1 
Italian Irrigation. 197 
ch.irjre from the new form of outlet in summer and in v/inter. 
7tli. To establish, in the event of a deficiency of supply in the 
main canal, a fair method of decreasing proportionally the dis- 
charges of the different outlets. 8th. To provide for the possible 
contingency of a permanent increase in the supply of the main 
canal, so as to prevent in such case the consumers from getting 
more than their fair share of the Avater. 9th. To make the dis- 
charge of the outlets independent of variations in the level of the 
bottom or bed of the main canal. 10th. To establish, by some 
unalterable mark, the true level of the bed of the main canal at 
each outlet, so that it might be at all times recognisable Avith 
facility, and verified whenever necessary, 11th. To devise such 
a system of management of the outlets as to place in the hands of 
the Government officers the power of either closing them alto- 
gether, or diminishing their discharge with facility in all periods 
of extreme dryness. 12th. To point out in detail the best means 
of reconcilins: the often conflicting: interests of navigation and 
o o o 
irrigation, so that, in periods of extreme dryness, the quantitv of 
water essential for the former might be maintained with the least 
possible inconvenience to the latter." 
Of this problem the three fundamental conditions are : — 
1. To indicate the best unit for the measurement of water 
employed in irrigation, and such a method of distributing it as 
shall be injurious neither to the public treasurj-, to navigation, 
nor to the consumers. 
2. To discover an apparatus wliich shall discharge in a given 
time, by an outlet of fixed dimensions, a constant volume of 
water, whatever may be the variations in the level of the sup- 
plying canal. 
3. To construct the apparatus so that it should oppose all 
possible obstacles to fraud. 
The unit of measure, oncia magistrale, fixed on by Soldati, is 
that quantity of water which flows freely, or under the sole 
influence of pressure, through a rectangular opening, having a 
uniform height of 7"4 local inches (7-86 English inches), a breadth, 
of 3 (4-12 English), and a constant pressure of 2 local inches 
(3*93 English) above the upper edge of the outlet. 
For larger discharges the breadth was doubled, trebled, &c., 
a practice which leads to irregularities favourable to the larger 
openings. The outlets are cut in a single slab of stone, and fitted 
with an iron rim. 
The apparatus required was found in Soldati's Modulo 
Milanese, which, with some modifications, is in use at the pre- 
sent day. 
To explain its present arrangements, Colonel Baird Smith 
published a plan and sections, copies of which are given below. 
