It is a fundamental principle of dynamics that "force is wholly expended in the action it produces,"[291] therefore, if all the forms of energy in the universe are the result of pressure, that pressure must be _continuous_; if they are the result of impulses, these impulses must be _incessantly renewed_, and must recur with immeasurable rapidity. On either supposition, "the universe is not even temporarily automatic, but must be fed from moment to moment by an agency external to itself," and "the preservation of the universe is effected only by the unceasing expenditure of enormous quantities of work;"[292] that is, it is ceaselessly sustained by Divine Omnipotence--"He upholdeth all things by the word of his power." So much with respect to the first form of this hypothesis which regards atomic _attraction_ as the sole world-forming and world-conserving force. We turn now to that form of the hypothesis which considers atomic _repulsion_ as the grand primal force in which all the other physical forces, even gravitation itself, have their origin. This view is presented by Professor W. A. Norton, in his articles "On Cosmical and Molecular Physics" in the _American Journal of Science and Arts_. His theory rests essentially upon the following principles: 1. The doctrine of _inertia_ applied to all matter. 2. The existence of a single primary force of _repulsion_ exerted by every atom upon every other atom. 3. The existence of but one primary form of _elementary matter_, viz., the universal or luminiferous ether; the atoms, so called, of ordinary matter, and of the electric ether being but different masses of condensed luminiferous ether. 4. The doctrine of the _interception of force_ by matter. This is a necessary consequence of the fact that a certain portion of the propagated force is instantly expended in imparting motion to the molecules or atoms which it encounters, and is therefore abstracted from this force.