Reciprocating tools are divided into those wherein the cutting movement is given to the tools, as in shaping and slotting machines, and machines wherein the cutting movement is given to the material to be planed, as in a common planing machine. Very strangely we find in general practice that machine tools for both the heaviest and the lightest class of work, such as shaping, and butting, operate upon the first principle, while pieces of a medium size are generally planed by being moved in contact with stationary tools.
ONE:Whether there exist any realities beyond what are revealed to us by this evidence, and what sensible evidence itself may be worth, were problems already actively canvassed in Aristotles time. His Metaphysics at once takes us into the thick of the debate. The first question of that age was, What are the causes and principles of things? On one side stood the materialiststhe old Ionian physicists and their living representatives. They said that all things came from water or air or fire, or from a mixture of the four elements, or from the interaction of opposites, such as wet and dry, hot and cold.332 Aristotle, following in the track of his master, Plato, blames them for ignoring the incorporeal substances, by which he does not mean what would now be understoodfeelings or states of consciousness, or even the spiritual substratum of consciousnessbut rather the general qualities or assemblages of qualities which remain constant amid the fluctuations of sensible phenomena; considered, let us observe, not as subjective thoughts, but as objective realities. Another deficiency in the older physical theories is that they either ignore the efficient cause of motion altogether (like Thales), or assign causes not adequate to the purpose (like Empedocles); or when they hit on the true cause do not make the right use of it (like Anaxagoras). Lastly, they have omitted to study the final cause of a thingthe good for which it exists.
TWO:A policeman, standing rigidly outside the house, making signs with his hands to somebody. A sound of feet creeping down the area steps, the sudden pop and bang of a door forced in by a lever.The feed adjustment of the tool being intermittent and the amount of cutting continually varying, this movement should be performed by hand, so as to be controlled at will by the sense of feeling. The same rule applies to the adjustment of the rack for spacing; being intermittent and irregular as to time, this movement should also be performed by hand. The speed of the cutting movement is known from ordinary practice to be from sixteen feet to twenty feet a minute, and a belt two and a half inches wide must move two hundred feet a minute to propel an ordinary metal cutting tool, so that the crank movement or cutter movement must be increased by gearing until a proper speed of the belt is reached; from this the speed of intermediate movers will be found.
TWO:Nothing animate or inanimate in nature is uniform; plants, trees, animals, are all different; even the air we breathe and the temperature around us is constantly changing; only one thing is constant, that is time, and to this must we go for all our standards.
TWO:Still more important was the antithesis between Nature and convention, which, so far as we know, originated exclusively with Hippias. We have already observed that universality and necessity were, with the Greeks, standing marks of naturalness. The customs of different countries were, on the other hand, distinguished by extreme variety, amounting sometimes to diametrical opposition. Herodotus was fond of calling attention to such contrasts; only, he drew from them the conclusion that law, to be so arbitrary, must needs possess supreme and sacred authority. According to the more plausible interpretation of Hippias, the variety, and at least in Greek democracies, the changeability of law proved that it was neither sacred nor binding. He also looked on artificial social institutions as the sole cause of division and discord among mankind. Here we already see the dawn of a cosmopolitanism afterwards preached by Cynic and82 Stoic philosophers. Furthermore, to discover the natural rule of right, he compared the laws of different nations, and selected those which were held by all in common as the basis of an ethical system.63 Now, this is precisely what was done by the Roman jurists long afterwards under the inspiration of Stoical teaching. We have it on the high authority of Sir Henry Maine that they identified the Jus Gentium, that is, the laws supposed to be observed by all nations alike, with the Jus Naturale, that is, the code by which men were governed in their primitive condition of innocence. It was by a gradual application of this ideal standard that the numerous inequalities between different classes of persons, enforced by ancient Roman law, were removed, and that contract was substituted for status. Above all, the abolition of slavery was, if not directly caused, at any rate powerfully aided, by the belief that it was against Nature. At the beginning of the fourteenth century we find Louis Hutin, King of France, assigning as a reason for the enfranchisement of his serfs, that, according to natural law, everybody ought to be born free, and although Sir H. Maine holds this to have been a mistaken interpretation of the juridical axiom omnes homines natura aequales sunt, which means not an ideal to be attained, but a primitive condition from which we have departed: nevertheless it very faithfully reproduces the theory of those Greek philosophers from whom the idea of a natural law was derived. That, in Aristotles time at least, a party existed who were opposed to slavery on theoretical grounds of right is perfectly evident from the language of the Politics. Some persons, says Aristotle, think that slave-holding is against nature, for that one man is a slave and another free by law, while by nature there is no difference between them, for which reason it is unjust as being the result of force.64 And he proceeds to prove the contrary at length. The same doctrine of natural equality led to important political consequences, having, again according to Sir83 H. Maine, contributed both to the American Declaration of Independence and to the French Revolution.
