"Poisson's] April, 1828... memoir is very remarkable... like Cauchy, [he] first obtains the equations of equilibrium in terms of stress-components, and then estimates the traction across any plane resulting from the "intermolecular" forces. The expressions... involve summations with respect to all the "molecules," situated within the region of "molecular" activity of a given one. Poisson... assumes... summations with respect to angular space about the given "molecule," but not... with respect to distance... The equations of equilibrium and motion of isotropic elastic solids... thus obtained are identical with Navier's."