To some men the material world is always presenting itself in the form of a series of fascinating puzzles, to be solved as one might work out a game of chess. The astronomer is given certain figures, and from those he intends to derive certain laws; the scientist knows the properties of certain materials and from those he is to reach some new combination that will produce a new result. He is not an inventor as much as he is a detective; he picks up the clews to certain happenings and constructs a working theory to fit them. In mechanics this theory that he constructs usually takes the form of a machine. And this machine is not so much a new discovery as it is the practical working-out of certain carefully-selected laws of nature.
