ONE:In the last chapter we dealt at length with the theories of art, and especially of tragic poetry, propounded in Aristotles Poetics. For the sake of formal completeness, it may be mentioned here that those theories are adapted to the general scheme of his systematic philosophy. The plot or plan of a work answers to the formal or rational element in Nature, and this is why Aristotle so immensely over-estimates its importance. And, just as in his moral philosophy, the ethical element, represented by character-drawing, is strictly subordinated to it. The centre of equilibrium is, however, not supplied by virtue, but by exact imitation of Nature, so that the characters must not deviate very far from mediocrity in the direction either of heroism or of wickedness."Of course, of course," Leona murmured with her hand to her head. "My mind has not been quite so clear for the last few days. Go on."
ONE: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.
ONE:The lesser is the greaters enemy,
