Archimedes Texts

232
order to break the Fury of the Waves, that
not finding any Thing to beat against
with their whole Strength, they may fall back
gently and not with too violent a Precipitation.
Thus the Wave which is upon Return will
meet that which is coming on, and deaden its
Force. The Mouths of Rivers seem to be of
the same Nature with the Port, as they afford
Shelter to Vessels against Storms. They ought
therefore to be fortified and made narrower to
exclude the Fury of the Sea. Propertius says,

IT is the same in this Case; for the Mouths
of Rivers by the incessant Attacks of the Sea
are either overcome and filled up with Sand;
or else by a constant and obstinate Resistance,
they conquer and keep their Passages clear.
For this Reason it is an admirable Method to
open the River a double Discharge into the
Sea by two different Branches, if you have but
Water enough to supply them; not only that
Ships may be able to get in at one of them,
though the Wind be contrary for the other;
but also that if one of them be stopt up, either
by some Storm at Sea, or by some strong
Wind blowing into it, in such a Manner that
the Land-floods would be driven back again
into the Country, they may have another Pass
age open to discharge themselves into the Sea.
But of this enough. The next Point is how
to clean a River. Cæsar took a great deal of
Care about cleaning the Tyber, which was stopt
up with Rubbish, and there are vast Heaps of
the Stuff that was taken out still to be seen not
far from the River, as well within the City as
without. By what Methods he got so much
Rubbish out of so swift a River, I do not re
member to have read: But I suppose he made
use of Frames to shut out the River and then
emptying the Water out of them, he might
easily take out the Rubbish. These Frames
are made in the following Manner: Prepare
some strong Timbers cut square, with Grooves
cut in the Sides of them from Top to Bottom
four Inches deep, and in Breadth equal to the
Thickness of the Planks which you intend to
use in this Work; and prepare your Planks al
so of equal Length and Thickness with one
another. Having got these Things ready,
drive down your Timbers so as they may stand
perpendicular, at Distances from each other
equal to the Length of your Planks. When
your Timbers are well fixed, let your Planks
into the Grooves and drive them down to the
Bottom. Our Workmen call these Frames
Cataracts. Go on in the same Manner to fill
up the Spaces between the Timbers with Planks
and drive them as close together as possible.
Then go to work immediately with your
Pumps, Syphons, Buckets and all your other
Implements for emptying out the Water, put
ting on as many Hands as you can, and labour
ing without Intermission till you have thrown
out all the Water within your Inclosure. If it
leaks in any Part, stop up the Crack with any
old Rags: And thus the Business may be done.
Between this Frame and that which we men
tioned as necessary in the Building of Bridges,
there is this Difference; that the latter must be
stable and lasting, being to stand not only till
the Piers are built, but even till the Super
structure is settled; whereas this is only tem
porary, and as soon as the Dirt is got out to be
presently removed to another Place. But I
advise you, whether you clean your River by
the Help of this Frame, or by turning the
Course of the Water, that you do not pretend
to strive against the whole Force of the Stream
at a Time in any one Place, but go on Step by
Step and by Degrees. All Works raised against
the Violence of Waters, if they are made in
the Form of Arches, with their Backs turned
against the Weight of the Water, they will be
able to make the stouter Resistance. You may
level a Torrent or Water-fall by laying a Bar
rier across the Stream in such a Manner that the
Water is obliged to rise a good deal higher
than usual: For the Water running over from
the Top of this Barrier, will dig up the Ridge
in the Channel by its fall; and then even the
Channel above the Torrent, quite to the Spring
will be levelled in Proportion to the lower
Part of the Channel; for the Water in its De
scent will be continually moving and carrying
away the Earth. You may clean your Chan
nel by turning Oxen into it in the following
Manner: Stop it up that the Water may swell;
then drive your Cattle about in it so that they
may disturb all the Mud, and then opening the
Stream that the Water may pour in rapidly, it
will wash and carry away all the Dirt. If any
thing lies buried and fixed in the Stream so as
to spoil the Navigation, besides the common
Machines used by Workmen for removing such
Obstructions, it is a very good Method to load
a Barge deep, and to it fasten with Ropes the
Impediment which you would pull up: Then