TIME AND PERIODICITY 15 



our measurements and whole science of Time depend 

 absolutely on the operation throughout Mature of 

 the Law of Periodicity, and (2) that the periodi- 

 cities which affect and determine animal and 

 vegetal life upon our Earth are the periodic move- 

 ments of rotation and revolution of that Earth 

 itself. 



Now it is to the curvilinear motions of the heavenly 

 bodies that we must ascribe our subjection to the 

 periodic law. If these heavenly bodies moved for 

 ever in straight lines, as they would do if unacted 

 on by natural forces, the periodic rhythm of Nature 

 would disappear. 



It is to the fact that all Nature is under the con- 

 straint due to the constant silent operation of 

 physical Force that we owe, therefore, the law which 

 determines the most essential features of vitality. 

 The pulsations in which life consists and by which 

 it is sustained are attributable to the constraint and 

 limitation which we recognise as the effect of the 

 operation of Natural Force. It is to this same cause 

 that we ascribe the resistance of cohering masses 

 in virtue of which sensation arises and by which our 

 experience is punctuated. It is by means of these 

 obstructions to free activity that our experience 

 is denoted, and by reference to these that it is 

 cognised. Indeed, Activity itself as we know it 



