SOLAR SYSTEM. 151 



herself one of the planets, revolves in like man- 

 ner. Beyond Saturn, Uranus has been discovered 

 describing an orbit of the same kind ; and between 

 Mars and Jupiter, four smaller bodies perform 

 their revolutions in orbits somewhat less regular 

 than the rest. These planets are all nearly 

 globular, and all revolve upon their axes. Some 

 of them are accompanied by satellites, or atten- 

 dant bodies which revolve about them ; and 

 these bodies also have their orbits nearly circu- 

 lar, and nearly in the same plane as the others. 

 Saturn's ring is a solitary example, so far as we 

 know, of such an appendage to a planet. 



These circular motions of the planets round the 

 sun, and of the satellites round their primary 

 planets, are all kept going by the attraction of 

 the respective central bodies, which restrains the 

 corresponding revolving bodies from flying off. 

 It is perhaps not very easy to make this operation 

 clear to common apprehension. We cannot illus- 

 trate it by a comparison with any machine of 

 human contrivance and fabrication : in such 

 machines everything goes on by contact and 

 impulse : pressure, and force of all kinds, is 

 exercised and transferred from one part to ano- 

 ther, by means of a material connexion ; by rods, 

 ropes, fluids, gases. In the machinery of the 

 universe, there is, so far as we know r , no material 

 connexion between the parts which act on each 

 other. In the solar system no part touches or 



