Leonardo di Ser Piero da Vinci was born near Florence in 1452 and died near Amboise, France, in 1519. In 1939, 420 years after his death, a great exhibition of the master’s works was held at Milan and parts of it were shown in the next year at the Museum of Science and Industry in Rockefeller Center, New York. The Milan exhibit included works in the following fields: studies and drawings in mathematics, astronomy, geology, geodesy, cosmography, map-making, hydraulics, botany, anatomy, optics (including proof of Alhazen’s problem of measuring the angle of reflection of light), acoustics, mechanics, and flying; not to mention sculpture, painting, drawing, sketches, architecture, town planning and military arts and sciences. Da Vinci is best known today for his paintings, such as the renowned “Last Supper”, beloved everywhere, and the “Mona Lisa”. He was one of the truly universal geniuses. There was little indeed that he could not do. Leonardo’s study of optics and perspective was reported in his _Treatise on Painting_, written about 1515 and first published at Paris in 1651, but well known prior to that time through manuscript copies. Da Vinci has been a great trial to the students and historians, for he wrote in his own special form of shorthand which was found to be extremely hard to decipher. Da Vinci experimented with the _camera obscura_ and wrote an accurate scientific description of it, preparing the way for the men who were to make the machine a practical medium. Vasari in his famous _Life of Leonardo_ points out that he gave his attention to mirrors and learned how they operated and how images were formed. But more important than this, he studied the human eye and was the first to explain it accurately, using the camera as his model, and in this way he really learned the fundamentals of its functional principles. To this day the camera is explained in simplest terms as a mechanical eye and the human eye is explained as a marvelous, natural camera. Da Vinci also noted the effects of visible impressions on the eye. Roger Bacon was undoubtedly Leonardo’s master in optics and this is a definite link in the chain of the growing knowledge of light and shadow and of devices which would create illusions for instruction and entertainment. It has been pointed out that Leonardo and Roger Bacon had much in common--both being so far ahead of their own times that they were not understood until centuries later. And both men believed passionately in scientific research and investigation. As an example, Leonardo would spend hours, days or even weeks studying a muscle of an animal appearing in the background of a painting so that it could be drawn perfectly. As a concrete link with Bacon, Leonardo described a mirror camera device which made it possible for people on the inside to see the passerby in the street outside. Bacon, you may recall, achieved and described a similar effect.