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DYNAMICS. 

 CHAPTER XL. 



MATTER AND FORCE. 



DYNAMICS is defined as the science which investi- 

 gates the action of force. The common term mechanics 

 is often applied to this science, erroneously, according 

 to the highest modern authorities, who restrict that 

 term to the " science of machines and the art of 

 making them." The ideas of force and matter are 

 inseparably associated together, force being recog- 

 nisable by its effects on material bodies. Dynamics 

 considers the action of forces on solid, liquid, and 

 gaseous bodies. Liquid and gaseous bodies have already 

 been considered, so far as seemed necessary for our 

 purpose. In this part of the work some of the 

 elementary dynamical facts and principles applied 

 to solid bodies will be noted. 



The measurement of foodies is accomplished 

 by means of standard bodies with which the body to 

 be measured is compared. 



The STANDARD OF LENGTH, by means of which 

 the linear extension of a body is estimated, is called 

 the yard in English measure (one yard = 3 feet 

 = 36 inches). It is an arbitrary measure enacted 

 by Parliament, and is the distance between the 

 centres of the transverse lines in the two gold 

 plugs in the bronze bar deposited at the office of 

 the Exchequer. The French standard of length is the 



