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And then he would discourse on the Poisson-Navier theory of isotropic solids, and the impossibility of the fixed relation which that theory imposed between the modulus of rigidity and the modulus of compression; and refer with approval to the series of examples of "perfectly uniform, homogeneous, isotropic solids," which Stokes had shown could be obtained by making jellies of different degrees of stiffness.

It follows that the density of the aether must exceed 10-18, and its elastic modulus must exceed 103, which is only about 10-8 of the modulus of rigidity of glass.