"The theory of elasticity, and, in particular, the problem of the transmission of waves through an elastic medium now attracted the attention of... Cauchy and Poisson—the former a discriminating supporter, the latter a sceptical critic of Fresnel's ideas. In the future the developments of the theory of elasticity were to be closely associated with the question of the propagation of light, and these developments arose in great part from the labours of these two savants."