Leonardo conceives of form as an entity that can be endlessly transformed, according to rules of geometry and proportion that have, to his mind, characteristics of absolute regularity and harmony. He attempts to show the presence of these laws in all spheres of nature: from the human body to those of animals, from the branches of trees to those of rivers, from geometric shapes to those of fossils. This concept of the infinite malleability of forms is a salient feature of his entire activity as artist, designer of machines and investigator of the phenomena of the physical world.