Of the Face Appearing Within the Orb Of the Moon (16-20)

Sylla then, taking up the discourse, said: There is indeed a great deal of probability in all that you have spoken. But as to the strongest objection that is brought against it, has it, think you, been any way weakened by this discourse? Or has our friend quite passed it over in silence?

What opposition do you mean, said Lucius? Is it the difficulty about the moon, when one half of her appears enlightened?

The very same, answered Sylla. For there is some reason, seeing that all reflection is made by equal angles, that when the half-moon is in the midst of heaven, the light proceeding from her should not be carried upon the earth, but glance and fall beyond and on one side of it. For the sun, being placed in the horizon, touches the moon with its beams; which, being equally reflected, will therefore

And yet, by Jupiter, replied Lucius, this has not been forgotten or overpassed, but already spoken to. And casting his eye, as he was discoursing, upon the mathematician Menelaus; I am ashamed, said he, in your presence, dear Menelaus, to attempt the subverting and overthrowing of a mathematical position, which is supposed as a basis and foundation to the doctrine of the catoptrics concerning the causes and reasons of mirrors. And yet of necessity I must. For it neither appears of itself nor is confessed as true, that all reflections are at equal angles; but this position is first checked and contradicted in concave mirrors, when they represent the images of things, appearing at one point of sight, greater than the things themselves. And it is also disproved by double mirrors, which being inclined or turned one towards the other, so that an angle is made within, each of the glasses or plain superficies yields a double resemblance; so that there are four images from the same face, two answerable to the object without on the left side, and two others obscure and not so evident on the right side in the bottom of the mirror. Of which Plato renders the efficient cause; for he says, that a mirror being raised on the one and the other side, the sight varies the reflection, falling from one side to the other. And therefore, since of the views or visions some immediately have recourse to us, and others, sliding to opposite parts of the mirror, do again return upon us from thence, it is not possible that all reflections should be made at equal angles. Though those who closely impugn our opinion contend that, by these reflections of light from the moon upon the earth, the equality of angles is taken away, thinking this to be much more probable than the other.

Nevertheless, if we must of necessity yield and grant

But in brief, said he, I wonder how they come thus to allege against us the half-moon, there being the same reason when she is gibbous and crescent. For if the sun enlightened the moon, as a mass of ethereal or fiery matter, he would never surely leave one hemisphere, or half of her globe always appearing dark and shadowy to sense, as it is seen to be; but how little soever he touched her superficies, it would be agreeable to reason that it should be wholly replenished and totally changed by that light of his, which by reason of its agility and swiftness so easily spreads and passes through all. For, since wine touching water only in one point, or one drop of blood falling into any liquor, dyes and colors it all with a red or purple color; and since they say, that the very air is altered and changed with light, not by any defluxions or beams intermingled,

But forasmuch as she is not only enlightened herself, but also sends back hither the image of her illumination, this confirms us yet further in what we say touching her substance. For reflections and reverberations are not made upon any thing which is rare, and of thin and subtile parts; nor is it easily to be imagined how light can rebound from light, or one fire from another. But that which is to make the reverberation or reflection must be solid and firm, that a blow may be given against it and a rebounding made from it. As a proof of this, we see that the air transmits the sun, and gives him a way to pierce quite through it, not obstructing or driving back his rays; but on the contrary from wood, stones, or clothes put in the sun, there are made many reflections of light and many illuminations round about. So we see that the earth is illuminated by him, not to the very bottom, as the water, nor thoroughly and all over, as the air, through which the beams of the sun have a clear passage; but just such a circle as surrounds the

But what arguments, said he, were alleged after this?

The moon, answered I then, suffered the same eclipse.

You have done well, replied he, to put me in mind of it. But would you have me go on and prosecute the rest of the discourse, as if you had already supposed and granted that the moon is eclipsed, being intercepted within the shadow of the earth? Or shall I take for the subject of a declamation the making a demonstration of it, by rehearsing to you all the arguments, one after another?

Nay, by Jove, said Theon, let this be the argument of your discourse. For I indeed stand in need of some persuasion,

Then said Lucius: These are the principal points, and the summary of what is said. But in the first place, if you please, take the argument drawn from the form and figure of the shadow. For this is a cone, as it must be when a great fire or light that is spherical encompasses a mass that is also globular but less; whence it comes that, in the eclipses of the moon, the circumscriptions of the black and dark from the clear and luminous have their sections always round. For the sections given or received by one round body applied to another, which way soever they go, do by reason of the similitude always keep a circular form. Now as for the second argument, I suppose you understand that the first part which is eclipsed in the moon is always that which looks towards the east, and in the sun that which regards the west. Now the shadow of the earth moves from the east to the west, but the sun and moon from the west eastward. The experience of the appearances gives us a visible knowledge of this, nor is there need of many words to make us fully understand it; and from these suppositions the cause of the eclipse is confirmed. For, inasmuch as the sun is eclipsed by being overtaken, and the moon by meeting that which makes the eclipse, it probably or rather necessarily follows that the one is surprised behind, and the other before. For the obstruction begins on that side whence that which causes it first approaches. Now the moon comes upon the sun from the west, as striving in course with

The third argument is taken from the time and greatness of the eclipses. For the moon, if she is eclipsed when she is on high in her apogee (or at her farthest distance from the earth), continues but a little while in her defect or want of light; but when she suffers the same accident being low and in her perigee (or near the earth), she is very much oppressed, and slowly gets out of the shadow; and yet, when she is low, she moves swifter, and when high, slower. But the cause of the difference is in the shadow, which is, like pyramids, broadest at the bottom or basis; and, growing still narrower by little and little, terminates in a sharp point at the top. Whence it comes, that when she is low, she is embarrassed within greater circles, traversing the bottom of the shadow and what is most obscure and dark; but when she is high, being through the narrowness of the shadow (as it were) but in a shallow puddle, by which she is sullied, she immediately gets out again. I omit what was said particularly about the bases and disposition of parts, for these admit of a rational explanation, so far as this is possible; but I return to the subject properly before us, which has its foundation in our senses. For we see that fire shines forth and appears brighter out of a dark and shady place, through the thickness of the caliginous air, which admits no effluxions or diffusions of the fire’s virtue, but keeps in and contains its substance within itself. Or rather,—if this is a passion of the senses,—as hot things, when near to cold ones, are felt to be hotter, and pleasures immediately after pains are found more vehement, so things that are bright appear better when they are near to such as are obscure, the imagination being more strained and extended by means of different passions. But there seems to be a greater appearance of probability in the first reason.

If it were then true that the moon, being, as the Stoics say, a muddy and troubled star, has a weak and duskish fire, it would be meet that she should suffer none of these accidents which she is now seen to suffer, but altogether the contrary; to wit, that she should be seen when she is hidden, and absconded when she appears; that is, she should be concealed all the rest of the time, being obscured by the environing air, and again shine forth and become apparent and manifest for six months together, and afterwards disappear again five months, entering into the shadow of the earth. For of four hundred and sixty-five revolutions of ecliptic full moons, four hundred and four are of six months’ duration, and the rest of five. The moon then should all this time appear shining in the shadow; but on the contrary we see, that in the shadow she is eclipsed and loses her light, and recovers it again after she is escaped and got forth of the shadow. Nay, she appears often in the daytime, so that she is rather any thing else than a fiery and starry body.