PEOGRESS OF THE ARTS. 251 



cised if it were not so. Hence the writings of architects and engineers 

 during the middle ages do really form a prelude to the works on scien- 

 tific mechanics. Vitruvius, in his Architecture, and Julius Frontinus, 

 who, under Vespasian, wrote On Aqueducts, of which he was super- 

 intendent, have transmitted to us the principal part of what we know 

 respecting the practical mechanics and hydraulics of the Romans. In 

 modern times the series is resumed. The early writers on architecture 

 are also writers on engineering, and often on hydrostatics : for exam- 

 ple, Leonardo da Vinci wrote on the equilibrium of water. And thus 

 we are led up to Stevinus of Bruges, who was engineer to Prince Mau- 

 rice of Nassau, and inspector of the dykes in Holland ; and in whose 

 work, on the processes of his art, is contained the first clear modern 

 statement of the scientific principles of hydrostatics. 



Having thus explained both the obstacles and the prospects which 

 the middle ages offered to the progress of science, I now proceed to 

 the history of the progress, when that progress was once again re- 

 sumed. 



