2021-04-17 12:24:18

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ENGLISH "What?"Motion or power may be varied to almost any degree by the ratio between the pistons of pumps and the pistons which give off the power, the same general arrangement of machinery answering in all cases; whereas, with gearing the quantity of machinery has to be increased as the motive power and the applied power may vary in time and force. This as said recommends hydraulic apparatus where a great force is required at intervals, and it is in such cases that it was first employed, and is yet for the most part used.The expense of patterns should be divided among and charged to the machines for which the patterns are employed, but there can be no constant rules for assessing or dividing this cost. A pattern may be employed but once, or it may be used for years; it is continually liable to be superseded by changes and improvements that cannot be predicted beforehand; and in preparing patterns, the question continually arises of how much ought to be expended on thema matter that should be determined between the engineer and the pattern-maker, but is generally left to the pattern-maker alone, for the reason that but few mechanical engineers understand pattern-making so well as to dictate plans of construction.

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.97

(1.) Under what conditions is hydraulic apparatus a suitable means for transmitting power?(2.) To what class of operations is hydraulic apparatus mostly applied?(3.) Why is not water as suitable a medium as air or steam in transmitting power for general purposes?The action of steam-hammers may also be divided into what is termed elastic blows, and dead blows.I will not consume space to explain the converse of this system of inventing, nor attempt to describe how a chance schemer would proceed to hunt after mechanical expedients to accomplish the valve movement in the example given.

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6. To meet the conditions of rotation in the wheel, and to facilitate the escape of the water without dragging, after it has expended its force upon the vanes, the reversed curves of the turbine is the best-known arrangement.At the same time bells rang ... and guns roared.Strains caused by cutting action, in planing or other machines, fall within and are resisted by the framing; even when the tools are supported by one frame and the material by another, such frames have to be connected by means of foundations which become a constituent part of the framing in such cases.

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2. The connection between the hammer drop and valve cannot be positive, but must be broken during the descent of the drop.In the flowerbeds in front of the station many corpses had been buried, especially those of soldiers who had been killed in the fight near Louvain. The station itself was well guarded, but, thanks to my passport and resolute manner, I gained admission and was finally ushered into the presence of the man who is responsible for the destruction of Louvain, Von Manteuffel.

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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. CHAPTER I

Shrinkage, or the contraction of castings in cooling, is provided for by adding from one-tenth to one-eighth of an inch to each foot in the dimensions of patterns. This is a simple matter, and is accomplished by employing a shrink rule in laying down pattern-drawings [97] from the figured dimensions of the finished work; such rules are about one-hundredth part longer than the standard scale.A learner should, in fact, consider the application and operative conditions of gearing as one of the main parts of the subject, and the geometry or even the construction of wheels as subsidiary; in this way attention will be directed to that which is most difficult to learn, and a part for which facilities are frequently wanting. Gearing may be classed into five modificationsspur wheels, bevel wheels, tangent wheels, spiral wheels, and chain wheels; the last I include among gearing because the nature of their operation is analogous to tooth wheels, although at first thought chains seem to correspond more to belts than gearing. The motion imparted by chains meshing over the teeth of wheels is positive, and not frictional as with belts; the speed at which such chains may run, with other conditions, correspond to gearing.This change in engineering pursuits has also produced a change in the workmen almost as thorough as in manipulation. A man who deals with special knowledge only and feels that the secrets of his calling are not governed by systematic rules, by which others may qualify themselves without his assistance, is always more or less narrow-minded and ignorant. The nature of his relations to others makes him so; of this no better proof is wanted than to contrast the intelligence of workmen who are engaged in what may be termed exclusive callings with people whose pursuits are regulated by general rules and principles. A machinist of modern times, having outgrown this exclusive idea, has been raised thereby to a social position confessedly superior to that of most other mechanics, so that shop association once so dreaded by those who would otherwise have become mechanics, is no longer an obstacle.

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