From 1475 Leonardo da Vinci recorded everyday all his ideas about the nature of the world in its whole variety, in the form of notes in ancient Italian language illustrated with sketches. In this polygraphic bulimia, he accumulated about 13,000 pages, on double-sided sheets folded in half.
Leonardo is neither a scientist nor an engineer in the modern meaning of these terms. He does not waste his time analyzing the consequences of his theories or conceiving the realization of his inventions. In his swarming of ideas, he could be wonderfully right and naively wrong, and he was certainly unable to distinguish between these two extremes.
For this left-hander, the mirror writing is the way he has found so that his thinking is not slowed down by his hand. The use of numerous abbreviations, which makes these texts extremely difficult to decipher, is consistent with this hypothesis. We will never know how he desired exploiting such a unique mass of informations.
These writings were later assembled into notebooks, identified under the more technical term of codex. The Codex Leicester is the only one remaining in private hands. It was sold twice by Christie's, for $ 5.1M on December 12, 1980 and for $ 31M including premium on November 11, 1994. Between these two sales it was named the Codex Hammer. It was bought by Bill Gates at the last auction. The image is shared by Wikimedia.
The Codex Leicester is made up of 18 double sheets of parchment for a total of 72 pages 22 x 30 cm. It brings together his notes written around 1510 on the theme of the water movements. The author imagines that his ideas could be used for the design of bridges.
His observation on the presence of fossils in the mountains brings an explanation far ahead of his time : they were originally in a seabed which was raised by a geophysical phenomenon. This hypothesis is all the more remarkable since the monotheistic religions of his time do not question the creationism.
In the same notebook, he explains the luminosity of the Moon by the reflection of sunlight on its surface entirely covered with water.