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ID number:  BIRRC-P0208
Institution:  Research and Cultural Collections
Named collection:  Historic Physics Collection
Title / Object name:  Poynting’s quartz spheres for gravitational experiments
Object type:  Physics apparatus
Date made:  c. 1898
Materials:  Spheres of crystalline quartz on velvet covered base.
Measurements:  Largest sphere diameter 6.6 cm, mass 399.9 g Smallest sphere: diameter 0.9 cm, mass 1.004 g

There are three spheres. The largest and smallest were used by Professor J.H. Poynting and P.L. Gray in an ambitious experiment to investigate whether the gravitational attraction between anisotropic materials depended on their relative orientation. The small sphere was suspended on a torsion fibre and the largest sphere was placed close beside it with the crystal axes horizontal. The large sphere was rotated slowly about a vertical axis and they looked for a torque on the small sphere with the periodicity of this rotation but found no effect. On present understanding no effect would be expected.

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