ONE:To exert a powerful force acting through but a short distance, percussive devices are much more effective and simple than those acting by maintained or direct pressure. A hammer-head may give a blow equal to many tons by its momentum, and absorb the reactive force which is equal to the blow; but if an equal force was to be exerted by screws, levers, or hydraulic apparatus, we can easily see that an abutment would be required to withstand the reactive force, and that such an abutment would require a strength perhaps beyond what ingenuity could devise.
TWO:Before I got there I passed the Halls of Louvain, the building that contained the world-famous library, with its numerous art-treasures. Only the outer walls were left standing, inside it was all ruins. All was reduced to dust, to miserable rubbish, and never will one single page be recovered of all those thousands of burned manuscripts.Shaping machines as machine tools occupy a middle place between planing and slotting machines; their movements correspond more to those of slotting machines, while the operation of the tools is the same as in planing. Some of the advantages of shaping over planing machines for certain kinds of work are, because of the greater facilities afforded for presenting and holding small pieces, or those of irregular shape; the supports or tables having both vertical and horizontal faces to which pieces may be fastened, and the convenience of the mechanism for adjusting and feeding tools.
ONE:Inherent or cooling strains in castings is much more intricate than shrinkage: it is, in fact, one of the most uncertain and obscure matters that pattern-makers and moulders have to contend with. Inherent strains may weaken castings, or cause them to break while cooling, or sometimes even after they are finished; and in many kinds of works such strains must be carefully guarded against, both in the preparation of designs and the arrangement of patterns, especially for wheels and pulleys with spokes, and for struts or braces with both ends fixed. The main difficulty resulting from cooling strains, however, is that of castings being warped and sprung; this difficulty is continually present in the foundry and machine-shop, and there is perhaps no problem in the whole range of mechanical manipulation of which there exists more diversity of opinion and practice than of means to prevent the springing of castings. This being the case, an apprentice can hardly hope for much information here. There is no doubt of springing and strains in castings being the result of constant causes that might be fully understood if it were not for the ever-changing conditions which exist in casting, both as to the form of pieces, the temperature and quality of metal, mode of cooling, and so on.He had been uneasy because he experienced no disagreeable consequences of that blow, and had therefore consulted the doctor at Bilsen, who thought that only his excited nerves had enabled him to withstand such a blow. Both had been locked up a couple of hours and their bicycles had been taken away, as also their papers. Mr. van Wersch, however, had an acquaintance at Bilsen with whom he and his companion found lodgings, and whither he was good enough to take me as well.
TWO:"It is a fine study in human nature," Lawrence replied. "All the evil emotions are here nicely chained up. I like to watch and study for myself. Let me sit down and smoke a cigarette and study."I sent the motor back to The Netherlands, and went with my companion to the commander's office, where we got a permit to go on by military train.
