Online Collections at UoB - Objects
Go to the Advanced Search
<< Viewing Record 1001 of 1323 >>
View : Light Box | List View | Image List | Detailed

ID number:  BIRRC-P0202
Institution:  Research and Cultural Collections
Named collection:  Historic Physics Collection
Artist / Maker:  Large sphere: Messrs Storey, Balancing sphere: Messrs Heenan, Two small spheres: Messrs Whitworth
Title / Object name:  Poynting’s spheres for determination of the gravitational constant
Object type:  Physics apparatus
Place made:  Manchester and Birmingham
Date made:  Large sphere; pre 1879, Balancing Sphere; 1889
Materials:  Lead antimony alloy (specific gravity 10.4), small spheres originally gilded
Measurements:  Large sphere: mass 153.4 kg, diameter 30.5 cm Balancing sphere: 76.5 kg, diameter 24.3 cm Small spheres 21.6 kg, diameter 15.8 cm

In 1890 Professor J. H. Poynting performed an experiment to determine the gravitational constant G and hence the mean density of the Earth using a large beam balance to measure the attraction between these massive spheres. The two smaller spheres were suspended from the arms of the balance and the force of attraction of the large sphere on one of them was equivalent to a weight of about 0.3 mg. This large sphere was moved from being under one to being under the other and the middle sized sphere was used as a counterbalance. Poynting’s value for G was 6.6984 x 10^-8 cgs units, compared to the modern value of 6.672.

<< Viewing Record 1001 of 1323 >>