Page:The Kinematics of Machinery.djvu/78

 CHAPTER II.

PHORONOMIC PROPOSITIONS,

4. Preliminary Remarks.

THE science of Mechanism is a derived science, and has as we have already said its foundations in Applied Mechanics and Mathematics. It chooses from the first a special part, in consider- ing chiefly those motions which occur through latent forces, and are therefore conditioned by the geometric properties of the pieces transmitting these forces. Its problems therefore lie, for the most part, in a well defined portion of Mechanics the geometrical. This department does not always receive the same name in scientific books; it is best called Phoronomy. Frequently it is simply called Kinematics, but this seems to be a misunder- standing of the word. Ampere at least, who invented the name, did not intend it to be used in this sense. It is at the same time unnecessary so to employ it, for Phoronomy is quite sufficient, and is besides more distinctive than Kinematics. Phoronomy is, therefore, the study of the measurement of the motions of bodies of every kind, and has become specially the study of the geometric representation of motions. We therefore retain the designation Phoronomy, and as we shall frequently have to employ its propositions, especially so far as they concern rigid bodies, it will be well here to review a portion of them.