Plaster model to illustrate the torsion of a rectangular prism.
This is a mathematical plaster model made by C. Delagrave of Paris, France. From the 1860s they were used extensively as teaching aids. In Germany they were used to illustrate advanced mathematics, whereas the French made more use of engineering models. Plaster was a popular material and many models were made in it. This model shows the torsion on a rectangular prism and was used to teach mechanics at the Royal College of Science at South Kensington.