kinds of platted vessels are woven; some of these vessels are capable of holding water, when covered over with asphaltus; others are used with the material in its natural state. Sails are also made of reeds; these resemble mats or hurdles. 10. It is not, perhaps, possible to prevent inundations of this kind altogether, but it is the duty of good princes to afford all possible assistance. The assistance required is to prevent excessive overflow by the construction of dams, and to obviate the filling of rivers, produced by the accumulation of mud, by cleansing the canals, and removing stoppages at their mouths. The cleansing of the canals is easily performed, but the construction of dams requires the labour of numerous workmen. For the earth being soft and yielding, does not support the superincumbent mass, which sinks, and is itself carried away, and thus a difficulty arises in making dams at the mouth. Expedition is necessary in closing the canals to prevent all the water flowing out. When the canals dry up in the summer time, they cause the river to dry up also; and if the river is low (before the canals are closed), it cannot supply the canals in time with water, of which the country, burnt up and scorched, requires a very large quantity; [CAS. 740] for there is no difference, whether the crops are flooded by an excess or perish by drought and a failure of water. The navigation up the rivers (a source of many advantages) is continually obstructed by both the above-mentioned causes, and it is not possible to remedy this unless the mouths of the canals were quickly opened and quickly closed, and the canals were made to contain and preserve a mean between excess and deficiency of water.