In fundamental opposition to the theory of vibration, or the kinetic theory of substance, we have the modern "theory of condensation," or the pyknotic theory of substance. It is most ably established in the suggestive work of J. C. Vogt on _The Nature of Electricity and Magnetism on the Basis of a Simplified Conception of Substance_ (1891). Vogt assumes the primitive force of the world, the universal _prodynamis_, to be, not the vibration or oscillation of particles in empty space, but the condensation of a simple primitive substance, which fills the infinity of space in an unbroken continuity. Its sole inherent mechanical form of activity consists in a tendency to condensation or contraction, which produces infinitesimal centres of condensation; these may change their degree of thickness, and, therefore, their volume, but are constant as such. These minute parts of the universal substance, the centres of condensation, which might be called _pyknatoms_, correspond in general to the ultimate separate atoms of the kinetic theory; they differ, however, very considerably in that they are credited with sensation and inclination (or will-movement of the simplest form), _with souls_, in a certain sense--in harmony with the old theory of Empedocles of the "love and hatred of the elements." Moreover, these "atoms with souls" do not float in empty space, but in the continuous, extremely attenuated intermediate substance, which represents the uncondensed portion of the primitive matter. By means of certain "constellations, centres of perturbation, or systems of deformation," great masses of centres of condensation quickly unite in immense proportions, and so obtain a preponderance over the surrounding masses. By that process the primitive substance, which in its original state of quiescence had the same mean consistency throughout, divides or differentiates into two kinds. The centres of disturbance, which _positively_ exceed the mean consistency in virtue of the _pyknosis_ or condensation, form the ponderable matter of bodies; the finer, intermediate substance, which occupies the space between them, and _negatively_ falls below the mean consistency, forms the ether, or imponderable matter. As a consequence of this division into mass and ether there ensues a ceaseless struggle between the two antagonistic elements, and this struggle is the source of all physical processes. The positive ponderable matter, the element with the feeling of like or desire, is continually striving to complete the process of condensation, and thus collecting an enormous amount of _potential_ energy; the negative, imponderable matter, on the other hand, offers a perpetual and equal resistance to the further increase of its strain and of the feeling of dislike connected therewith, and thus gathers the utmost amount of _actual_ energy.