Mark Sims wrote:

Did you make a typo...  or is clepsydra a real word?

:-) (just joking)

According to Donald DeCarle's Watch and Clock Encyclopedia:

Clepsydra-  Water Clock.  There are various types of water
clocks, from the plain vessel with an orifice at its base through
which water percolates and, by the lowering of the surface
of the water the passage of time is denoted, to the water clock
with a mechanical device to cause a hand to rotate.  The mechanical
clepsydra shown overleaf is simple in operation.  The cylindrical
vessel is slowly filled with water and a float with a stem and rack
engages the wheel to which the hour hand is attached.  As the vessel
fills so the float rises and the hour hand is made to rotate.  When
the vessel is full it is emtied (sic) and the process starts over
again.  While this type of clock is spectacular and one would like
to think it is of ancient origin, it has to be recorded that no
ancient example has been handed down to us.  On the other hand,
Egyptian water clocks, as illustrated, have been found and date from
about 1400B.C.  Primitive water clocks of Saxon times have been
found in the British Isles.  They are of the "sinking bowl" type,
where a bronze bowl with a hole in the bottom was placed upon the
surface of the water, water percolated through the hole and
eventually it sank which denoted a period of time.  It is
interesting to note that this system is still used in Algeria for
timing periods of the supply of water for irrigation purposes.

-Chuck Harris

Rex wrote:

Oh. I see!  It was already a joke that I didn't get.
Thanks.

Chuck Harris wrote:

Quoting Chuck Harris cfharris@erols.com, on Tue 29 Jul 2008 07:05:10 PM PDT:

I should note that because the flow is a function of the viscosity of
the working fluid, the clepsydra has a very nonlinear temperature
coefficient (with a saturation at around 0C and another saturation at
around 100C, if the working fluid is water, depending on the
atmospheric pressure) although this can be compensated to a certain
extent by changing fluids.. Is a clepsydra using, say, alcohol or
fluorinert(tm) still a clepsydra?

I wonder if one could make a temperature compensated one (where the
orifice size changes with temperature.. much like building a
temperature compensated pendulum using metals with two different CTE)

There are various forms with tipping bucket (like rain gages) that one
might be able to make a calendar with (raising the prospect of
actually having a leak second)