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\begin{eqnarray} \left(\nabla^2-\frac{1}{\chi}\frac{\partial}{\partial t} \right) T(\mathbf{r}, t)&=&-\frac{1}{\kappa}H(\mathbf{r}, t),\\\\ \left(\nabla^2-\frac{1}{c^2}\frac{\partial^2}{\partial t^2}\right)p\left( \mathbf{r}, t \right)&=&-\rho\beta\frac{\partial^2}{\partial t^2}T\left(\mathbf{r}, t\right). \end{eqnarray}
These are the Phenomena of Springs and springy bodies, which as they have not hitherto been by any that I know
reduced to Rules, so have all the attempts for the explications of the reason of their power, and of springiness
in general, been very insufficient.
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