Galileo's mature views on dynamics received expression in a work published in 1638, _Mathematical Discourses and Demonstrations concerning Two New Sciences relating to Mechanics and Local Movements_. It treats of cohesion and resistance to fracture (strength of materials), and uniform, accelerated, and projectile motion (dynamics). The discussion is in conversation form. The opening sentence shows Galileo's tendency to base theory on the empirical. It might be freely translated thus: "Large scope for intellectual speculation, I should think, would be afforded, gentlemen, by frequent visits to your famous Venetian Dockyard (_arsenale_), especially that part where mechanics are in demand; seeing that there every sort of instrument and machine is put to use by numbers of workmen, among whom, taught both by tradition and their own observation, there must be some very skillful and also able to talk." The view of the shipbuilders, that a large galley before being set afloat is in greater danger of breaking under its own weight than a small galley, is the starting-point of this most important of Galileo's contributions to science. Vesalius (1514-1564) had in his work on the structure of the human body (_De Humani Corporis Fabrica_, 1543) shaken the authority of Galen's anatomy; it remained for Harvey on the basis of the new anatomy to improve upon the Greek physician's experimental physiology. Harvey professed to learn and teach anatomy, not from books, but from dissections, not from the dogmas of the philosophers, but from the fabric of nature. There have come down to us notes of his lectures on anatomy delivered first in 1616. A brief extract will show that even at that date he had already formulated a theory of the circulation of the blood:-- "[Illustration: WH monogram][1] By the structure of the heart it appears that the blood is continually transfused through the lungs to the aorta--as by the two clacks of a water-ram for raising water. "It is shown by ligature that there is continuous motion of the blood from arteries to veins. "Whence Δ it is demonstrated that there is a continuous motion of the blood in a circle, affected by the beat of the heart."