5. OUR author delivers a method of finding each of these extream angles from the degree of refraction being given; by which method it appears, that the first of these angles is the less, and the latter the greater, by how much the refractive power of the drop, or the refrangibility of the rays is greater. And this last consideration fully compleats the doctrine of the rainbow, and shews, why the colours of each bow are ranged in the order wherein they are seen. 6. SUPPOSE A (in fig. 162.) to be the eye, B, C, D, E, F, drops of rain, M _n_, O _p_, Q _r_, S _t_, V _w_ parcels of rays of the sun, which entring the drops B, C, D, E, F after one reflection pass out to the eye in A. Now let M _n_ be produced to η till it meets with the emergent ray likewise produced, let O _p_ produced meet its emergent ray produced in ϰ, let Q _r_ meet its emergent ray in λ, let S _t_ meet its emergent ray in μ, and let V _w_ meet its emergent ray produced in ν. If the angle under M η A be that, which is derived from the refraction of the violet-making rays by the method we have here spoken of, it follows that the violet light will only enter the eye from the drop B, all the other coloured rays passing below it, that is, all those rays which are not scattered, but go out parallel so as to cause a sensation. For the angle, which these parallel emergent rays makes with the incident in the most refrangible or violet-making rays, being less than this angle in any other sort of rays, none of the rays which emerge parallel, except the violet-making, will enter the eye under the angle M η A, but the rest making with the incident ray M η a greater angle than this will pass below the eye. In like manner if the angle under O ϰ A agrees to the blue-making rays, the blue rays only shall enter the eye from the drop C, and all the other coloured rays will pass by the eye, the violet-coloured rays passing above, the other colours below. Farther, the angle Q λ A corresponding to the green-making rays, those only shall enter the eye from the drop D, the violet and blue-making rays passing above, and the other colours, that is the yellow and red, below. And if the angle S μ A answers to the refraction of the yellow-making rays, they only shall come to the eye from the drop E. And in the last place, if the angle V ν A belongs to the red-making and least refrangible rays, they only shall enter the eye from the drop F, all the other coloured rays passing above.