  Nearly 150 years ago, Lord Kelvin proposed the isotropic helicoid, a particle
with isotropic yet chiral interactions with a fluid, so that translation
couples to rotation. An implementation of his design fabricated with a
three-dimensional printer is found experimentally to have no detectable
translation-rotation coupling, although the particle point-group symmetry
allows this coupling. We explain these results by demonstrating that in Stokes
flow, the chiral coupling of such isotropic helicoids made out of non-chiral
vanes is due only to hydrodynamic interactions between these vanes. Therefore
it is small. In summary, Kelvin's predicted isotropic helicoid exists, but only
as a weak breaking of a symmetry of non-interacting vanes in Stokes flow.
