Labels:text | screenshot | font OCR: In the text at the upper left, Leonardo cites a lost work by Leon Battista Alberti on ships, and On Aqueducts, by the Roman writer Frontinus. A He continues to work with the accepted ideas and writings of the time, but explores their conclusions in his own ways. On this page Leonardo gives a description of a seagoing clock and tells of ways to measure the course and speed of a ship. At first glance, these concepts seem out of place in the codex, but actually they are the keys to understanding that sheet 13 is intended as a practical guide for