From all these examples of ancient machinery we see how force-closure has gradually made way for pair- or chain-closure. This process has first converted the complete force-closure into the force-closed pair of elements, by degrees these have been more and more closed until at last constrained pairs have been reached, and chains have unnoticed been built up from them. One thing, moreover, has helped another, each machine devised to aid hand-work furnishes the means of completing a part of some new and more extended machine. Thus,—as we have already seen,—simplicity or fewness of parts does not itself constitute excellence in a machine, but increased exactness in the motions obtained, with diminished demands on the intelligence of any source of energy,—and this even at the cost of a considerable multiplication of parts, or in the language we have employed, of links in the kinematic chaining.
Looking at the kinematic principle as a part of the higher unity of human development, we can recognise from all this that the first machinal arrangements were of a kind which we may designate as make-shifts. Certain constrainments of motion were required. Men obtained these as best they could, and by the necessity of the case,—for our investigation has shown that no other equally simple solutions were possible,—they used pairs of elements in their first incomplete form. Very gradually each invention came to be used for more purposes than those for which it was originally intended, and the standard by which its excellence and usefulness were judged was gradually raised. An external necessity thus demanded its improvement, and from this cause machinal ideas slowly crystallised themselves out, and gradually assumed forms so distinct that men could use them designedly in the solution of new problems. These attempts resulted in further improvements, and these in their turn led once more to new applications and more extended use.
We recognise here that wonderful tendency towards extension of the limits within which men can work which appears in such different degrees among different races, and which has therefore led to such unequal development among them. Some races possess this tendency in small measure;—their development makes but a few small steps in thousands of years;—they have remained more true to their original nature and submitted more readily to
