7. BUT now it is evident, that all the drops of water found in any of the lines A ϰ, A λ, A μ, A ν, whether farther from the eye, or nearer than the drops B, C, D, E, F, will give the same colours as these do, all the drops upon each line giving the same colour; so that the light reflected from a number of these drops will become copious enough to be visible; whereas the reflection from one minute drop alone could not be perceived. But besides, it is farther manifest, that if the line A Ξ be drawn from the sun through the eye, that is, parallel to the lines M _n_, O _p_, Q _r_, S _t_, V _w_, and if drops of water are placed all round this line, the same colour will be exhibited by all the drops at the same distance from this line. Hence it follows, that when the sun is moderately elevated above the horizon, if it rains opposite to it, and the sun shines upon the drops as they fall, a spectator with his back turned to the sun must observe a coloured circular arch reaching to the horizon, being red without, next to that yellow, then green, blue, and on the inner edge violet; only this last colour appears faint by being diluted with the white light of the clouds, and from another cause to be mentioned hereafter[332]. 8. THUS is caused the interior or primary bow. The drops of rain at some distance without this bow will cause the exterior or secondary bow by two reflections of the sun’s light. Let these drops be G, H, I, K, L; X _y_, Z α, Γ β, Δ ι, Θ ζ denoting parcels of rays which enter each drop. Now it has been remarked, that these rays make with the visible refracted rays the greatest angle in those rays, which are most refrangible. Suppose therefore the visible refracted rays, which pass out from each drop after two reflections, and enter the eye in A, to intersect the incident rays in π, ρ, σ, τ, φ respectively. It is manifest, that the angle under Θ φ A is the greatest of all, next to that the angle under Δ τ A, the next in bigness will be the angle under Γ σ A, the next to this the angle under Z ρ A, and the least of all the angle under X π A. From the drop L therefore will come to the eye the violet-making, or most refrangible rays, from K the blue, from I the green, from H the yellow, and from G the red-making rays; and the like will happen to all the drops in the lines A π, A ρ, A τ, A φ, and also to all the drops at the same distances from the line A Ξ all round that line. Whence appears the reason of the secondary bow, which is seen without the other, having its colours in a contrary order, violet without and red within; though the colours are fainter than in the other bow, as being made by two reflections, and two refractions; whereas the other bow is made by two refractions, and one reflection only.