The difference between the requirements of art and science is charmingly shown in the work of Leonardo da Vinci. About the beauty of da Vinci's art, there would seem to be no disagreement. His scientific ideas, however, often showed only the artistic type of beauty. In a sketch of his proposed flying machine, da Vinci was more concerned with making adequate provision for the pilot to step to the ground than with the ability of the machine to fly. He was more concerned with the completeness of what could be appreciated than with the possibility of what could not.