TWO:The sudden and varied resistance to line shafts tends to loosen couplings, destroy gearing, and produce sudden strains that are unknown in other cases; and shafting arranged with the usual proportions for transmitting power will soon fail if applied to driving trip-hammers. Rigid connections or metal attachments ace impracticable, and a slipping belt arranged so as to have the tension varied at will is the usual and almost the only successful means of transmitting power to hammers. The motion of trip-hammers is a curious problem; a head and die weighing, together with the irons for attaching them, one hundred pounds, will, with a helve eight feet long, strike from two to three hundred blows a minute. This speed exceeds anything that could be attained by a direct reciprocal motion given to the hammer-head by a crank, and far exceeds any rate of speed that would be assumed from theoretical inference. The hammer-helve being of wood, is elastic, and acts like a vibrating spring, its vibrations keeping in unison with the speed of the tripping points. The whole machine, in fact, must be constructed upon a principle of elasticity throughout, and in this regard stands as an exception to almost every other known machine. The framing for supporting the trunnions, which one without experience would suppose should be very rigid and solid, is found to answer best when composed of timber, and still better when this timber is laid up in a manner that allows the structure to spring and [107] yield. Starting at the dies, and following back through the details of a trip-hammer to the driving power, the apprentice may note how many parts contribute to this principle of elasticity: Firstthe wooden helve, both in front of and behind the trunnion; nextthe trunnion bar, which is usually a flat section mounted on pivot points; thirdthe elasticity of the framing called the 'husk,' and finally the frictional belt. This will convey an idea of the elasticity required in connecting the hammer-head with the driving power, a matter to be borne in mind, as it will be again referred to.To the unskilled, or to those who do not take a comprehensive view of an engineering business as a whole, the finishing and fitting department seems to constitute the whole of machine manufacturean impression which a learner should guard against, because nothing but a true understanding of the importance and relations of the different divisions of an establishment can enable them to be thoroughly or easily learned.
THREE:Grinding, no doubt, if traced to the principles that lie at the bottom, is nothing more than a cutting process, in which the edges employed are harder than any material that can be made into cutters, the edges firmly supported by being imbedded into a mass as the particles of sand are in grindstones, or the particles of emery in emery wheels.
THREE:But even the most perfect mastery of Greek would not284 have made Plotinus a successful writer. We are told that before taking up the pen he had thoroughly thought out his whole subject; but this is not the impression produced by a perusal of the Enneads. On the contrary, he seems to be thinking as he goes along, and to be continually beset by difficulties which he has not foreseen. The frequent and disorderly interruptions by which his lectures were at one time disturbed seem to have made their way into his solitary meditations, breaking or tangling the thread of systematic exposition at every turn. Irrelevant questions are constantly intruding themselves, to be met by equally irrelevant answers. The first mode of expressing an idea is frequently withdrawn, and another put in its place, which is, in most cases, the less intelligible of the two; while, as a general rule, when we want to know what a thing is, Plotinus informs us with indefatigable prolixity what it is not.
THREE:Moreover, the Platonic ideas were something more than figments of an imaginative dialectic. They were now beginning to appear in their true light, and as what Plato had always understood them to beno mere abstractions from experience, but spiritual forces by which sensuous reality was to be reconstituted and reformed. The Church herself seemed366 something more than a collection of individuals holding common convictions and obeying a common discipline; she was, like Platos own Republic, the visible embodiment of an archetype laid up in Heaven.533 And the Churchs teaching seemed also to assume the independent reality of abstract ideas. Does not the Trinity involve belief in a God distinct from any of the Divine Persons taken alone? Do not the Fall, the Incarnation, and the Atonement become more intelligible if we imagine an ideal humanity sinning with the first Adam and purified by becoming united with the second Adam? Such, at least, seems to have been the dimly conceived metaphysics of St. Paul, whatever may now be the official doctrine of Rome. It was, therefore, in order that, during the first half of the Middle Ages, from Charlemagne to the Crusades, Realism should have been the prevailing doctrine; the more so because Platos Timaeus, which was studied in the schools through that entire period, furnishes its readers with a complete theory of the universe; while only the formal side of Aristotles philosophy is represented by such of his logical treatises as were then known to western Christendom.
