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let it be laid according to the slope of the hill, and when
it arrives at the bottom, let it be carried level by means
of à low substruction as great a distance as possible;
this is the part called the venter, by the Greeks «oa;
when it arrives at the opposite acclivity, the water therein
being but slightly swelled on account of the length of
the venter, it may be directed upwards. If the venter
were not made use of in valleys, nor the level substruc¬
tion, but instead of that the aqueduct were brought to
an elbow, the water would burst and destroy the joints
of the pipes. Over the venter long stand pipes should
be placed, by means of which, the violence of the air
may escape. Thus, those who have to conduct water
through leaden pipes, may by these rules, excellently
régulate its descent, its circuit, the venter, and the com
pression of the air. It will moreover be expedient, when
the level of the fall from the spring is obtained, to build
reservoirs at distances of twenty thousand feet from each
other, because if damage occur to any part, it will not
then be necessary to take the whole work to pieces, and
the defective places will be more easily found. These
reservoirs, however, are not to be made on a descent.
nor on the venter, nor on a rise, nor, generally speak-
ing, in valleys, but only on plains. But if the water
must be conveyed more economically, the following means
may be adopted. Thick earthen tubes are to be pro-
vided, not less than two inches in thickness, and tongued
at one end, so that they may fit into one another. The
joints are then to be coated with a mixture of quick lime
and oil, and in the elbows made by the level part of the
venter, instead of the pipe, must be placed a block of
red stone, which is to be perforated, so that the last
length of inclined pipe, as well as the first length of
the level part may be received into it. Then, on the op
posite side, where the acclivity begins, the block of red
stone receives the last length of the venter, and the
first length of the rising pipe. Thus adjusting the
direction of the tubes, both in the descents and acclivi-