12 MOMENTUM OF THE PLANETS. 



CHAPTER II. 



MOMENTUM OF THE PLANETS A SOURCE OF NATURAL 



MOTIVE-POWER. ESTIMATES OF PLANETARY FORCES, 



MAGNITUDES, AND REVOLUTIONS. 



" Look downward on that Globe, whose hither side, 

 With light from hence, though but reflected, shines : 

 That place is earth, the seat of man." 



Milton's Paradise Lost. 



JV/TECHANICAL Philosophy, like the angel 

 described by Milton, lifts the student to 

 the central orb of the solar system, "the gate 

 of light," to take a preliminary view of the sub- 

 lime extent of the universe. 



To an observer of our planet, stationed on 

 the planet Venus, the reflection of sunshine ren- 

 ders the apparently dull surface of the earth as 

 brilliant as Venus appears to us in the evening 

 sky. The magnitude of our earth, great and 

 important as it appears to us, is only ~ part of 

 the magnitude of Jupiter, and less than ^ part 

 of the magnitude of the nearly invisible planet 

 Neptune, the existence of which was discovered 

 only a few years ago. 



So numerous are the stellar suns to other sys- 

 tems of worlds in infinite space, that the first 

 sight of their glorious splendor, revealed by a 



