It may be noticed that all machines, except milling machines, which act in straight lines and produce plane surfaces have reciprocating movement; the class includes planing, slotting and shaping machines; these, with lathes, constitute nearly the whole equipment of an ordinary fitting shop.
FORE:The name of having been an apprentice to a famous firm may sometimes have an influence in enabling an engineer to form advantageous commercial connections, but generally an apprenticeship is of value only as it has furnished substantial knowledge and skill; for every one must sooner or later come down to the solid basis of their actual abilities and acquirements. The engineering interest is by far too practical to recognise a shadow instead of true substance, and there is but little chance of deception in a calling which deals mainly with facts, figures, and positive demonstration.
Plato knew perfectly well that although rhetoricians and men of the world might be silenced, they could not be converted nor even convinced by such arguments as these. So far from thinking it possible to reason men into virtue, he has observed of those who are slaves to their senses that you must improve them before you can teach them the truth.L And he234 felt that if the complete assimilation of the individual and the community was to become more than a mere logical formula, it must be effected by a radical reform in the training of the one and in the institutions of the other. Accordingly, he set himself to elaborate a scheme for the purpose, our knowledge of which is chiefly derived from his greatest work, the Republic. We have already made large use of the negative criticism scattered through that Dialogue; we have now to examine the positive teaching by which it was supplemented.Prout remarked that Charlton was better. Fortunately no great damage had been done. He was suffering from some loss of blood, but in a day or two the patient would be able to give evidence. There would be enough sensation for the papers tomorrow."So far you have made it quite plain," Leona murmured, "but I fail to see that all the rest was easy."The first principle to be pointed out in regard to belts, to distinguish them from shafts as a means of transmitting power, is that power is communicated by means of tensile instead of torsional strain, the power during transmission being represented in the difference of tension between the driving and the slack side of belts. In the case of shafts, their length, or the distance to which they may be extended in transmitting power, is limited by torsional resistance; and as belts are not liable to this condition, we may conclude that unless there are other difficulties to be contended with, belts are more suitable than shafts for transmitting power throughout long distances. Belts suffer resistance from the air and from friction in the bearings of supporting pulleys, which are necessary in long horizontal belts; with these exceptions they are capable of moving at a very high rate of speed, and transmitting power without appreciable loss.Without further words or conscious movements from the silent pilot they managed to get him unhooked from his belt and parachute harness, to lower him, precariously limp, into the rubber boat, which Larry held onto as Jeff, half supporting his inert co-pilot, propelled it to their own craft.II.