ONE:The loss of effect by the inertia of the pieces acted upon increases with the weight of the work; not only the loss of power, but also the expense of heating increases with the size of the pieces. There is, however, such a difference in the mechanical conditions between light and heavy forging that for any but a heavy class of work there would be more lost than gained in attempting to operate on both sides of pieces at the same time.The truths here touched on seem to have been dimly present to the mind of Plato. He never doubts that all knowledge must, in some way or other, be derived from experience; and, accordingly, he assumes that what cannot have been learned in this world was learned in another. But he does not (in the Meno at least) suppose that the process ever had a beginning. It would seem that he is trying to express in figurative language the distinction, lost almost as soon as found, between intelligence and the facts on which intelligence is exercised, An examination of the steps by which Meno��s slave is brought to perceive, without being directly told, the truth of the Pythagorean theorem, will show that his share in the demonstration is limited to the intuition of certain numerical equalities and inequalities. Now, to Plato, the perception of sameness and difference meant everything. He would have denied that the sensible world presented examples of these relations in their ideal absoluteness and purity. In tracing back their apprehension to the self-reflection of the soul, the consciousness of personal identity, he would not have transgressed the limits of a legitimate enquiry. But self-consciousness involved a possible abstraction from disturbing influences, which he interpreted as a real separation between mind and matter; and, to make it more complete, an inde213pendent pre-existence of the former. Nor was this all. Since knowledge is of likeness in difference, then the central truth of things, the reality underlying all appearance, must be an abiding identity recognised by the soul through her previous communion with it in a purer world. The inevitable tendency of two identities, one subjective and the other objective, was to coalesce in an absolute unity where all distinctions of time and space would have disappeared, carrying the whole mythical machinery along with them; and Plato��s logic is always hovering on the verge of such a consummation without being able fully to accept it. Still, the mystical tendency, which it was reserved for Plotinus to carry out in its entirety, is always present, though restrained by other motives, working for the ascertainment of uniformity in theory and for the enforcement of uniformity in practice.