16 OUTLINES OF NATURAL PHILOSOPHY. 



perties of body. Whether a passage of some invi- 

 sible substance from the one body to the other it> 

 not to be inferred in such instances, will hereafter 

 be considered. 



b. As the action of bodies on one another generally 

 involves motion, the properties or laws of motion 

 constitute one of the main objects of natural phi- 

 losophy. The doctrine which treats of those pro- 

 perties is, however, modified by the constitution of 

 the bodies to which motion is communicated. 





38. When bodies are free to obey the impulses 

 communicated to them, the science which treats of 

 their motion is called DYNAMICS. 



a. Dynamics is the most elementary branch of the 

 doctrine of motion, and the most general in its 

 principles. The term signifies literally the doctrine 

 of power ; power or force being known to us only 

 as the cause of motion, and being measured by the 

 motion it produces. 



b. In Dynamics, we abstract entirely from the figure of 

 the body moved, and treat of it as if its matter were 

 all concentrated in a single point. 



39- When bodies, whether by external circum- 

 stances, or by their connection with one another, 

 are not left at liberty to obey the impulses given, 

 the principles of dynamics must receive a certain 

 modification before they can be applied to them. 



The 



