Chap. IV.
HOMAN.
165
10 inches above low water, and the rise is one-sixth of the span ; the arches arc 3 feet2 inches thick. The breadth of the piers is 2G feet 3 inches, and that of the bridge, 33 feet9 inches. Hie facings of the piers are worked stone, with well executed mouldings. Theother parts of the structure are of rubble; the foundations rest on a general framework,surrounded and crossed by several rows of piles. A defect which occurred under one ofthe piers of the bridge was repaired in 1811 by the elder Goury.
Bridge of Verona over the Adige consists of three arches, 36, 50, and 160 feet span ; thelatter is the largest arch found in Italy .
Bridge on the Marachia f near Rimini, has five arches, from 23 feet 3 inches to 28 feet9 inches span. The upper part of the piers has niches and columns, supporting entabla-tures.
Water. — The Romans bestowed unwearied pains to obtain pure and wholesome water ;their military and civil engineers were always on the alert to ascertain its nature and pro-perties throughout the countries where they were employed. Vitruvius observes thatwhen C. Julius, the son of Masinissa , lodged with him, they frequently conversed on sub-jects of natural history, and that he had read most of the Greek authors, as Theophrastus ,Herodotus , &c., with the greatest care and attention, for the purpose of ascertaining thequalities of the different streams and rivers. The vast sums of money expended to provideabundance of pure water for the inhabitants of the imperial city and the other towns ofthat vast empire, gave employment to many engineers ; it is curious to examine the opinionsof Greek and Roman philosophers upon the nature and properties of this element. Thales,the Milesian, taught that all things originated from, and the priests of Egypt believedthat all things were composed of, water; that it was essentially necessary for the purposesof life, for pleasure, and for daily use, was universally felt and admitted.
When the Roman engineer wished to discover the source of a stream, he was instructedto lie down on the ground a little time before sunrise, and to notice where the vapours roseinto the air; he was then to dig at that spot and commence his search. In clay it wassupposed the supply was small, and not of the best quality ; but in veins of gravel that itwas well flavoured; when the bulrush, the wild willow, the alder, reeds, ivy, and similarplants abounded, abundance was always relied on. In situations where these indicationswere not met with, they adopted the following plan: a hole three feet square was dug,at least five feet deep, and in it, about sunset, a brass or leaden vessel was placed, rubbedinside with oil. Thus prepared it was inserted, and the upper part of the excavationcovered with reeds or leaves, over which the earth was thrown. If on the followingday, on opening the hole, the inside of the vessel exhibited any drops of water, it was ex-pected that a quantity might be obtained. When the vessel placed in the pit was made ofunburnt clay, it was often found destroyed by the moisture, which was considered a sureindication of the presence of water. A fleece of wool was often placed in a similar pit,and when water on the following day could be pressed out of it, an abundant supplywas inferred. Lamps full of oil were placed in the pit and covered over, and whenexamined, if not exhausted, but still retaining some of the wick and oil, and presenting ahumid appearance, it was shown that water might l>e found, as it was supposed that heatinvariably drew moisture towards it. Such were the rude trials recommended previous tothe sinking of a well, which were continued until the head of the spring was found ; otherwells were then dug around it, and by means of tunnelling connected with it.
Rain water was considered by Celsus the physician the most pure, and formed of thelightest vapours. Aristotle supposed that these vapours rose from the earth, into a coldregion of the air, were then compressed into clouds, and afterwards condensed into rain;that such water collected into showers was cleansed by its passage through the air. AndVitruvius tells us further, that showers do not so frequently fall upon plains as upon highground, because the vapours are driven to the mountains. The winds convey the waterwhen heated by the sun, from the low grounds to the higher, and thus keep up a constantcirculation ; and he further illustrates this by his observation of the drops of water whichcollect on the ceiling of a hot bath ; hot vapours ascend at first from their lightness, and donot fall down, but when condensed, they drop on the heads of the bathers; so it is withair warmed by the sun, it raises moisture from all places, and gathers it into clouds, whilstthe winds which blow from cold quarters bring dry air and not vapours.
Some hot springs produced excellent flavoured water, and many cold ones had bothbad taste and smell; the Romans arranged these, made them serviceable to a variety ofpurposes, and had baths supplied with water adapted, as they supposed, to every speciesof malady. Some springs, where the water was acid, as those found at Lyncestis in Italy ,the Yelinus, and in the Campana near Theanum, had the property of dissolving the stonewhich forms in the bladder; eggs placed in such water had their shells softened anddissolved; lead became white by the application of an acid, and brass verdigris. Pearlsand flint stones, upon which fire would have no effect, were speedily dissolved in the sameway by the application of acids. Such were the qualities and properties they found in someof the waters, and the Romans seem on all occasions to have exercised their knowledge,
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