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来源: 南方日报网络版     时间: 2020-01-28 16:12:42
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To obtain a true understanding of the nature of power is by no means the difficulty for a beginner that is generally supposed [12]; and when once reached, the truth will break upon the mind like a sudden discovery, and ever afterwards be associated with mechanism and motion whenever seen. The learner will afterwards find himself analysing the flow of water, the traffic in the streets, the movement of ships and trains; even the act of walking will become a manifestation of power, all clear and intelligible, without that air of mystery that is otherwise inseparable from the phenomena of motion. If the learner will go on farther, and study the connection between heat and force, the mechanical equivalent of heat when developed into force and motion, and the reconversion of power into heat, he will have commenced at the base of what must constitute a thorough knowledge of mechanics, without which he will have to continually proceed under difficulties.

This, again, reaches the proposition that power is heat, and heat is power, the two being convertible, and, according to modern science, indestructible; so that power, when used, must give off its mechanical equivalent of heat, or heat, when utilised, develop its equivalent in power. If the whole amount of heat represented in the fuel used by a steam-engine could be applied, the effect would be, as before stated, from ten to fifteen times as great as it is in actual practice, from which it must be inferred that a steam-engine is a very imperfect machine for utilising heat. This great loss arises from various causes, among which is that the heat cannot be directly nor fully communicated to the water. To store up and retain the water after it is expanded into steam, a strong vessel, called a boiler, is required, and all the heat that is imparted to the water has to pass through the plates of this boiler, which stand as a wall between the heat and its work.In forming an estimate of the value of his services, an apprentice sees what his hands have performed, compares it with what a skilled man will do, and estimates accordingly, assuming that his earnings are in proportion to what has been done; but this is a mistake, and a very different standard must be assumed to arrive at the true value of such unskilled labour.Inventions in machine improvement, no matter what their nature, must of course consist in and conform to certain fixed modes of operating, and no plan of urging the truth of a proposition is so common, even with a chance inventor, as to trace out the 'principles' which govern his discovery.The subject is an intricate one, and has been so much affected by the influence of machine improvement, and a corresponding decrease in what may be called special knowledge, that rules and propositions which would fifty years ago apply to the conditions of apprenticeship, will at the present day be wrong and unjust. Viewed in a commercial sense, as an exchange of considerations or values, apprenticeship can be regarded like other engagements; yet, what an apprentice gives as well as what he receives are alike too conditional and indefinite to be estimated by ordinary standards. An apprentice exchanges unskilled or inferior labour for technical knowledge, or for the privilege and means of acquiring such knowledge. The master is presumed to impart a kind of special knowledge, collected by him at great expense and pains, in return for the gain derived from the unskilled labour of the learner. This special knowledge given by the master may be imparted in a longer or shorter time; it may be thorough [20] and valuable, or not thorough, and almost useless. The privileges of a shop may be such as to offset a large amount of valuable labour on the part of the apprentice, or these privileges may be of such a character as to be of but little value, and teach inferior plans of performing work.


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