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TWO: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.In adding another to the large number of books which treat upon Mechanics, and especially of that class devoted to what is called Mechanical Engineering, it will be proper to explain some of the reasons for preparing the present work; and as these explanations will constitute a part of the work itself, and be directed to a subject of some interest to a learner, they are included in the Introduction.