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ENGLISH ²Ô¾®¿Õ°®Ò»ÏÄÏÂÔØAs a means for transmitting power, shafts afford the very important advantage that power can be easily taken off at any point throughout their length, by means of pulleys or gearing, also in forming a positive connection between the motive-power and machines, or between the different parts of machines. The capacity of shafts in resisting torsional strain is as  the cube of their diameter, and the amount of torsional deflection in shafts is as their length. The torsional capacity being based upon the diameter, often leads to the construction of what may be termed diminishing shafts, lines in which the diameter of the several sections are diminished as the distance from the driving power increases, and as the duty to be performed becomes less. This plan of arranging line shafting has been and is yet quite common, but certainly was never arrived at by careful observation. Almost every plan of construction has both advantages and disadvantages, and the best means of determining the excess of either, in any case, is to first arrive at all the conditions as near as possible, then form a "trial balance," putting the advantages on one side and the disadvantages on the other, and footing up the sums for comparison. Dealing with this matter of shafts of uniform diameter and shafts of varying diameter in this way, there may be found in favour of the latter plan a little saving of material and a slight reduction of friction as advantages. The saving of material relates only to first cost, because the expense of fitting is greater in constructing shafts when the diameters of the different pieces vary; the friction, considering that the same velocity throughout must be assumed, is scarcely worth estimating."The orders issued by Monsieur Collins remain valid.
By classifying these processes, it will be seen that there is in all but a few functions to be performed by machines, and that they all act upon a few general principles. Engineering tools employed in fitting are, for example, all directed to the process of cutting. Planing machines, lathes, drilling machines, and shaping machines are all cutting machines, acting upon the same general planthat of a cleaving wedge propelled in straight or curved lines.
An apprentice in entering the workshop should avoid everything tending to an appearance of fastidiousness, either of manner or dress; nothing is more repulsive to workmen, and it may be added, nothing is more out of place in a machine shop than to divide one's time between the work and an attempt to keep clean. An effort to keep as neat as the nature of the work will admit is at all times right, but to dress in clothing not appropriate, or to allow a fear of grease to interfere with the performance of work, is sure to provoke derision."Yes, captain."The Germans had flung some more bridges across the river beyond Andenne, which had been used for the occupation of Namur chiefly, and lay idle now guarded by only one sentry. I left by the town-gate without any difficulties; the German soldiers jumped out of the way and stood to atten153tion, as soon as they noticed the Netherland flag flying at the front of the motor. To the right and the left of the gateway they had written in gigantic letters: "Newspapers, please!"
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Arrangement comes next; in this the first matter to be considered is convenience of manipulation. The cutting position should be so arranged as to admit of an easy inspection of the work. An operator having to keep his hand on the adjusting or feed mechanism, which is about twelve inches above the work, it follows that if the cutting level is four feet from the floor, and the feed handle five feet from the floor, the arrangement will be convenient for a standing position. As the work requires continual inspection and hand adjustments, it will for this reason be a proper arrangement to overhang both the supports for the rack and the cutting tools, placing them, as we may say, outside the machine, to secure convenience of access and to allow of inspection.  The position of the cutting bar, crank, connections, gearing, pulleys, and shafts, will assume their respective places from obvious conditions, mainly from the position of the operator and the work.I saw some extremely poor people, very old and stiff, to whom walking was nearly impossible. A Bavarian soldier escorted them. He had his rifle slung across his back and in both hands carried the luggage of the unfortunate creatures. He seemed to have come a long way already, for he looked tired, and the perspiration ran down his face. Although it is only natural to assist one's fellow-creatures, this scene touched me, for hitherto I had seen the Germans commit rough, inhuman deeds only.
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.Pastor Claes, mentioned in the above proclamation, has done very much for the miserable Louvain population; they owe him especially much gratitude for an act of devotion with regard to the murdered victims.
It may be mentioned in regard to rack gearing for communicating movement to the carriages of planing machines or other purposes of a similar nature: the rack can be drawn to the wheel, and a lifting action avoided, by shortening the pitch of the rack, so that it will vary a little from the driving wheel. The rising or entering teeth in this case do not come in contact with those on the rack until they have attained a position normal to the line of the carriage movement.There is, however, a principle in hydraulic machinery that must be taken into account, in comparing it with positively geared mechanism, which often leads to loss of power that in many cases will overbalance any gain derived from the peculiar action of hydraulic apparatus. I allude to the loss of power incident to dealing with an inelastic medium, where the amount of force expended is constant, regardless of the resistance offered. A hydraulic crane, for instance, consumes power in proportion to its movements, and not as the amount of duty performed; it takes the same quantity of water to fill the cylinders of such cranes, whether the water exert much or little force in moving the pistons. The difference between employing elastic mediums like air and steam, and an inelastic medium like water, for transmitting force in performing irregular duty, has been already alluded to, and forms a very interesting study for a student in mechanics, leading, as it does, to the solution of many problems concerning the use and effect of power.
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The relation between invention and the engineering arts, and especially between invention and machines, will warrant a short review of the matter here; or even if this reason were wanting, there is a sufficient one in the fact that one of the first aims of an engineering apprentice is to invent something; and as the purpose here is, so far as the limits will permit, to say something upon each subject in which a beginner has an interest, invention must not be passed over.Bicycling was of course out of the question; I shouldered my bicycle and stepped across the glowing cinders, which singed my soles. One spot could still be recognised as a street corner. Three soldiers emerged there suddenly and aimed at me with their rifles.
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