LEONARDO DA VINCI unsuccessfully tests a flying machine. More on Leonardo on the anniversary of his birth, but for now, as an engineer, Leonardo conceived ideas vastly ahead of his own time, conceptualizing a helicopter, a tank, concentrated solar power, a calculator, and the double hull, and outlining a rudimentary theory of plate tectonics. Relatively few of his designs were constructed or even feasible during his lifetime, but some of his smaller inventions such as an automated bobbin winder and a machine for testing the tensile strength of wire entered the world of manufacturing unheralded. As a scientist, he greatly advanced the state of knowledge in the fields of anatomy, civil engineering, optics, and hydrodynamics.

Beyond friendship, Leonardo kept his private life secret. Within his own lifetime his extraordinary powers of invention, his “outstanding physical beauty”, “infinite grace”, “great strength and generosity”, “regal spirit and tremendous breadth of mind” as described by Vasari  attracted the curiosity of others.

Many authors have speculated on various aspects of Leonardo’s personality. His sexuality has often been the subject of study, analysis and speculation. This trend began in the mid 16th century and was revived in the 19th and 20th centuries, most notably by Sigmund Freud.

Leonardo’s most intimate relationships were with his pupils Salai and Melzi, Melzi writing that Leonardo’s feelings for him were both loving and passionate. It has been claimed since the 16th century that these relationships were of an erotic nature. Since that date much has been written about his presumed homosexuality and its role in his art, particularly in the androgyny and eroticism manifested in John the Baptist and Bacchus and more explicitly in a number of drawings.