The actual bcd of the Po, which carries the waters of this great river to the sea, which is named Po de Ve nice, was formed in 1167 by an opening in the dykes at Tevaralo. Besides the Cavanello di Adige, there is another sluice at Brondolo, which has 12 feet fall.
The lagunes are skirted by a canal 36 miles in length, named Novella Brenta. The Sill river commences in the plain, some miles above Treviso, and is navigable from that city to the sea, a distance of 40 miles by the river. It still communicates with the lagunes by a ca nal named Siomello, which has two sluices ; and the gates, constructed in 1686, have eight feet fall.
At Rome it has often been proposed to make the Ti ber navigable from Perugia to the mouth ol the Nera, from whence to the sea it is now navigable. But INlan fredi, in a report dated 1732, says, that the Tiber, hav ing a fall of eight or nine Roman palms per mile, is too rapid for navigating upwards : he therefore proposes sluices ; but the project was abandoned.
The canal of Leghorn is the most considerable in Tuscany. It is 15 miles long, 45 feet broad, and four or five feet deep. It derives its waters from the Arno, and falls towards Leghorn ; but the slope is so gentle that barks easily pass upwards, hauled by men. The river Arno continues navigable through Floienee to Ar raro, where the Canal di Chiano prolongs the naviga tion to Alonto Pulciano.
Holland and the LOW Countries The northern part of Germany is one immense plain, descending gently towards the sca, there being no con siderable mountain within 150 miles of it ; and from Blankness, at the Dover Straits, to the coast of Den mark, the shore exhibits chiefiv a range of low sand hills, occasionally broken to admit the exit of the land waters from the great plain.
Behind this range of sand hills lies a shallow basin, about a mile in width, occupied by a bog or morass, the surface of which is but little above the level of the sca, and the bottom from ten to twenty feet below it. The breadth of this space frequently varies, the great inlets of the Zuyder-Zee still exist, unfilled with peat ; and, according to tradition, was a lake only, until the Cim brian deluge, breaking the northern boundary of the mo rass, had admitted the sea into Ft iesland. But the con tinuous parts of the morass are chiefly adjacent to great rivers. Now, it is the nature of all rivers liable to in undation, to deposit great part of the sullage on their immediate banks, and raise them higher than the mo rass behind ; and this valuable land may have suggested the idea of completing and extending the works, by em banking the rivers, and securing the nn.taclows by. dykes. The embankments of the Rhine, at least of the great island Betuwe, is more ancient than the invasion ol Cxsar. Although the state of the country must have rendered inland navigation unavoidable, yet it does not appear that any artificial canal was constructed previous to the time of the Romans, when Drusus formed the derivation frotn the Rhine to the Yssel at Dxsburg, 12 B. C. (Tacitus, Jinn. ii.) Ile is also said to havt: em
banked the Rhine. Corbulus, one of the ablest of the Roman Generals, employed his soldiers in excavating the Fossa Corbulonis, to unite the Rhine and the Meuse. It was twenty-three miles in length ; and may have been the origin of the present canal of Delft, extending from Leyden to Maesland sluice. Claudius Civilis formed the river now called the Leek. This river pass es with a crooked course, and on a high level, to join the Aleuse at Flaardirgen. It has been embanked in later times.
In the middle of the fifth century, the channel of the Merwe, or Merwede, was formed by Aleroveus, king of the Franks, from the Meuse to the Waal, at Dordtrecht, to join the Leck at Krimpen; the mouth of which is now considered as the mouth of the Meuse.
The Emperor Otho, in the tenth century, cut a ca nal from Gheet to the sea ; and besides the beforenten tioned, many cuts and channels have been effected by inundations. Of this kind are the Risbosch, (or Bul rush Forest,) to the westward of the city of Dordtrecht, which occurred in 1421, by 311 irruption of the Aleuse.
Besides the natural lakes, the interior navigations are continually extending, by cutting turf for fuel, which, reaching to the depth of from twelve to twenty fcet be low low water, leaves a new lake. These sheets of water, called Nasser], or Plashes, by the Dutch, are all one level within ceitain districts, and uniting with the canals, are navigated by the sail or perch; but as many of these plashes, when united, form great lakes, which have waves, and which cot-rode the adjacent lands, it is the policy of the Dutch to have them drained and cultivated. For this purpose they are surrounded by dykes, to keep out the foreign waters; on the outside of which a ringsloot, or surrounding drain, is made of dimensions sufficient to be a navigable canal. The wa ter is then raised from the interior polder by means of windmill, to the ringsloot, along which it passes into the sea. The bottom of the polder, or drained land, has also drains, which in some cases are navigable, but they never communicate with the exterior canal, or rings loot. Neatly all [lie lakes of North Holland were re claimed in this way about 150 years ago : Aluch has also been done in South Holland. To the extent of about 20,000 acres, has been lately drained under the direction of the intelligent M. Brunings of Leyden. Great part of that province is however still under water, especially adjacent to Rotterdam.