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Paris Manuscript F — 176

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Bibliothèque de l'Institut de France, Paris

Delle macule della luna.

Essi detto che le macule della luna son create in essa luna da essere in sé di varia raretà e densità; il che se così fussi, nell'eclissi della luna i razzi solari peneterrebbono1 per alcuna parte della predetta raretà; il che non si vedendo tale effetto, tale oppenione è falsa.

Altri dicano che la superfizie della luna essendo tersa e pulita, che essa a similitudine di specchio riceve in sé la similitudine della terra. Questa openione è falsa, con ciò sia che la terra scoperta dall'acqua per diversi aspetti2 ha diverse figure. Adunque quando la luna è all'oriente, essa specchierebbe altre macchie che quando essa ci è di sopra, o quando essa è in occidente; il che3 le macchie della luna, come si vede nel plenilunio, che mai si variano nel moto da lei fatto nel nostro emisperio. Seconda ragione è che la cosa specchi[a]ta nella convessità piglia piccola parte d'esso specchio, com'è provato in prospettiva. Terza ragione è che nel plenilunio la luna vede solo il mezzo della spera della terra alluminata, nella quale l'Ocean colle altre acque r[i]splendano, e la terra fa macule in esso splendore, e così si vedrebbe la metà della nostra terra cinta dallo splendore del mare alluminato dal sole, e nella luna tal similitudine sarebbe minima parte d'essa luna. Quarta è che la cosa splendida non si specchia nell'altra splendida. Adunque il mare pigliando splendore dal sole, sì come fa la luna, e' non si potrebbe in lei specchiare tal terra, che ancora specchiar non vi si vedessi particularmente il corpo del sole e di ciascuna stella a lei opposita.

Nel margine destro due piccole figure di sfere, la seconda con:

r a - q4

On the spots of the moon

It has been said that the spots of the moon are created in the moon itself by its having in itself various rarity and density; which, if it were so, in the eclipse of the moon the solar rays would penetrate through some part of the said rarity; and since this effect is not seen, such an opinion is false. Others say that the surface of the moon, being smooth and polished, receives in itself, in the manner of a mirror, the likeness of the earth. This opinion is false, since the earth uncovered by water has different figures from different aspects. Therefore when the moon is in the east it would mirror spots different from those it mirrors when it is above us, or when it is in the west; whereas the spots of the moon, as is seen at the full moon, never vary in the motion it makes through our hemisphere. The second reason is that a thing mirrored in a convex surface occupies a small part of that mirror, as is proved in perspective. The third reason is that at the full moon the moon sees only the middle of the sphere of the illuminated earth, in which the ocean with the other waters shines, and the earth makes spots within that splendour; and so one would see half of our earth girded by the splendour of the sea lit by the sun, and in the moon such a likeness would be a very small part of that moon. The fourth is that one shining thing is not mirrored in another shining thing; therefore the sea, taking splendour from the sun as the moon does, could not have such earth mirrored in it without there also being seen mirrored in particular the body of the sun and of every star opposite to it.

In the right margin, two small figures of spheres, the second with:

r a - q

On the Spots of the Moon: Against Rarity and the Mirror Theory

Four reasons the moon cannot be a mirror reflecting the earth and seas

Astronomy Optics & Light

Continuing the lunar-spot argument, Leonardo dismisses two further explanations: that the spots come from varying rarity and density (disproved because solar rays would then pierce the moon during an eclipse), and that the moon's polished surface mirrors the earth. He offers four reasons against the mirror idea, drawing on perspective and reflection: a convex surface captures only a tiny part of what it reflects, the spots never shift as they would if the moon mirrored a turning earth, and one shining body cannot mirror another. Two small spheres are sketched in the right margin, the lower lettered r, a, q.

On this page

Rarity and density disproved by the lunar eclipse

It has been claimed that the moon's spots come from its varying rarity and density. Leonardo answers that if this were so, during an eclipse of the moon the sun's rays would pass through the rarer parts. Because no such effect is seen, the opinion is false.

Four reasons the moon is not a mirror of the earth

Against the view that the polished moon reflects the earth like a mirror, Leonardo gives four reasons: the spots never change as they would if a turning earth were mirrored; a convex mirror captures only a small part of what it reflects, as proved in perspective; at the full moon only the illuminated half of the earth, with its shining seas, could be mirrored as a tiny part of the moon; and one shining body cannot mirror another, or the sun and stars would be seen in it too.

Reader's Edition — described with AI from the e-Leo transcription.