It was noted above that action by contact is not included, except by subsumption, in the mathematical formulations of technology or science. It should now be added that in all the concomitance and sequence with which the mathematical formulations of mechanical phenomena are occupied, the assumption of concomitance or sequence at a distance will fill the requirements of the formulæ quite as convincingly and commonly more simply than the assumption of concomitance by contact only. To realise the difficulties which beset this postulate of action by mechanical continuity solely, as well as the _prima facie_ imbecility of the principle itself, it is only necessary to call to mind the tortuous theories of gravitation designed to keep it intact, and the prodigy of incongruous intangibilities known as the ether,--a rigid and imponderable fluid. Associated with the principle of action by mechanical continuity alone is a second metaphysical postulate of science,--the conservation of energy, or persistence of quantity. Like its fellow it does not admit of empirical proof; yet it is likewise held to be of universal application. This principle, that the quantity of matter or of energy does not increase or diminish, or, perhaps better, that the quantity of mechanical fact at large is invariable, has a better presumptive claim to rank as a by-product of the machine technology; although such a claim could doubtless be allowed only with broad qualifications. Not that the principle was not known or not formally accepted prior to the machine age; long ago the Roman scholar and the scholastic philosophers after him declared _ex nihilo nihil, in nihilum nil posse reverti_. But throughout the era of handicraft there continued also to be devoutly held the postulate that the material universe had a beginning in an act of creation, as also that it would some day come to an end, a quantitative collapse. As the era of handicraft advanced and, apparently, as the discipline of life under that technology enforced the habitual acceptance of the proposition that the quantity of material fact is constant, much ingenuity and much ambiguous speech was spent in an endeavour to reconcile the mechanical efficiency of the creative fiat with the dictum, _ex nihilo nihil fit_. But down to the close of that era it remains true that, by and large, the peoples of Christendom continued to believe in the mechanically creative efficiency of the Great Artificer; although, it must be admitted, with an ever growing apprehension that in this tenet of the faith they were face to face with a divine mystery. The eighteenth-century scientists, and many even in the nineteenth century, continued to profess belief in a creative origin of material things, as well as also in a providential guidance of material events,--which latter must have been conceived to be exerted by some other means than action through mechanical contact, since one term of the relation was conceived not to be of a mechanical