VII
1
2
As you have mentioned glass, some one interposes, I can draw from this same material an argument to confute you. Glass sticks are manufactured, either fluted or bulging,29 with many corners like a club. If one of these sticks is placed obliquely in the path of the sun’s rays, it sends back the colour which is wont to be seen in the rainbow. This proves that there is not here an image of the sun, but an imitation of his colour from reflection. Now, in this argument there are many points that make for my view. First of all, it is plain that there must be some smooth surface like a mirror to reflect the sun. Secondly, it is plain that no colour is formed in the rod, but only a false appearance of colour, such as I mentioned above, which the neck of a pigeon, as it is bent hither and thither, alternately puts on and off. This, I say, is seen likewise in the case of a mirror, which assumes no real colour, but only a certain imitation of the colour of a foreign body.
3
Still, this one point requires explanation; it is not the sun’s image that is beheld in that glass stick, because it is not capable of expressing it accurately. True enough it tries to reproduce the image, because the material is smooth and suitable for this purpose. But it fails because its shape is unsymmetrical. If it had been suitably constructed, it would reflect as many images of the sun as it had faces. But since the sides are not distinctly separated from each other, and not bright enough to serve as mirrors, the images are only incipient, not fully expressed; they get confused through being crowded together, and are reduced to the appearance of a single band of colour.