Page:An Enquiry Concerning the Principles of Natural Knowledge.djvu/37

 property of iron as such can be manifested at an instant. Instantaneously there is simply a distribution of electricity and Maxwell’s equations to express our expectations. But iron is not an expectation or even a recollection. It is a fact; and this fact, which is iron, is what happens during a period of time. Iron and a biological organism are on a level in requiring time for functioning. There is no such thing as iron at an instant; to be iron is a character of an event. Every physical constant respecting iron which appears in scientific tables is the register of such a character. What is ultimate in iron, according to the traditional theory, is instantaneous distributions of electricity; and this ultimateness is simply ascribed by reason of a metaphysical theory, and by no reason of observation.

5.5 In truth, when we have once admitted the hierarchy of macroscopic and microscopic equations, the traditional concept is lost. For it is the macroscopic equations which express the facts of immediate observation, and these equations essentially express the integral characters of events. But this hierarchy is necessitated by every concept of modern physics — the molecular theory of matter, the dynamical theory of heat, the wave theory of light, the electromagnetic theory of molecules, the electromagnetic theory of mass.

6. Maxwell’s Equations. 6.1 A discussion of Maxwell’s equations would constitute a treatise on electromagnetism. But they exemplify some general considerations on physical laws.

These equations (expressed for an axis-system α). involve for each point of space and each instant of time the vector quantities $$(F_\alpha, G_\alpha, H_\alpha)$$, $$(L_\alpha, M_\alpha, N_\alpha)$$ and