INSTRUMENTS ILLUSTRATING 

 KINEMATICS, STATICS, AND DYNAMICS. 



Science of GEOMETRY teaches us about the sizes, the shapes, and 

 Motion, the distances of things ; to know sizes and distances we 

 have to measure lengths, and to know shapes we have to measure 

 angles. The science of Motion, which is the subject of the present 

 sketch, tells us about the changes in these sizes, shapes, and dis- 

 tances which take place from time to time. A body is said to 

 move when it changes its place or position ; that is to say, when 

 it changes its distance from surrounding objects. And when the 

 parts of a body move relatively to one another, i.e. when they 

 alter their distance from one another, the body changes in size, 

 or shape, or both. All these changes are considered in the science 

 of motion. 



Kinematics. It is divided into two parts ; the accurate description of 

 motion, and the investigation of the circumstances under which 

 particular motions take place. The description of motion may again 

 be divided into two parts, namely, that which tells us what changes 

 of position take place, and that which tells us when and how fast 

 they take place. We might, for example, describe the motion of 

 the hands of a clock, and say that they turn round on their axes 

 at the centre of the clock-face in such a way that the minute-hand 

 always moves twelve times as much as the hour-hand ; this is the 

 first part of the description of the motion. We might go on to 

 say that when the clock is going correctly this motion takes 

 place uniformly, so that the minute-hand goes round once in 



