TWO:It may in the abstract be claimed that the dignity of any pursuit is or should be as the amount of good it confers, and the influence it exerts for the improvement of mankind. The social rank of those engaged in the various avocations of life has, in different countries and in different ages, been defined by various standards. Physical strength and courage, hereditary privilege, and other things that once recommended men for preferment, have in most countries passed away or are regarded as matters of but little importance, and the whole civilised world have agreed upon one common standard, that knowledge and its proper use shall be the highest and most honourable attainment to which people may aspire.PREFACE
TWO:Machines and tools operating by percussive action, although they comprise a numerous class, and are applied in nearly all mechanical operations, have never received that amount of attention in text-books which the importance of the machines and their extensive use calls for. Such machines have not even been set off as a class and treated of separately, although the distinction is quite clear between machines with percussive action, and those with what may be termed direct action, both in the manner of operating and in the general plans of construction. There is, of course, no lack of formul? for determining the measure of force, and computing the dynamic effect of percussive machines acting against a measured or assumed resistance, and so on; but this is not what is meant. There are certain conditions in the operation of machines, such as the strains which fall upon supporting frames, the effect produced upon malleable material when struck or pressed, and more especially of conditions which may render percussive or positive acting machines applicable to certain purposes; but little explanation has been given which is of value to practical men.
TWO:69Our text-books, such as are available for apprentices, consist mainly of mathematical formul? relating to forces, the properties of material, examples of practice, and so on, but do not deal with the operation of machines nor with constructive manipulation, leaving out that most important part of a mechanical education, which consists in special as distinguished from general knowledge.
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