Pipes of cast iron are now the only ones used for mains, or large distributing pipes. These may be made of almost any diameter, by duly increasing the quantity of metal contained in them. The largest pipes laid down in this city, are of three feet internal diameter, and in lengths of nine feet, weighing from 3,500 to 3,800 Ibs. The largest diameter of leaden pipes used by the Romans, was of 12 inches internal bore.

Vitruvius lays down these rules for determining whether the waters that are to be " If it be an open and running stream, you are carefully to obintroduced, be eligible :

serve the manners of men and their conformation, that live around its source and if they be of robust frame, bright complexion, without deformed limbs, or blear eyes, the stream may be surely approved. Or, if the water thrown into a vessel of Corinthian brass shall leave no spot, it may be pronounced excellent. Or, boiled in a like vessel, and left to cool, if, when poured off, there shall be neither sand nor earth left at the bottom, it may be deemed good. Again, if vegetables boiled in it be rapidly cooked, it is an indication that the water is pure and wholesome."* For 441 years after the building of their city, the Romans were content to use the water furnished by the Tiber, (the yellow Tiber,t as Horace calls it) by wells, or fountains. * t Ode 2 r lib. E. Vitruvius, chap, v., lib. viii.