Moth above stacked geometric solids

The moth came in on the third night of the rain, drawn to the lamp in the scriptorium while I was copying the proof for the fifth solid. Brother Anselm says moths only want the warmth, but I think he is wrong, because this one settled on the parchment exactly over my dodecahedron and did not stir until the bell for matins. Its wings were the colour of old vellum with dark patches like the lichen on the north wall, and when I looked closer the patches were made of tiny dots, thousands of them, as if someone had pricked the wings with a needle dipped in ink.

Prior Wenceslas found me with my candle nearly out and the moth still there. He asked what I was doing, and I told him the truth: that I had been trying to prove there are only five regular solids and that the world must be built from them. He looked at the moth for a long time, then at my sheet, and said God is not obliged to use the figures we find most pleasing. He lifted the lamp so the light fell across the wings, and I saw faint shadows there, a triangle, a cube, the bones of an icosahedron, as though the moth had been carrying the diagram all along.

Then it lifted and went out through the gap under the shutter into the wet dark. I have copied the formula into the margin where it sat, a over b, the proportion Brother Anselm says the Greeks held to be most pleasing. I do not know if it is right. I only know that the next morning the sheet was free of dust, and the ink had not smudged where its feet had been.

Write to me before the feast. Tell Mother I am eating.