Because none of Leonardo's sculptural projects was brought to completion, his approach to three-dimensional art can only be judged from his drawings. The same strictures apply to his architecture: None of his building projects was actually carried out as he devised them. In his architectural drawings, however, he demonstrates mastery in the use of massive forms, a clarity of expression, and especially a deep understanding of ancient Roman sources.

As a scientist Leonardo towered above all his contemporaries. His scientific theories, like his artistic innovations, were based on careful observation and precise documentation. He understood, better than anyone of his century or the next, the importance of precise scientific observation. Unfortunately, just as he frequently failed to bring to conclusion artistic projects, he never completed his planned treatises on a variety of scientific subjects. His theories are contained in numerous notebooks, most of which were written in mirror script. Because they were not easily decipherable, Leonardo's findings were not disseminated in his own lifetime; had they been published, they would have revolutionized the science of the 16th century. Leonardo actually anticipated many discoveries of modern times. In anatomy he studied the circulation of the *lo** and the action of the eye. He made discoveries in meteorology and geology, learned the effect of the moon on the tides, foreshadowed modern conceptions of continent formation, and surmised the nature of fossil shells. He was among the originators of the science of hydraulics and probably devised the hydrometer; his scheme for the canalization of rivers still has practical value. He invented a large number of ingenious machines, many potentially useful, among them an underwater diving suit. His flying devices, although not practicable, embodied sound principles of aerodynamics.