ONE:In planing and turning, the tools require no exact form; they can be roughly made, except the edge, and even this, in most cases, is shaped by the eye. Such tools are maintained at a trifling expense, and the destruction of an edge is a matter of no consequence. The form, temper, and strength can be continually adapted to the varying conditions of the work and the hardness of material. The line of division between planing and milling is fixed by two circumstancesthe hardness and uniformity of the material to be cut, and the importance of duplication. Brass, clean iron, soft steel, or any homogeneous metal not hard enough to cause risk to the tools, can be milled at less expense than planed, provided there is enough work of a uniform character to justify the expense of milling tools. Cutting the teeth of wheels is an example where milling is profitable, but not to the extent generally supposed. In the manufacture of small arms, sewing machines, clocks, and especially watches, where there is a constant and exact duplication of parts, milling is indispensable. Such manufactures are in some cases founded on milling operations, as will be pointed out in another chapter.This is not making the percipi of objects their esse. Again, in the eighth chapter he tells us that the soul is in a certain way (π??) all things, since all things are either sensible or cogitable; and then he proceeds to explain what is meant by372 in a certain way. Sense and knowledge are distributed over things in such wise that their possibility is the possibility, and their actuality the actuality, of the things. They must, then, be either the things themselves or their forms. But the things themselves they are surely not, for the stone is not in the soul, but its form. In the Metaphysics, Aristotle expresses himself to the same effect, but even more explicitly. Criticising the Protagorean doctrine, he reduces it to an absurdity by urging that if there were nothing but sensibles, then nothing at all could exist in the absence of animated beings, for without them there would be no sensation. He admits that in the case supposed there would be neither feelings nor felt objects, since these presuppose a sentient subject; but adds, that for the substances (τ? ?ποκε?μενα) which produce the feeling not to exist is impossible; for there is something else besides the feeling which must necessarily exist before it.268 And immediately afterwards he clinches the argument by observing that if appearances were the only truth, there would be no independent existences, and everything would be relative, since appearances exist only in relation to some one to whom they appear. Now we need hardly say that this universal relativity was precisely what Ferrier contended for.
