The explanation now follows

of the first copper engraving marked with Number

I.

Water leveling must be done by special instruments.

Since we have now sufficiently shown the testing and verification of water, and we teach nothing else in this chapter except how to level or conduct water, so that it may be led to various necessities and utilities, you should first, for a better understanding of this chapter, note that such libration leveling or balancing is nothing other than a measurement that occurs through sighting, by which one compares the place where the springs originate with the place to which the water is to be led. For as Vitruvius a Roman architect and engineer says, such happens through instruments, of which we intend to present several to your eyes hereafter. And you should read the 6th chapter of the 34th book of Pliny Plinius the Elder, likewise the fifth book of Strabo, and the entire work of Julius Frontinus and Petrus Victor, which describes with great precision the great majesty and powerful water structures built at unspeakable costs, especially the water that was led into the city of Rome. For because in ancient times one noticed the excellent utility of such water conduits, no expense, however high it might have been, was spared, so that everyone thought to serve the common good in such ways, and to attain eternal price and fame. But the leveling or libration (as all authors agree) is the first beginning of all water conduction, whether for gushing fountains or for the drive of incessant motion of various mills and similar artificial water structures, which are driven by the fall, rising, or flowing forward of the water.