"The great question of the nature of ether," as Hertz justly calls it, includes the question of its relation to ponderable matter; for these two forms of matter are not only always in the closest external contact, but also in eternal, dynamic, reciprocal action. We may divide the most general phenomena of nature, which are distinguished by physics as natural forces or "functions of matter," into two groups; the first of them may be regarded mainly (though not exclusively) as a function of ether, and the second a function of ponderable matter--as in the following scheme which I take from my _Monism_: THE WORLD (NATURE, OR THE COSMOS) ---------------------------------+------------------------------------- ETHER--Imponderable. | MASS--Ponderable. ---------------------------------+------------------------------------- | 1. _Consistency_: | 1. _Consistency_: | Etheric (_i.e._, neither | Not etheric (but gaseous, fluid, gaseous nor fluid, nor solid). | or solid). | 2. _Structure_: | 2. _Structure_: | Not atomistic, not made up of | Atomistic, made up of infinitesimal, separate particles (atoms), but | distinct particles (atoms) continuous. | discontinuous. | 3. _Chief Functions_: | 3. _Chief Functions_: | Light, radiant heat, electricity,| Gravity, inertia, molecular heat, and magnetism. | and chemical affinity. ---------------------------------+------------------------------------- The two groups of functions of matter, which we have opposed in this table, may, to some extent, be regarded as the outcome of the first "division of labor" in the development of matter, the "primary ergonomy of matter." But this distinction must not be supposed to involve an absolute separation of the two antithetic groups; they always retain their connection, and are in constant reciprocal action. It is well known that the optical and electrical phenomena of ether are closely connected with mechanical and chemical changes in ponderable elements; the radiant heat of ether may be directly converted into the mechanical heat of the mass; gravitation is impossible unless the ether effects the mutual attraction of the separated atoms, because we cannot admit the idea of an _actio in distans_. In like manner, the conversion of one form of energy into another, as indicated in the law of the persistence of force, illustrates the constant reciprocity of the two chief types of substance, ether and mass.