Before attempting an answer, we shall state the scientific principle referred to, which is entitled to rank as one of the greatest of modern discoveries. All the forms of force are convertible amongst themselves. They are all ultimately identical, and are endlessly passing and repassing into each other: the mechanical, the chemical, the vital, are all one. 'The many' _are_ 'the one,' its varying phrases, its protean raiment. In short, there is but a single supreme force, ubiquitous and plastic, the fountain of all change. It now evolves itself in heat, now masks itself in light, reveals itself in electricity, or sleeps in the law of gravitation: one solitary pulse within Nature's vast machine, and behind the barrier of her laws. This force, thus endlessly changing, is neither diminished nor replenished; it is not added to, nor subtracted from; it is perennial, and is its own conservator. It is not synthesis, but analysis that has resolved it into unity. But can synthesis combine its manifold phases under one regulative notion? In realizing its general character we cannot discharge from our minds in turn all the known features of particular forces, so as to leave a vague resultant common to all, yet especially identified with none. The diverse types must have an _archetype_. What is that archetype? It seems to us self-evident that we must seek for it, not in nature, but in man; not in the lower plane of the cosmical forces, but in the human _will_, the root of our personality. Comte begins with the lowermost grade of force (to wit, the mechanical), and ascends with it, bringing all the finer and more subtle forms under its sway, and interpreting the higher by the lower. We, on the contrary, begin with the highest known type, that which lies nearest ourselves, with which we are earliest acquainted, and whence we derive our notion of force beyond ourselves; and we descend with it as a light to guide our footsteps amongst the lower. This we hold to be the correct, to be indeed the only admissible philosophical procedure. If it is only through the consciousness of force within ourselves that we have any intelligible notion of it in nature (and are thus first initiated into the idea), we must come back to the will for an explanation of what the one force external to us is. Our own personality supplies us with the archetype of which we are in search. We thus throw the plank across the chasm between man and nature; we interpret the latter by the former (not the reverse); and the discovery of the correlation of forces, and the conservation of energy, becomes the scientific equivalent of the doctrine of philosophical theology, that one supreme Will pervades the universe, that in nature lives and moves and has its being.