PRELIMINARY. 

 CHAPTER I. 



INTRODUCTORY. 



1. MECHANICS is a Natural Science; its data are facts of 

 experience, its principles are generalisations from experience. 

 The possibility of Natural Science depends on a principle which 

 is itself derived from multitudes of particular experiences the 

 " Principle of the Uniformity of Nature." This principle may 

 be stated as follows Natural events take place in invariable 

 sequences. The object of Natural Science is the description of 

 the facts of nature in terms of the rules of invariable sequence 

 which natural events are observed to obey. These rules of sequence, 

 discovered by observation, suggest to our minds certain general 

 notions in terms of which it is possible to state the rules in 

 abstract forms. Such abstract formulas for the rules of sequence 

 which natural events obey we call the " Laws of Nature." When 

 any rule has been established by observation, and the corresponding 

 Law formulated, it becomes possible to predict a certain kind of 

 future events. 



The Science of Mechanics is occupied with a particular kind 

 of natural events, viz. with the motions of material bodies. Its 

 object is the description of these motions in terms of the rules 

 of invariable sequence which they obey. For this purpose 

 it is necessary to introduce and define a number of abstract 

 notions suggested by observations of the motions of actual 

 bodies. It is then possible to formulate laws according to which 

 such motions take place, and these laws are such that the 



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