—28— 
feit or^feSt. USCd in thC COmputation ’ is -* 6 le “ than 10 
deDthVwi>h e t-h^ at the e . ffecti Y e . le ngth varies with different 
depths with the same weir. It is because of this, that of two 
tlrn tl? ne tW ' Ce ,, aS lon ? as the other - of the rectangular pat¬ 
tern, the one will not give exactly twice as much as the other 
even for the same depths. But if the two have their effec- 
nl^ ng iii, S ? t - hat ? ne 'Vu ice the other ’ then the discharge 
or one will be twice that of the other. ® ; 
T he ^‘PP 0 , 1611 ' weir is a form adopted in order that the 
lengdTof the g weir. are C ° nStant,y the same as the measured 
nr , The weir here called the Cippoletti weir because of its 
ditfon lEt 'b't. ° ne Proposed by Cippoletti to meet the con- 
ditions which the Italian government laid upon the company 
which was given a'concession of water for the Canale Villo- 
buib a h f 6 aSt ° f tHe great ^ alian canals. This canal was 
lb „‘ i ew years since as a “high line” canal to water land 
above the existing canals. It waters about 12s,000acres be- 
Milan th f Tb Cin ° a b d Adda • riverS ’ ^ ust north of the city of 
rpn!L u, k aCt ofconcesslon to this canal, the government 
menT!n he ?° m ? any to Propose a module for the measure- 
ment and sale of water which should be based upon the 
theory of the weir with free fall, and that the module should 
be accurate. 1 he problem was put in the able hands of 
The a nrnKl 1PP °^ tU ’ , the - engineer in charge of construction. 
1 he problem Cippoletti proposed to himself, was, while ore- 
mnb n f A ® lmp . le a " d convenient form- of the Francis for- 
muia, to determine the form and condition of the weir so that 
v P rl S n C S arg !i, Sh0 “ d ’ be , proportional to the length of the 
weir, and so that no single cause should produce an error of 
more than one half of 1 per cent. 
a nJ a ^ ng fi t ^ eX ? erime ! lts made by Fr ancis as a basis, he 
attempted first to determine a form of the weir in which the 
contractions at the sides should be automatically overcome. 
i~\ f , 1, . r weir, as already mentioned, the effect 
?f tbe contraction increases in proportion to the depth. The 
‘l; a SUg ?u S ted itself to him, that by making the form of the 
Inl tfiil 13 th i e are u mc r eases b .y an amount in propor- 
1 le depth on the weir, then if the increase in area can 
s ° as exactly balance the loss due to the contrac- 
on, the flow through the weir would remain the same as 
though the weir were rectangular, of the same length of sill, 
, p U n T ,th °m cont raction. In other words, the effective 
2 ‘f °" 1(l remain the same for all depths. Manifestly, a 
a trapezoidal shape, like that in Figure 7 presents the 
