
Pythagorean cup - heeton
http://en.wikipedia.org/wiki/Pythagorean_cup
======
analog31
Beautiful. This has a modern application. When fed with a slow trickle of
water, it will empty itself periodically, and formed the basis of automatic-
flush urinals before the electronic valves became commonplace.

~~~
nlawalker
Doesn't a flush require that water be added fast enough to eliminate all the
air from the bend? Otherwise, water will just trickle out at the same rate it
trickles in.

~~~
analog31
Yes, it has to do that. The bend may have to be narrow enough for surface
tension to have an effect.

I found this nice web page, the Virtual Lavatory:

[http://www.users.waitrose.com/~ttagrevatt/vlav/works_cistern...](http://www.users.waitrose.com/~ttagrevatt/vlav/works_cisterns.html)

~~~
jessaustin
Interesting, but goofy in spots:

 _Why did Britain evolve such a complex mechanism when this pattern seems so
simple? Water economy: these valves can leak and can be kept permanently open,
allowing precious gallons to be wasted._

I've never been to Britain, but my impression is that it's not a particularly
dry place. Why would "water economy" be so much more important there than in
e.g. Israel or California? Perhaps toilet technology is as path-dependent as
any other evolutionary process?

------
heeton
Just curious: I understand why titles might be reset to the raw title found on
the page, but in this case it's just made the headline less useful.

I added a tiny bit of context when posting - to explain to people why this
might be interesting to them. "Pythagorean 'greedy' cup - empties entirely if
filled too much".

What's the purpose of reducing that to just the raw wikipedia title?

~~~
tzs
Your added context worked for me. I saw your original title but did not have
time to read an article, but your title interested me enough that I noted to
myself to come back and read it later.

I would have skipped it under the current title.

~~~
heeton
Thanks, I thought as much. I certainly noticed that it got a lot of votes -
title changed - and it started to get much fewer upvotes, indicating that less
people bothered to read it.

~~~
tagawa
I was the same. I saw the full title in the morning and thought it looked
interesting enought to read later. When I came back the title had changed and
I wouldn't have clicked through had I not seen the explanation in the original
title.

Glad I did, too, because it's such a clever "gadget"!

------
ds9
My first thought was, wow, they could have had computers based on sets of
these connected in different ways, as logic circuits. As I recall from the
Stephenson version, Turing and co. were using something similar in the analog
days.

~~~
deutronium
Yup it's definitely possible
[http://en.wikipedia.org/wiki/Fluidics](http://en.wikipedia.org/wiki/Fluidics)

------
x1798DE
Clever, but isn't there some danger that if you tipped it the wrong way when
drinking out of it, even before the "gluttony" level, that you'd start up the
siphon action, causing it to empty out onto the floor? At the very least you
can imagine you'd get a bit of wine trapped in the curve, which would then
drip out of the hole at the bottom.

~~~
lmm
I don't think so, because the column is in the middle; as long as the tube in
the middle is narrow, whichever way you tilt it the height in the centre will
be the same as it was at the start and nothing comes out. I guess if you tilt
it past horizontal to drink out of while the cup's more than half full then
you have a problem - but that sounds more like a feature than a bug.

~~~
tgb
Yes, upon seeing this I immediately wanted a 'trick' cup that did this but had
this, umm, feature more hidden by placing it in the side of the cup not the
middle. But then an unsuspecting, but non-greedy, user may spill the entire
cup just by sipping out of the wrong side! The central column should make it
quite safe in comparison.

------
mankyd
Wouldn't it be easier to simply have a smaller cup? I mean, this is clever,
but seems a tad impractical.

~~~
GhotiFish
The point is to punish gluttony, but even that point isn't the point. The
point is to demonstrate a system with a threshold. a tank fills to a point,
and rather than overflowing the tank, completely empties it.

A more obvious subversion of this would be to stick your finger in the
discharge at the bottom. Fill it as much as you want then.

------
Robosprout
Here is a 3d printable version :) Work in progress...enjoy.

[https://drive.google.com/folderview?id=0BwATmn6QdbBYeFM1b2to...](https://drive.google.com/folderview?id=0BwATmn6QdbBYeFM1b2tocGcwX2M&usp=sharing)

~~~
Robosprout
[http://shapedo.com/robosprout/pythagorean_cup](http://shapedo.com/robosprout/pythagorean_cup)

BTW, shapedo has a tool to migrate all your thingiverse items over with one
click :)

------
jhgg
A good video explaining it:

[https://www.youtube.com/watch?v=4q9Jim1abMo](https://www.youtube.com/watch?v=4q9Jim1abMo)

~~~
daveid
That is a copy. Here is the original video from the original channel:
[https://www.youtube.com/watch?v=kb5N2wpYRJg](https://www.youtube.com/watch?v=kb5N2wpYRJg)

------
deutronium
I love this idea! I wonder if someone could make a 3D model that could be
easily printed of one.

------
warrenmar
This principle is used in aquaponics in the form of a bell siphon. You don't
want to keep the roots of your plans submerged for long periods of time, so
this lets you flush out the water automatically.

------
tokenadult
As noted on the article talk page, it's rather dubiously sourced that this
device really goes back to Pythagoras. The tourist wares shown in the article
photographs are of course much newer than that.

------
DougWebb
It seems unlikely that this would have been used as a drinking cup, because it
wouldn't work properly if it's moved around or tipped. Instead, it was
probably a "temple magic" device, where a worshipper would have to buy some
sacrificial wine and pour it into a mounted cup as a sacrifice. If they don't
pour enough in, nothing happens, but once they pour enough the god "drinks"
the wine. The wine probably fell down into a bucket attached to some mechanism
that would make noise, or move something, or maybe open a door, to indicate
that the god is satisfied with the sacrifice.

~~~
Retric
The water level in the center does not rise when you tip a cup. Sloshing back
and forth does the same thing the only edge case banging the cup on a surface
but given a small internal channel that's not going to do much either.

PS: My initial thought was incaseing the channel in the edge would be less
obvious but that would have more issues with tipping.

------
yitchelle
This cup seems like one of the trick cup that you give to your friends after
they had a few pints of beer.

Those Greeks, funny guys!

------
SilasX
Wouldn't it be easier to have the hole go straight up through the center shaft
without looping around?

~~~
arxanas
Then it would only remove the excess, not the entire contents.

~~~
SilasX
The linked design only removes the excess too.

~~~
arxanas
It seemed to me that the linked design removed the entire contents:
"Hydrostatic pressure then creates a siphon through the central column,
causing the entire contents of the cup to be emptied through the hole at the
bottom of the stem."

------
mrfusion
Is this how a regular toilet works too?

~~~
hcarvalhoalves
Yes, it's also based on communicating vessels and syphon effect.

------
scotty79
I implemented this design in LiquidSketch game on iPad some time ago.
Amazingly it worked.

------
jotm
Cool concept, though not very practical (just like so many other ideas).
Sounds like the Spork of it's time :).

------
stephenitis
"imbibe"
[http://monosnap.com/image/bdPaQiIKYaJ1Qpw19P9O2KZKcsEZyq](http://monosnap.com/image/bdPaQiIKYaJ1Qpw19P9O2KZKcsEZyq)

