should not be sufficiently cemented, they may be stopped by the ashes. Aqueducts of tubes have this advantage — if any damage happen, any person may rectify it, and water from earthen tubes is far more wholesome than that from pipes, as the use of lead is found to be pernicious. We should not, therefore, conduct water in pipes of lead, if we would have it wholesome. The taste also of that from the tubes is better, as is proved by our daily meals ; for all persons, although they have tables furnished with silver vases, use fictile ware on account of the purity of the water. We add to this detailed extract from Vitruvius, the directions of Pliny for water conduits, chiefly because of the explicit assertion it contains of the law, that fluids will always rise to the level of their head. " If," says this author, " a man would convey water from any head or spring, the best way is to use pipes of earth made by the art of the potter, they ought to be two finger's thick, and one jointed within another, so that the end of the upper pipe enters into the end of the under one, as a tenon into a mortice, or a box into the lid ; these pipes ought to be laid even with quick lime, quenched and dissolved in oil. The least level to carry and command water up hill from the descent is 100 feet, but if it be conveyed by one canal only, it may be forced to mount 240 feet. As touching the pipes by means whereof the water is to rise aloft, they ought to be of lead ; this is also to be observed, that the water always ascends of itself at the delivery, to the height of the head whence it flowed. If it 12 PRELIMINARY ESSAY. be fetched a long distance, the work must rise and fall often, that the level may be still maintained ; the pipes ought to be 10 feet long ; the pipes were named from the number of finger's breadths of which the sheet of lead was formed before it was turned into the shape of a pipe, and they were also to be of different thicknesses. In every turning and winding of a hill, the pipe should be five finger's round, and no more, to repress and break the violence of the water in the current." From this description of the mode in which the Roman aqueducts were constructed, it is obvious that the principles and precautions, which, as is sometimes supposed modern science has discovered and applied to such structures, were known and used at that early day. The declivity given to the channel was indeed greater than that usual in more mo- dern conduits, but in other respects, few or no improvements or alterations in the manner of building and securing such works, seem to have been made. It will, however, strike the reader with surprise, to find that leaden pipes were used and found equal to resist the pressure of columns of water, even in passing it down and up steep declivities. In subsequent pages, some remarkable instances of this will be present- ed. Iron pipes seem to have been wholly unknown to the Romans. Indeed, the first castings of iron we hear of, were made in England, as is related by Baker, in his Chronicles of the Kings of England, about the year 1545, in the 35th year of Henry VIII., by Ralph Hage and Peter Bawde. 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 introduced, be eligible : " If it be an open and running stream, you are carefully to ob- 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 bot- tom, it may be deemed good. Again, if vegetables boiled in it be rapidly cooked, it