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 202 KINEMATICS OF MACHINERY.

highest interest, and which, besides this, is indeed essentially of importance to the right comprehension of our work. This subject is the History of Machine Development. I can only enter into the matter here very briefly ; partly because, as I have said, it does not lie directly in our way, and partly because the materials existing for such a history are as yet too few to enable me to enter into details with any degree of certainty.

This history of a development must be distinguished from a history of the ordinary kind. The latter gives us in chronological order a series of individual phenomena, which may be retro- gressive as well as progressive. The former seeks only to find the steps by which some known position has been reached, it repeats itself anew with each nation's growing civilisation, it even reflects itself in the development of each single individual. The history of machinery, at least of certain special machines mills, apparatus for transport, and the steam-engine for instance has been already somewhat completely written, and more and more, fortunately, is being done in this direction. The history of machine deve- lopment, on the other hand, was not possible without a previous distinct acquaintance with the real nature of the machine itself, the subject, that is, which we have been investigating, and this must form the foundation of as yet unmade investigations. Re- flection from things known and existing may always, however, throw some light upon the past, it is by this means principally that I must attempt to work from the stand-point which we have now reached.

At the commencement of a study of machine development it is first of all necessary to know distinctly what it is that makes a machine complete or incomplete. It is only possible to judge of the completeness of a machine from the excellence of the work produced by it, if we are able to estimate separately what part of the result is due to the skill of the workman. Certain Indian fabrics, for instance, are of extraordinary excellence and delicacy, although they have been made in most defective looms ; throughout the whole manufacture of these it is the weaver's dexterity that plays the most important part. In no machine, however, can we absolutely do away with human action, if it be for no further purpose than to start and stop the process. It appears, therefore, that the most complete machine is the one fulfilling best its own share of the

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