LAWS OF MOTION. 409 



Vine that either of these bodies are naturally 

 disposed to persevere in a state of rest, more 

 than solid matter can persevere in a state of 

 motion in a right line, unless compelled to 

 change that state by some external force. 

 These bodies are essentially active, and when 

 left to follow their natural power, are in per- 

 petual motion; so far from persevering at rest, 

 unless they are moved by a force impressed 

 upon them, they require a force to be impressed 

 on them, to prevent them from moving, the 

 power by which they are able to move, with a 

 Velocity so immense as they are found to do, is 

 not derived, but is inherent ; it does not pro- 

 ceed from external impulse, but from internal 

 energy ; not vi effecto, but causa motns ; not 

 from any active, or repulsive, power in the 

 bodies on which they fall, and from whence 

 they are reflected ; but owing to an innate qua- 

 lity which they derive from the source out of 

 which they emanate. 



However admissible the assertion might 

 be, that the motive power of the sun itself, 

 might impel the rays from its surface, with a 

 motion sufficient to traverse the whole of the 

 planetary spheres ; it is impossible to ascribe 

 the reflection from inert surfaces on which these 

 rays have fallen, to any power which those sur- 

 faces possess because a passive body can 

 never be the cause of action ; nor can motion 



