—13 
bution, so that each will be given the water long enough to 
give each the same quantity. This would give a short time 
for the periods when the water is plentiful, and longer times 
when low. The unit could be varied, so as to bring the irri¬ 
gations a convenient time apart. The successful operation of 
such a system would require an intelligent superintendent, 
and one who had the confidence of the users of the water, or 
a wide-spread knowledge among the users. 
In the distribution of water from small reservoirs, where 
there are but few interested, and where the different owners 
do not care to use the water at the same time, some such ar¬ 
rangement is necessary. With the weir measurement it is 
possible to keep account of the amount used by each person, 
so that the water may be divided in proportion to the rights 
of each. 
MODULES. 
It is not possible to secure a module satisfactory in every 
respect or to meet all conditions. Where there is fall to 
spare in the ditch some forms are available which would be 
excluded if there were no fall to spare. 
The features desired in a module may vary under differ¬ 
ent conditions, so that there are some forms which give ex¬ 
cellent satisfaction in some circumstances, which do not in 
other cases where the conditions emphasize the desirability 
of some other feature. In the early stage of water measure¬ 
ment, when water is abundant, accuracy is a minor consider¬ 
ation, while with increased demand for water, it is one of the 
first, if not the first consideration. A second desirable fea¬ 
ture, which has been the object toward which many have 
worked, is a module which is self-regulating and preserves 
the same discharge of water even with fluctuating depths of 
water in the canal. 
The following may be considered desirable conditions in 
a module. Most of these conditions were recognized several 
centuries ago by the magistrates of Milan: 
*1. Its discharge should be capable of being converted 
into absolute measure—as into cubic feet per second. 
*2. The ratio indicated by the module between the dis¬ 
charges from two outlets should be thejsame as the actual ratio. 
*3. The same module or box should give the same 
amount of water wherever placed. 
4. It should be capable of being used with large or small 
canals. 
*5. It should be capable of being set to discharge any 
fraction of its capacity, so as to be capable of distributing 
water pro rata. 
