THE MOTION OF THE EARTH. 



CHAPTER II. 



MOTION. 



Are the Physical Forces modes of Motion? Motion defined 

 Philosophical Views of Motion, and the Principles to which 

 it has been referred Motions of the Earth and of the Solar 

 System Visible Proofs of the Earth's Motion on its Axis 

 Influence of the proper Motions of the Earth on the Condi 

 tions of Matter Theory of the Conversion of Motion into 

 Heat, &c. The Physical Forces regarded as principles inde- 

 pendent of Motion, although the Cause and often apparently 

 the Effects of it. 



MANY of the most eminent thinkers of the present time 

 are disposed to regard all the active principles of nature 

 as " modes of motion," to look upon light, heat, elec- 

 tricity, and even vital force, as phenomena resulting from 

 "change of place " among the particles of matter; this 

 change, disturbance, or motion, being dependent upon 

 some undefined mover.* 



The habit of leaving purely inductive examination for 

 the delusive charms of hypothesis of viewing the 



* " Motion, therefore, is a change of rectilinear distance between 

 two points. Allowing the accuracy of this definition, it appears 

 that two points are necessary to constitute motion ; that in all 

 cases, when we are inquiring whether or no any body or point is 

 in motion, we must recur to some other point which we can com- 

 pare with it ; and that if a single atom existed alone in the universe, 

 it could neither be said to be in motion nor at rest. 



" The space which we call quiescent is in general the earth's 

 surface ; yet we well know, from astronomical considerations, that 

 every point of the earth's surface is perpetually in motion, and that 

 in very various directions : nor are any material objects accessible 

 to our senses which we can consider as absolutely motionless, or 



