Not long ago, I had an interesting lunchtime discussion with Job Vranish. I don’t recall exactly how we got on the topic, but we were discussing how mesmerizing siphons are. As the discussion progressed to imagining a fluid-based computer (that’s another story…), I remembered something I had seen as a child at the Indianapolis Children’s museum: an immense clock that kept time with the flow of water through glass tubes.
Later, I did some research into what I discovered is one of the largest water clocks ever made by the French physicist-turned-artist, Bernard Gitton.
Gitton’s water clock begins, as many clocks do, with a pendulum. This pendulum is attached to a small scoop into which a constant stream of water flows. As the pendulum swings, the scoops spills its contents into another vessel at regular intervals.
These “dollops” of water must then be transformed into the displayed minute and hour values along the sides of the clock.
First, the dollops drain from the collection vessel down a piece of glass tubing where they settle into the “trap” of an S-shaped siphon. The siphon is calibrated such that multiple dollops collect before the siphon triggers, suctioning the entirety of the contents down into the next component. These siphons are triggered when the fluid reaches the height of the top of the S-shaped curve and begins to be pulled downward by gravity. Once this process begins, the fluid continues to drain from the siphon until it is empty.
In the case of Gitton’s water clock, the fluid drains into a series of additional siphons, calibrated to hold increasing volumes of water before triggering. These siphons act as frequency dividers for the initial signal provided by the pendulum. (i.e. If a dollop comes every two seconds, and the first siphon can hold three dollops, then the first siphon will drain only every 6 seconds, the second siphon in the series may hold several of these larger dollops, dividing the frequency still more, and so forth.)
The last siphon in the series has a very interesting property – the low pressure created by draining of the vessel is “captured” by a sort of “vacuum locking” device that keeps the “vacuum” from “traveling” back up the input channel. Instead, the lower pressure is carried by another piece of tubing over to a vessel with a siphon on the brink of draining. (Just how this balance is calibrated is not clear to me.) When the “vacuum locked” siphon triggers and transfers this lower pressure to the other vessel, it triggers that siphon and drains the fluid into the minutes counter.
This minutes counter is a column of stacked globes that contain the colored fluid. The height of the fluid in the column fills a number of the globes corresponding to the minutes past the hour. Alongside the column of minute-globes is another S-shaped siphon that triggers just before the hour, draining the entire column and triggering another vessel to drain into the hours column. This process takes several minutes, during which the observer has the distinct impression that time itself is being lost down the drain. The Greek idiom used to refer to water clocks is “Clepsydra”, which translates more literally to “water thief”. Gitton calls these clocks (of which there are several around the world), Time-Flow Clocks or “Horloges à voir le temps couler” (roughly translated: clocks for viewing the passing of time).
If you’re as fascinated by this device as I am, you can read more at this page, put together by David M. MacMillan, where you can find a much more detailed technical explanation along with a number of helpful diagrams. I also recommend watching the fantastic nine minute documentary, Bernard Gitton – Physics and Art, done by Michael Magee. Another explanation of the water clock, produced by The Children’s Museum of Indianapolis, can be viewed on YouTube. There are a few other videos on YouTube of these water clocks in operation, but most of them are not very clear. You can get a better sense of what is happening by watching this intricately animated illustration created by Roland Barth. Additionally, Gitton’s studio has a small webpage with contact information at www.bernard-gitton.com. (You may need to scroll sideways to reach the content in the frames on the Gitton site.)
What beautiful artifacts inspire you? If you have children, do you try to expose them to things that inspire? What feats of engineering are still impressed upon your memory from childhood?
Edit 2013-06-25: David M. Macmillan’s site appears not to be accessible anymore. I’ve updated the link to point to a copy from the Internet Archive retrieved in March.