# How does the Hydra Lamp "Anti-Gravity Fountain" work? **URL:** \ **Category:** Factual Questions\ **Created:** [July 20, 2019, 2:44pm UTC](https://boards.straightdope.com/t/how-does-the-hydra-lamp-anti-gravity-fountain-work/837350 "2019-07-20T14:44:25Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [July 20, 2019, 2:44pm UTC](https://boards.straightdope.com/t/how-does-the-hydra-lamp-anti-gravity-fountain-work/837350/1 "2019-07-20T14:44:25Z")
How does the Hydra Lamp work? If you haven’t seen it yet, it’s a newish consumer device in which water drops flow or appear to flow slowly upward. See a video of a cat interacting with the device [here](https://vimeo.com/331109031). Their website [FAQs](https://www.hydralamp.com/apps/help-center#!hc-how-does-hydra-lamp-work) say only that “The Hydra Lamp uses accurately timed lighting to create an anti-gravity effect.” That doesn’t provide enough detail to satisfy my curiosity. ---
**Author:** ![Max\_S](https://avatars.discourse-cdn.com/v4/letter/m/46a35a/32.png) [@Max\_S](https://boards.straightdope.com/u/Max_S)\ **Post date:** [July 20, 2019, 2:59pm UTC](https://boards.straightdope.com/t/how-does-the-hydra-lamp-anti-gravity-fountain-work/837350/2 "2019-07-20T14:59:32Z")
Is this similar to the trick used in Now You See Me 2? Where they have water dropping really fast, but shine lights on the droplets at just the right time that you see it going backwards; a variation of the stroboscopic effect. ~Max ---
**Author:** ![brossa](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/brossa/32/3040_2.png) [@brossa](https://boards.straightdope.com/u/brossa)\ **Post date:** [July 20, 2019, 2:59pm UTC](https://boards.straightdope.com/t/how-does-the-hydra-lamp-anti-gravity-fountain-work/837350/3 "2019-07-20T14:59:54Z")
It’s sputtering out discrete drops of water at a fixed rate; we’ll say 10 per second as an example. They illuminate the drops with a strobe light, which tricks your eye into only attending to the brightly lit intervals and ignoring the periods in between the strobe flashes when then drops continue to fall. If they hit the strobe at 10 flashes per second, you will see the drops appear to hover in midair - they don’t actually hover, of course. With each flash, a drop has moved from one position to the next one down, and been replaced by the following drop. The drops look identical, though, so you think the same drop is staying at one spot the whole time. Under bright enough ambient light the effect would be lost. To make the drops climb or fall slowly, just detune the strobe slightly, to say 10.1 flashes per second. Now each drop falls just a bit more per flash, so the whole train seems to be gliding downward. ---
**Author:** ![MindsEye\_Watering](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mindseye_watering/32/3619_2.png) [@MindsEye\_Watering](https://boards.straightdope.com/u/MindsEye_Watering)\ **Post date:** [July 20, 2019, 3:03pm UTC](https://boards.straightdope.com/t/how-does-the-hydra-lamp-anti-gravity-fountain-work/837350/4 "2019-07-20T15:03:03Z")
It uses a strobe light. Very fast light pulses that look like steady light, but are not. ---
**Author:** ![Max\_S](https://avatars.discourse-cdn.com/v4/letter/m/46a35a/32.png) [@Max\_S](https://boards.straightdope.com/u/Max_S)\ **Post date:** [July 20, 2019, 3:03pm UTC](https://boards.straightdope.com/t/how-does-the-hydra-lamp-anti-gravity-fountain-work/837350/5 "2019-07-20T15:03:46Z")
See this video: [The Strobe Light Effect (Levitating Water Experiment) - YouTube](https://www.youtube.com/watch?v=TH1mJpOnxDE) ---
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [July 20, 2019, 3:12pm UTC](https://boards.straightdope.com/t/how-does-the-hydra-lamp-anti-gravity-fountain-work/837350/6 "2019-07-20T15:12:10Z")
Thanks, folks. That makes sense. I should have thought of it myself, because now that you mention the strobe effect, I do remember the old Straight Dope column that discusses it: [How come the wheels of a moving car appear to rotate backward sometimes?](https://www.straightdope.com/columns/read/730/how-come-the-wheels-of-a-moving-car-appear-to-rotate-backward-sometimes/) ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [July 20, 2019, 3:34pm UTC](https://boards.straightdope.com/t/how-does-the-hydra-lamp-anti-gravity-fountain-work/837350/7 "2019-07-20T15:34:33Z")
It’s not only motion that is distorted, but so is energy. When the cat gently taps a drop it breaks up and flies off a lot faster that one would expect for such a seemingly slow moving thing. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 20, 2019, 3:48pm UTC](https://boards.straightdope.com/t/how-does-the-hydra-lamp-anti-gravity-fountain-work/837350/8 "2019-07-20T15:48:20Z")
Or rather, the (appearance of) energy isn’t distorted at all, despite the extreme distortion of the (appearance of) motion. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [July 20, 2019, 10:05pm UTC](https://boards.straightdope.com/t/how-does-the-hydra-lamp-anti-gravity-fountain-work/837350/9 "2019-07-20T22:05:44Z")
What is distorted _is_ the appearance. I felt no need to include extra words.