I'm not an authority on clepsydra, but I can pass along a couple of tidbits.
First, you'll have to define what you mean by "Clepsydra." A. J. Turner (see below for reference) defines four types, plus some exceptions. The four types he lists are:
- - outflow clepsydrae
- - inflow clepsydrae (plus sinking-bowl clepsydra)
- - continuous flow scoop-wheel clepsydrae (I think he includes Su Song's escapement here)
- - compartmented cylinder clepsydrae
Ancient clepsydrae were outflow or inflow. The inflow was, I think, considered a bit more accurate. This is because when fitted with an overflow in the feeding tank, a constant head of water could be maintained.
Turner wrote a book as a part of the "Catalog of the Collections" of The Time Museum in Rockford, Illinois. Though it does catalog these collections, it also has quite a bit of information on the clocks themselves. I'm never quite sure of the exact title of this book, though it is sitting before me as I write. The full title is, sort of: The Time Museum Catalogue of the Collections Volume I: Time Measuring Instruments Part 3: Water-clocks, Sand-glasses, Fire-clocks It's by A. J. Turner, published by The Time Museum in 1984. It's expensive, though ($95 if memory serves). Available from them at: The Time Museum Bookstore The Time Musuem 7801 East State St. Rockford IL 61125-0285
The clock designed by John Wilding is of the compartmented cylinder type. As Alan noted, the how-to booklet on this is available from Bill Smith (WRSmith2@aol.com). Though Wilding's design is "modern" in the sense that it uses plexiglass, it is actually related to quite a bit of medieval technology, especially to to many ideas about perpetual motion (all futile, of course). - Ord-Hume's book on perpetual motion covers the history of many of these. (I can dig up this reference if you need it.)
Turner's taxonomy also includes "exceptions," and that's where things can get very interesting indeed. The Earl of Meath used water in his clock (which is not really a "clepsydra") - both to impulse a "free" pendulum and in the striking "train." Charles K. Aked has done considerable original research into Meath's clock, and his publications in the NAWCC _Bulletin_ and in the now defunct _The Clockmaker_ should be consulted. I've done a description of Meath's clock (from secondhand sources, not firsthand observation) which is on a WWW page at: http://www.msen.com/~lemur/meath.html So far I've described the operation of the pendulum impulsing system. I hope one day to add a description of the striking train. All of the biblio references to Aked are given there as well.
The French physical chemist turned artist Bernard Gitton builds elaborate water clocks which use a water-impulsed pendulum (different than Meath's) and a system of calculating siphons (yes, really!) to display the time. I've also written up an account of his clocks, on http://www.msen.com/~lemur/gitton.html
If you're interested in ancient sources, there is a medieval Islamic manuscript entitled Kita/-/b Arshimi/-/das fi `amal al-binkama/-/t (where the /-/ means put a line over the preceeding vowel) that describes the construction of a clepsydra as well as elaborate automata driven by it. This book was traditionally attributed to Archimedes, and although it is certainly the work of several authors, its translator, D. R. Hill, thinks that some of it may in fact derive from Archimedes. This has been translated by Donald Routledge Hill and was published as: _On the Construction of Water Clocks_, Turner &Devereux Occasional Paper No. 4, 1976. The NAWCC Library might be of assistance in helping you research this document. Hardly a construction manual, though.
This same D. R. Hill has written _A History of Engineering in Classical and Medieval Times_. La Salle, Illinois: Open Court, 1984. ISBN 0-87548-422-0. A very good study, though it covers the "Archimedes" clock in less detail.
On another ancient thread, Joseph Needham has done a rather well-known reconstruction of a water-based escapement on a Chinese clock by Su Song dating from 1088-92. There's a picture of a working model of this in the Turner/Time Museum book; references to this one are fairly easy to find.
There's also a town in Canada that has a large public clepsydra on display - and a WWW site featuring this. The URL is: http://www.valleyweb.com/middleton/clock.html
The town is Middleton, Nova Scotia. From the illustration, it appears to be an inflow clepsydra of some sophistication. It uses a siphon to automatically empty the float tank, and there is some device on the feed tank that looks a bit like an inverted version of the feedback mechanism on the "Archimedes" clepsydra. Not sure about this, though - it could simply be a device for adjusting the level of the water in the feed tank. Their page indicates that there were, in 1991, two other water clocks on public display in North America. These would almost certainly have been the Gitton clocks at the Children's Museum, Indianapolis and at The Time Museum in Rockford, IL. The clock in The Time Museum is no longer there, and The Time Museum is unable to give any information as to its location (it was the prototype of Gitton's 2.4 meter series of clocks); Gitton indicates that he thinks that it may currently be in England.
There's a gif of an engraving of a clepsydra (no source given) through: http://www.perseus.tufts.edu/GreekScience/Students/Jesse/Bibliography.html
As you'll soon see, each of us on this list has a specialty. I'm the one who posts references to lots of books without ever actually offering any concrete answers... I would suggest, though, that a couple of questions to the list might help you design one. So:
- What are the best ways to prevent such a device from fouling with a) minerals, b) microscopic friends? (Most sources I've read say that such fouling is the biggest impediment to accurate timekeeping with clepsydrae. I suppose this rules out keeping goldfish in the supply tank.)
- Is there any way to determine the size of an opening one needs in a vessel of some given size to get a certain flow rate?
- Outflow clepsydrae have variable water levels, and so were constructed (even way back by the Egyptians) with flaring (conical) sides to compensate - how would one calculate this flare?
Hope this helps David M. MacMillan dmm@lemur.com http://www.msen.com/~lemur/
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