This book is intended to present the elementary principles of mechanism in a way that will make it adapted for use in evening technical schools, trade schools, mechanic arts high schools, and other schools where it is desired to teach the subject thoroughly yet without going into the highly mathematical treatment. Typical problems are solved throughout the text and a large number of problems are included for solution by the student.

1. A Machine. A machine consists of a number of pieces or groups of pieces so arranged that, when a driving force is applied to the proper place, the various pieces operate together to do some useful work. Each of the pieces in a machine either moves or helps to guide some of the other pieces in their motion. A familiar example is the common sewing machine. Power is applied at the treadle, causing motion of the rod connected with the treadle; this motion is passed on up through the various parts with the final result that the cloth is stitched. It is evident that the machine consists of a frame and moving pieces; the frame supporting and guiding the moving pieces, while the moving pieces pass the forces along.

2. A Mechanism. A mechanism is one of the groups of pieces in a machine, all of which pieces are so connected that, when a definite motion is given to one of them, the others are caused to move in definite ways. The treadle, driving rod, crank shaft, and that part of the frame which supports them in the sewing machine, constitute a mechanism. A machine, therefore, consists of a series of mechanisms, each of which is doing its own work, and all of which work together to accomplish the purpose for which the machine is intended.

3. The Study of Mechanism. The study of mechanism is the study of the laws which govern the motions of the various parts of a machine and the forces which exist in or are transmitted by those parts. That branch of the subject which deals with the motions only, regardless of the forces, is often given the name Kinematics of Machines, while the part dealing with forces is called Dynamics of Machines,

In this book only the kinematics of machines and a few of the simpler problems relating to forces will be treated.

4. Importance of a Study of Mechanism. The importance of this study to one who has to do with machinery is very great. Whether he is engaged in using or in designing machinery he ought to know how to analyze the motions which the various pieces have and to determine the speeds of the pieces. He also ought to know how to design and connect the mechanisms in order to obtain a desired motion for any particular piece. Furthermore, he needs to be able to determine the forces which may be expected to exist in the several pieces when a known force is applied at a known point. In short, in order intelligently to design or handle a machine, a man should thoroughly understand the natural laws which enter into the operation of the machine, and the various methods which have been devised to apply those laws to the performance of definite work. It is to this end that the science of mechanism is devoted.

5. Design. - The design of a machine consists in adapting known mechanical appliances to meet special conditions. That is, there are certain elementary mechanical units such as levers, revolving wheels, screws, cams, cranks, connecting rods, sliders, etc., which form the basis of all mechanisms. The, designer must so proportion and arrange these as to accomplish the desired end. It is purposed in the present work to enumerate some of the more common of these units or elements and to consider each one separately, discussing the natural laws governing its design and operation. Some of the ways in which these units are combined into mechanisms will be studied, also the motions and forces in these mechanisms. Sometimes it is better to carry on such studies by means of graphical work on the drawing board and sometimes by calculation. Whichever method seems best in any particular case will be adopted in the present text, and very frequently both will be used as a check on each other.