Concerning the Face which Appears in the Orb Of the Moon (23)

There is this, however, I said, which seems to be a stronger objection to the alleged reflection from the moon. It happens that those who have placed themselves in the path of reflected rays see not only the object illuminated but also what illuminates it. For example, if when a ray of light rebounds from water to a wall the eye is situated in the place that is itself illuminated by the reflection, the eye discerns all three things, the reflected ray and the water that causes the reflection and the sun itself,[*] the source of the light which has been reflected by impinging upon the water. On the basis of these admitted and apparent facts those who maintain that the moon illuminates the earth with reflected light are bidden (by their adversaries)[*] to point out in the moon at night an appearance of the sun such as there is in water by day whenever there is a reflection of the sun from it. Since there is no such appearance, (these adversaries) think that the illumination comes about in another way and not by reflection and that, if there is not reflection, neither is the moon an earth. What response must be made to them then? said Apollonides, for the characteristics of reflection seem to present us with a problem in common. [*]

In common in a way certainly, said I, but in another way not in common either. In the first place consider the matter of the image,[*] how topsy-turvy and like rivers flowing uphill[*] they conceive it. The fact is that the water is on earth and below, and the moon above the earth and on high; and hence the angles produced by the reflected rays are the converse of each other, the one having its apex above at the moon, the other below at the earth.[*] So they must not demand that every kind of mirror or a mirror at every distance produce a similar reflection, since (in doing so) they are at variance with the manifest facts. Those, on the other hand, who declare that the moon is not a tenuous or a smooth body as water is but a heavy and earthy one,[*] I do not understand why it is required of them that the sun be manifest to vision in her. For milk does not return such mirrorings either or produce reflections of the visual ray, and the reason is the irregularity and roughness of its particles[*]; how in the world the is it possible for the moon to cast the visual ray back from herself in the way that the smoother mirrors do? Yet even these, of course, are occluded if a scratch or speck of dirt or roughness covers the point from which the visual ray is naturally reflected, and while the mirrors themselves are seen they do not return the customary reflection.[*] One who demands that the moon either reflect our vision from herself to the sun as well or else not reflect the sun from herself to us either is naive, for he is demanding that the eye be a sun, the vision light, and the human being a heaven. Since the light of the sun because of its intensity and brilliance arrives at the moon with a shock, it is reasonable that its reflection should reach to us; but the visual ray, since it is weak and tenuous and many times slighter, what wonder if it does not have an impact that produces recoil or if in rebounding it does not maintain its continuity but is dispersed and exhausted, not having light enough to keep it from being scattered about the irregularities and corrugations (of the moon)? From water, to be sure, and from mirrors of other kinds it is not impossible for the reflection (of the visual ray) to rebound to the sun, since it is still strong because it is near to its point of origin[*]; but from the moon, even if the visual rays do in some cases glance off, they will be weak and dim and prematurely exhausted because of the magnitude of the distance.[*] What is more too, whereas mirrors that are concave make the ray of light more intense after reflection than it was before so as often even to send off flames,[*] convex and spherical mirrors[*] by not exerting counterpressure upon it from all points [give it off] weak and faint. You observe, I presume, whenever two rainbows appear, as one cloud encloses another, that the encompassing rainbow produces colours that are faint and indistinct. The reason for this is that the outer cloud, being situated further off from the eye, returns a reflection that is not intense or strong.[*] Nay, what need of further arguments? When the light of the sun by being reflected from the moon loses all its heat[*] and of its brilliance there barely reaches us a slight and feeble remnant, is it really possible that of the visual ray travelling the same double-course[*] any fraction of a remnant should from the moon arrive at the sun? For my part, I think not; and do you too, I said, consider this. If the visual ray were affected in the same way by water and by the moon, the full moon ought to show such reflections of the earth and plants and human beings and stars as all other mirrors do; but, if there occur no reflections of the visual ray to these objects either because of the weakness of the ray or the ruggedness of the moon, let us not require that there be such reflection to the sun either.