180 
Italian Irrigation. 
the Avhole line of tlie canal. Vigorous efforts were made by tlie 
magistracy to repair the disaster ; and as the State had not the 
necessary funds — 300,000 lire, equal to 40,000/. — extraordinary 
measures were taken to raise money ; the navigation dues were 
raised ; the outlets taxed ; and all parties benefitirig by other 
canals for irrigation were required to contribute. 
In 1751 the Ticino having become the frontier line be- 
tween Sardinia and Lombardy, the supply of water from it 
was guaranteed by treaty, and a priority of right to such 
quantity as might be necessary for this canal was secured to 
Lombardy. 
The length of the Naviglio Grande, from its head at Torna- 
vento to the new dock under the walls of Milan, is 31 miles. 
It runs many miles in a tortuous and deep channel before it 
enters the plain, and there finishes its course, running here in 
cuttings, and there on an embankment. The channel is irregular 
both in breadth and depth ; the slopes are capriciously distri- 
buted, ranging in the upper section from 3'75 to 7-75 feet per 
mile ; the mean slope is 2*84 feet per mile, "very nearly double 
what it ought to be in a well-constructed canal." 
The most important work on this, as on most Italian canals, is 
the great dam which is carried obliquely across nearly the entire 
bed of the Ticino, leaving on the right bank only an opening of 
215 feet in width. This dam has a total length of 918'47 feet; 
its breadth varies from 31 "10 to 58"33 feet, except at one ex- 
tremity where the breadth is only 7"84 feet. 
The means of discharge are supplied by six grand weirs and by 
'twelve escapes comprising 185 sluices, each from 2§ to 2| feet 
in breadth, which are so managed by an upright iron rachet and 
a simple lever, that one man can generally regulate them. 
The ordinary repairs are executed under contract, extending 
over nine years. They amount to about 1700/. per annum, or 
■nearly 55/. per mile. , 
The periodical closing of the canal is commonly effected by 
means of a temporary dam of fascines, piles, &c., erected at a 
point some little distance below the head dam, where the breadth 
of the channel is limited : but from time to time it is necessary 
to raise a dam at the head of tlie canal — an expensive and 
troublesome work. 
Colonel Baird Smith naturally suggests that certain measures 
which would dispense with the construction of any temporary 
dam, would be economical on tlie whole, though they would 
involve a larger outlay in the first instance. 
The discharge from the canal is about 1851 cubic feet per 
second : of this, 369 feet are furnished to branch canals, leaving 
