Tym′pa-num.
1. (
Hydraulic Engineering.) An ancient form of wheel for elevating water.
Its original form was like that of a drum, whence its name.
It was a cylinder with radial partitions and small openings in the periphery, which admitted a certain quantity of water into the chambers thus formed as those portions of the periphery came in turn to be submerged.
As the wheel revolved, such portions of water were carried up and flowed along the partition toward the axis around which the water was discharged, being elevated to a hight nearly equal to the radius of the wheel.
The wheel was driven by floats on the periphery or side of the wheel, or by means of animal or manual power, and had several modifications.
The Roman form of the
tympanum is described by
Vitruvius, 50 B. C., and was derived from
Egypt.
The partitions were 8 in number, and were radial; the holes, 6 inches in diameter, were made in the drum-like, cylindrical surface, which was otherwise closely boarded up; the wheel was mounted so as to rotate over the side of a vessel which was moored, and was driven by a
tread-wheel on board the vessel; the water lifted by the buckets was discharged at the axis of the wheel.
What is known as
De la Faye's pump is constructed on this plan.
This wheel is often called the
Persian, and this may be correct, geographically speaking; but for perspicuity, the term
Persian should be applied to a wheel with boxes, pots, or buckets which are attached to the wheel, on or near its periphery.
The
Noria wheel of
Palestine is, perhaps, a true example of the
Persian wheel.
See Norin.
In process of time this highly useful wheel, so much used in
Oriental countries in raising water for irrigation, was improved by removing the exterior surface from which it derived its name, the buckets being made scoop-shaped.
Such was the form used by
Perronet, at Orleans Bridge, about 1750.
In
Fig. 6845,
a is a section.
and
b an end elevation of this wheel.
It had curved buckets, and raised the water 8 feet. Its effectiveness varied with the depth to which its circumference dipped into the water.
At 1 foot submergence, 12 men, relieved every 2 hours, gave 2 turns per minute: at each turn, 24 cells were emptied, each containing 1 1/2 cubic feet, giving, for the hour, 4.320 cubic feet of water raised 8 feet high; this was conveyed by the spiral buckets to an annular discharge-chamber around the axis of the wheel.
The comparison of effectiveness was as follows :—
| Submergence. | Revolution per hour. | Cubic feet raised. |
| 12 inches. | 120 | 4,320 |
| 9 inches. | 150 | 3,600 |
| 6 inches. | 180 | 2,880 |
| 3 inches. | 180 | 2,160 |
 |
|
Tympanum. |
A modification of the tympanum has spiral ducts leading to a discharge-chamber around the axis.
It is, or may be, propelled by the current.
This form of wheel has its advocates in all civilized countries, and is employed in draining some of the fluviatile districts in our Western country; for instance, at
Cairo, where a wheel of this character is, or was, driven by steampower, for removing the drainage of that rather low site, discharging it over the levee, which keeps back the waters of the river.
The
tympanum, under the name of the
scoopwheel, is much used in the drainage of the fens in the
East of
England.
The name is somewhat confusedly applied to wheels of the tympanum character, and to those with radial buckets which traverse in a chute.
These wheels, driven by
steam-engines, have, to a great extent, superseded the
Dutch windmills and pumps which have been used there for several centuries.
In one place, a steam-engine has superseded 44 windmills.
In another place, two
steam-engines, of 110 horse-power, drain 28,000 acres, and have superseded 75 windmills.
These very efficient wheels have a diameter a little more than double that of the elevation to which the water is required to be raised.
Some wheels deliver the water at the axis, and others have floats like an ordinary water-wheel, and merely traverse in a curved, inclined trough of masonry, which connects the lower with the upper level.
See scoop-wheel.
2. (
Architecture.) The triangular panel of the fastigium or pediment of any building, comprehended between its corona and that of the entablature.
The panels of a framed door were called
tympana by the Romans.
3. (
Music.) Another name for the tambourine.
See Plates LXXVI., LXXVII.,
Bonanni's “Istromenti Armonici,”
Roma, 1776.
The tympanum (Gr.
tympanon) was a hand-drum or tambourine, but covered with parchment, back and front.
It was used in company with various kinds of harps, lyres, and pipes, cymbals (
kymlala) of metal, the straight brass trumpet (
salpinx) and curved brass horn (
keras), the castanets
crotala) of wood and metal.
The drum is common among all uncultivated nations, and was a prominent feature in the ancient practice.
The
Egyptian musical instruments were harps, guitars.
single and double pipes, two kinds of trumpets, three of tambourines, three of drums, gongs, bells, cymbals, and castanets, the sistrum, maces, and bells.
The largest Assyrian band shown at Khorsabad has a leader with a harp, followed by two with a dulcimer and double pipe; these by two men with harps; then four women with harps;
[
2672]
one beating a drum and another with a double pipe.
Then comes a chorus of singers, clapping their hands
The
Hebrew drum (
toph) was a small hand-drum or
tambourine, called
timbrel or
tabret in the
English version;
vide Miriam and Jephtha's daughter.
The hand-drum of some parts of the
East is still called
doff, diff, or
adufe.
