From hidden figures to musings on how birds fly, Leonardo da Vinci’s notebooks have long been known as treasure troves of art and science. And it turns out that, 500 years after the master doodled in them, the notebooks still have some secrets. Now, a study of da Vinci’s notes and sketches has revealed something unexpected indeed: the first written evidence of the laws of friction.

In a new study in the journal Wear, an engineer from the University of Cambridge describes how he found the artist’s first writing on the laws of friction in a tiny notebook that dates from 1493 housed in the Victoria & Albert Museum in London. The text and accompanying sketches are apparently evidence of da Vinci’s earliest experiments in friction.

In a statement, researcher Ian Hutchings says that the writing demonstrates that as early as 1493, da Vinci understood the laws of friction. The artist and polymath is now known as the father of tribology, which explores the science of surfaces in motion and how they interact with one another. Friction, lubrication and wear are all part of tribology, and all three topics were explored in depth by da Vinci. He used pieces of dry wood to understand how resistance and friction worked—experiments that have been recreated by other scientists nearly 500 years later.

Hutchings created an extensive timeline of da Vinci’s statements on friction and describes the newly-discovered notes and sketches, which portray blocks being pulled over surfaces with a string. “Friction is of double the effort for double the weight,” wrote the master. This is a different version of Amontons' first law of friction, which states: friction is proportional to the force with which an object is loaded. Guillaume Amontons, after whom the law is named, conducted friction experiments in the 17th century, but the law has long been nicknamed “da Vinci’s law of friction” due to other experiments discovered in his notebooks. Now, it appears that he did indeed state the law 200 years before Amontons, who apparently was unaware of da Vinci’s work in the field.

Ironically, the doodle and text had previously been dismissed by art historians, who preferred to focus instead on a sketch of an old woman adjacent to the scribbles. The artists scribbled the quote “cosa bella mortal passa e non dura” (a line from Petrarch that means “mortal beauty passes and does not endure”) beneath the sketch of the woman. But as long as da Vinci’s notebooks keep revealing the depth of the master’s brilliance, interest in their contents—both artistic and scientific—will never die.

(h/t Gizmodo)