John Walker, the author of this and host of Fourmilab, passed away last year: <a href="https://news.ycombinator.com/item?id=39297185">https://news.ycombinator.com/item?id=39297185</a>
A caveat.
I had the change to perform a similar experiment at work testing very sensitive accelerometers. Believe it or not, the biggest source of errors was the bending of the floor due to the test masses!
A better setup would be to suspend the spheres exactly like the tuna cans, and test two configurations rotated by 90 degrees.
> This is the consequence of all the forces of physics being gauge invariant: absolute values don't exist—only differences matter<p>there's something about this quote that i really like, going to have to use it out of context on people
I’m on my second attempt at this. The first worked but it was unwieldy and kind of unsatisfying. I’m going to make a second attempt using a bearing of ferrofluid, which has a damping effect, and use field alignment with the earths magnetic field as the source of torque. It’s really fun and at times frustrating trying to eek out effects of nanonewtons of force, highly recommended.
Another interesting way to see the effects of gravity can be done with pendulums, using a Vening Meinesz apparatus.<p>It's not as spectacular as seeing a torsion bar move, but it's more sensitive.
I did this one in the senior lab as an undergrad studying physics at New Mexico Tech.<p>I got to use a whole gymnasium for a weekend and used a laser beam projected across the gym to read out the torsion balance. Pretty cool that you can measure the gravitational constant [1] so easily, if approximately.<p>[1] <a href="https://en.wikipedia.org/wiki/Gravitational_constant" rel="nofollow">https://en.wikipedia.org/wiki/Gravitational_constant</a>
I ran out of time to finish reading the article. He explained the importance of using a camera to observe the results due to the ways a human presence would interfere with the experiment.<p>When he talks about how Archimedes might have reproduced his device using technologies of the time, did he address what historic alternative might take the place of the camera?
Fun fact. Charles Mason and Jeremiah Dixon, using theodolites, plumb bobs, and spirit levels, were able to detect variations in gravity from the local environment in 1767. Upon completing the resurvey on the way back to Philadelphia, they noticed a systematic error and concluded it was because of gravitational deflection due to the Allegheny mountains (with the help of Maskelyne, Cavendish and the Royal Society).<p>Sometimes I think about that and it just blows me away.
I miss John, this has much of the charm of the old "Amateur Scientist" columns from Scientific American. I remind myself from time to time that so much great work has been done by scientists with simple hand tools and a thoughtful experiment.
> The reason lies in the extraordinary weakness of the gravitational force.<p>I recall reading Brian Greene giving the example of sitting in a chair. The molecules of the chair are stronger than gravity. You're not crashing through to the floor.
Reminds me a bit of Greg Egans' Incandescence [1]<p>[1] : <a href="https://en.wikipedia.org/wiki/Incandescence_(novel)" rel="nofollow">https://en.wikipedia.org/wiki/Incandescence_(novel)</a>