I do set my bow in the cloud, and it shall be for a token of a covenant between me and the earth. I do set my bow in the cloud - On the origin and nature of the rainbow there had been a great variety of conjectures, till Anthony de Dominis, bishop of Spalatro, in a treatise of his published by Bartholus in 1611, partly suggested the true cause of this phenomenon, which was afterwards fully explained and demonstrated by Sir Isaac Newton. To enter into this subject here in detail would be improper; and therefore the less informed reader must have recourse to treatises on Optics for its full explanation. To readers in general it may be sufficient to say that the rainbow is a mere natural effect of a natural cause:
1. It is never seen but in showery weather.
2. Nor then unless the sun shines.
3. It never appears in any part of the heavens but in that opposite to the sun.
4. It never appears greater than a semicircle, but often much less.
5. It is always double, there being what is called the superior and inferior, or primary and secondary rainbow.
6. These bows exhibit the seven prismatic colors, red, orange, yellow, green, blue, indigo, and violet.
7. The whole of this phenomenon depends on the rays of the sun falling on spherical drops of water, and being in their passage through them, refracted and reflected.
The formation of the primary and secondary rainbow depends on the two following propositions;
1. When the sun shines on the drops of rain as they are falling, the rays that come from those drops to the eye of the spectator, after One reflection and Two refractions, produce the primary rainbow.
2. When the sun shines on the drops of rain as they are falling, the rays that come from those drops to the eye of the spectator after Two reflections and Two refractions, produce the secondary rainbow.
The illustration of these propositions must be sought in treatises on Optics, assisted by plates. From the well-known cause of this phenomenon It cannot be rationally supposed that there was no rainbow in the heavens before the time mentioned in the text, for as the rainbow is the natural effect of the sun's rays falling on drops of water, and of their being refracted and reflected by them, it must have appeared at different times from the creation of the sun and the atmosphere. Nor does the text intimate that the bow was now created for a sign to Noah and his posterity; but that what was formerly created, or rather that which was the necessary effect, in certain cases, of the creation of the sun and atmosphere, should now be considered by them as an unfailing token of their continual preservation from the waters of a deluge; therefore the text speaks of what had already been done, and not of what was now done, קשתי נתתי kashti nathatti, "My bow I have given, or put in the cloud;" as if he said: As surely as the rainbow is a necessary effect of sunshine in rain, and must continue such as long as the sun and atmosphere endure, so surely shall this earth be preserved from destruction by water; and its preservation shall be as necessary an effect of my promise as the rainbow is of the shining of the sun during a shower of rain.