The present treatise dealing with the Principles of Mechanism and Mechanics of Machinery is the result of a number of years' experience in teaching the subjects and in practising engineering, and endeavors to deal with problems of fairly common occur rence. It is intended to cover the needs of the beginner in the study of the science of machinery, and also to take up a number of the advanced problems in mechanics. As the engineer uses the drafting board very freely in the solution of his problems, the author has devised graphical solu tions throughout, and only in a very few instances has he used formulae involving anything more than elementary trigonometry and algebra. The two or three cases involving the calculus may be omitted without detracting much from the usefulness of the book. The reader must remember that the book does not deal with machine design, and as the drawings have been made for the special purpose of illustrating the principles under discussion, the mechanical details have frequently been omitted, and in cer tain cases the proportions somewhat modified so as to make the constructions employed clearer.