OUTLINES OF NATURAL PHILOSOPHY. 



of parts which can be compared with one ano- 

 ther, 



47. Two events which are determined hy cir- 

 cumstances precisely the same, are conceived to 

 happen in equal portions of time. 



0. A stone will fall to the ground from a given height 

 in the same space of time to-day that it did yester- 

 day, or that it will do to-morrow, or at any future 

 period. It is not necessary that the stone should 

 be of the same weight, for, as has been already pro- 

 ved, the weight of the falling body does not affect 

 the time of its descent (6). It is on this proposi- 

 tion, generalized and applied to the vibrations of a 

 pendulum or a balance, that the going of a clock or 

 watch is taken for a measure of time. 



Thus it is on the principle of the sufficient reason 

 that time is divided into equal portions. 



b. The imperfections of mechanism require, however, 

 that our chronometers should be frequently checked 

 by a comparison with the motion of the heavenly 

 bodies ; but as the circumstances that may influ- 

 ence the duration of the events are not easily dis- 

 covered in the case of those bodies, it has requi- 

 red the highest improvements in science to derive 

 an exact measure of time from astronomical obser- 

 vation. 



48. Time considered as a quantity increasing or 

 flowing uniformly, without regard to the measure- 

 ment 



