_Of_ Aqueducts.
[Sidenote: _Lib. 8. Chap. 6._]
In Order to the bringing of Waters to Towns and Cities, the Level must
be exactly taken; to the end, it may be known whether the Waters can be
brought thither or no. The Ancients to this end made use of an
Instrument called _Corobates_, which was directed by a Lead, and by
Water, when the Wind hindered them from making use of the Lead.
They brought their Water three several ways; _viz._ by _Aqueducts_, by
Pipes of Lead, and Pipes baked in a _Potter's_ Furnace. They allowed for
the _Channels_ or _Sewers_ of the _Aqueducts_, for every 100 Foot, half
a Foot of Declination or Sloping; and if any Hills were in their way,
they dug through them, making Vents to give Air at convenient Distances.
The Pipes of Lead were at least 9 Foot long; they made them of bended
Sheets or Plates, and of different thicknesses, according to the
Proportion of the greatness of the Pipes; these Pipes had likewise their
necessary Declination or Sloping, and if any Valley was in the way, they
made it equal to the Level with a Wall; they likewise made many Vents,
to give the Water Air, and to know where to mend the Pipes.
The Pipes of _Potter's-Work_, were two Inches thick; they were joyned
together with Mortar mixed with Oil, and when they had _Conde_ or
_Joynt_ to make, they made use of a red Free Stone which they pierced
through, to receive the two Ends of the Pipes.