Perspective of the i
"INTRODUCTION TO PERSPECTIVE:—THAT IS OF THE FUNCTION OF THE EYE.
Behold here O reader! a thing concerning which we cannot trust our forefathers, the ancients, who tried to define what the Soul and Life are—which are beyond proof, whereas those things, which can at any time be clearly known and proved by experience, remained for many ages unknown or falsely understood. The eye, whose function we so certainly know by experience, has, down to my own time, been defined by an infinite number of authors as one thing; but I find, by experience, that it is quite another."
This is an Intro to yet another not-published book by Leonardo da Vinci about perspective and how the eye works. His studies and research on painting and perspective led him to try to understand how the human eye actually functioned. 500 years ago no one really understood how vision actually worked and other authors before him tried to explain it with very limited information - most of which was based off of previous writers.
What Leo used was a precursor to the scientific method. He started his studies from scratch and from their source - the Eye itself. He didn’t just study how vision worked from experience - how his eyes worked - he also dissected human eye balls - going so far as to boiling them with egg whites so they could be cut down the middle and still keep their form.
He realized that what he had read about human vision and the eye was not even close to how our eyes really function. His experiments and implementation of optics are evident in this quote, his art, and the hundreds of thousands of pages of notebooks he left behind.