188

HISTORY OF ENGINEERING.

Book I.

di Bianio, the Naviglio Ferranesc. The Gulf of Venice is connected with the Po by acanal, 6 miles in length, called Val d’ Albama.

Besides these are a vast number of branches, which are solely used for the purposes ofirrigation.

Ferrara is connected with Venice by the Po and several canals; the canal Ponfilio con-ducts to Pont di Lago Oscuro ; here the Po is entered, and its navigation continues forforty miles; when passing four miles along the canal of Cavenelta, the village of Eaurio isarrived at. At nine miles upon the Adige are the sluices of Brondo, which are only 28miles from Venice ; soon after the Venetian lagunes are entered. The Bachiglione wasformerly the chief navigation at Padua ; at Vicenza it unites with the Rherone, and thenit becomes navigable for vessels of considerable burthen. After passing Padua for fifty miles,its course is winding, and it then enters the Levant at Bundolo. Between Padua andVicenza are several sluices. These sluice gates, or pertuis, as they have been designated,were thus contrived.

The lower beam of each gate was framed with the head and heel posts, so as to allow aspace of 6 inches between it and the sill. From the middle beam to the top, the gateswere planked over in the ordinary way ; the lower part was left open, or in skeletonframing, and was closed by paddles or sluices, w’hich w*ere moved up and down by a rackand pinion. When the paddles were let down, they descended three or four inches lowerthan the surface of the floor on the low'er side, which acted as a rebate, against whichthey pressed, and effectually shut the lock. They also had a bearing against the lower cross-beam of the gate, and the head and heel posts rested on square stones, made fast in the sill.

To make use of gates upon this construction, it was necessary first to raise the paddle ashigh as the lower cross-beam, which permitted the water to pass through at the foot of thegate. The paddles were then elevated to the height of the middle beam, which was placedat the ordinary level of the water, usually 4 or 5 feet deep upon the sill.

These gates were easily opened, as the boarded part was entirely out of the water, and adeposit on the floor of the chamber of the lock could form but little obstruction, as fromthe scour of the water, the greater part would be washed away. The only serious objectionto this early contrivance in aid of internal navigation is the injury that vessels mightsustain at the time they were passing through, when one half of their length would be outof the water, producing a considerable strain upon them. The water passing through aspace, walled in on both sides, would, to a certain extent, allow the barge or vessel toslide down an apparent plane ; but, before it could again resume its level position, it wouldbe subjected to another strain. These side walls were, however, made of considerablelength, a foot being usually allowed for every inch of fall; a timber floor was laid through-out, to prevent the force of the water from deepening and undermining the foundations.

Bassanallo had a canal 1 ] miles in length, at the commencement of the thirteenth century ;in its passage it passed two aqueducts, and the vessels loaded with stone to Venice chieflynavigated it.

The Brenta is navigable fifteen miles above Padua , and it unites with the Bachiglione afew miles beyond that city. There is also a communication with the Adige by a canal sixmiles in length. Another cut, 20 miles in length, passes from Padua to Venice ; its fall of50 feet is divided into four locks.

In the lagunes are several canals ; one which skirts them, called the Novella Brenta, is86 miles in length.

At Leghorn is a fine canal 15 miles in length, 45 feet in breadth, and 4 feet in depth,w’hich receives its supply from the Arno. Men usually haul the vessels, the fall beingscarcely perceptible.

Drainage. — The Pontine marshes derive their name from an ancient town called Po-metia, whose exact site is not known, and which had totally disappeared before the time ofPliny. They comprise that part of the Campania or ancient Latiuin situated on the south-east of Rome, and on the confines of Naples . Their length is about 42,000 metres, ex-tending from Cisterna to Terracina ; their width is not so much : their longitudinal axisis from south-east to north-w’est, the direction of the celebrated Appian Way , w’hich, incrossing their marshes, is almost parallel to the shores of the Tyrrhenian Sea .

At the south-eastern extremity is the ancient Auxur or Terracina, the distance of whichplace from the house now* called Bonificazione, to the port S. Sebastian, or Porta Capennaat Rome, where the Appian Way formerly issued, is 91,841 metres, about 62£ ancientmiles, each of which is equal to 1471 *2 metres.

The distance from the above points to the Porta S. Giovanni, which is the route nowfollowed, is 101,120 metres : this modern route pursues the Appian Way for 45,000 metres,which is comprised betw*een Terracina and Cisterna . The shortest distance between thehouse of Bonificazione and the gatesof S. Sebastian and S. Giovanni, are 90,421 metres, andto the latter 91,025 metres.

Starting from Terracina, and following the edge of the marsh, we find it separatedfrom the sea by a narrow down : a similar tract of land, much more considerable, and an