200 ' Italian Irrigation. 
flooring of tHe open cliamber has a drop or fall of 1'96 inches at 
H, and an equal quantity distributed uniformly between H and 
O, Fig-. 2. There is, therefore, a total fall from the under edge 
or lip of the measuring outlet to the end of the open chamber of 
3"93 inches ; or — as the length is 17'72"feet — very nearly 1 inch 
in 54. When the water reaches O, it enters the channel of dis- 
tribution, and becomes the property either temporarily or per- 
manently of the parties to whom the grant of it has been made. 
Arrangements at O vary. Sometimes there is a fall from the 
end of the modulo to the bed of the channel ; but generally the 
two are on the same level, the latter being carried forward at the 
usual slope for such works. 
" From the preceding details, it therefore appears that the 
modulo macjistralc, in its normal form, has a length of nearly 
37|- English feet, and a breadth variable according to the 
quantity of water it is designed to measure. If a single ' water- 
inch,' for example, be the volume, the breadth of the covered 
chamber would be 25 "54 inches, and that of the open chamber 
13'75 at its upper, and 25"54 at its lower extremity. The floor- 
ing of the former rises 15*72 to the rear, while that of the latter 
falls 3'93 in the same direction. 
" It is essential to the effective operation of the regulating sluice 
in the modulo magistrale, that there should be a difference of level 
between the water in the canal and in the apparatus of at least 
7"86 inches ; and as the height of water in the latter must be 
27'51 inches, the depth of water in the canal of supply must 
necessarily be not less than the sum of these numbers, or 35'37, 
being very nearly 3 feet. In this case the relative heights of 
different parts of the works are given below, the bottom of the 
canal of supply being the zero line. 
^'■■^ " English inches. 
" Bottom of the canal 0-00 
Level of the water in th.e canal 35"37 
Level of the water in the interior of the modulo giving the | f>--5i 
constant pressure l' " * 
Le\ el of under surface of tlie stone slab at the mouth of the 
covered chamber, and of the upper edge of the measuring , 23-5S* 
outlet 
Level of lower ed<;e of measuring apparatus at the end of thel , 
ramp of the flooring of the covered chamber / ' 
Level of the flooring at the head of the open chamber .. 13"75 
Level of the flooring at the termination of the open chamber 11"79." 
In Sardinia a rule for the water measure is prospectively pre- 
scribed in the G43rd Article of their Civil Code. For the details 
of their plan, I must refer the reader to Colonel Baird Smith's, 
work, remarking that custom there so much overrides the law, 
that in the canal of Caluso " there is scarcely an outlet in Avhich 
the prescribed limits are observed;" and that a practice of 
