, travelling carriages, drums, mills, screws, scorpiones,
ballistae, pressbeams, and all other machines, produce the results
intended, on the same principles, by turning about a rectilinear axis
and by the revolution of a circle.

CHAPTER IV

ENGINES FOR RAISING WATER

1. I shall now explain the making of the different kinds of engines
which have been invented for raising water, and will first speak of the
tympanum. Although it does not lift the water high, it raises a great
quantity very quickly. An axle is fashioned on a lathe or with the
compasses, its ends are shod with iron hoops, and it carries round its
middle a tympanum made of boards joined together. It rests on posts
which have pieces of iron on them under the ends of the axle. In the
interior of this tympanum there are eight crosspieces set at intervals,
extending from the axle to the circumference of the tympanum, and
dividing the space in the tympanum into equal compartments.

2. Planks are nailed round the face of it, leaving six-inch apertures to
admit the water. At one side of it there are also holes, like those of a
dovecot, next to the axle, one for each compartment. After being smeared
with pitch like a ship, the thing is turned by the tread of men, and
raising the water by means of the apertures in the face of the tympanum,
delivers it through the holes next to the axle into a wooden trough set
underneath, with a conduit joined to it. Thus, a large quantity of water
is furnished for irrigation in gardens, or for supplying the needs of
saltworks.

3. But when it has to be raised higher, the same principle will be
modified as follows. A wheel on an axle is to be made, large enough to
reach the necessary height. All round the circumference of the wheel
there will be cubical boxes, made tight with pitch and wax. So, when the
wheel is turned by treading, the boxes, carried up full and again
returning to the bottom, will of themselves discharge into the reservoir
what they have carried up.

4. But, if it has to be supplied to a place still more high, a double
iron chain, which will reach the surface when let down, is passed round
the axle of the same wheel, with bronze buckets attached to it, each
holding about six pints. The turning of the wheel, winding the chain
round the axle, will carry the buckets to the top, and as they pass
above the axle they must tip over and deliver into the reservoir what
they have carried up.

CHAPTER V