted again on leaving them, so as to produce prismatic colors, some of which meet the eye. In the inner or primary bow, the light is refracted downwards, and undergoes but one reflection; while in the outer or secondary bow the light, striking the lower side of the drop, is first refracted upwards, and reflected twice within the drop before leaving it; hence its light is fainter. Both present the colors of the prismatic spectrum; but in the primary bow the tints gradually ascend from the violet to the red, while in the outer the violet is more elevated. The colors of the rainbow are the result of the decomposition of white light in its passage through the globular drops of water forming a shower of rain.