A HISTORY OF SCIENCE 



motionless as the place in the universe to which the 

 motion and position of all other stars is referred. 



"Then follows the outermost planet, Saturn, which 

 completes its revolution around the sun in thirty 

 years ; next comes Jupiter with a twelve years' revolu- 

 tion; then Mars, which completes its course in two 

 years. The fourth one in order is the yearly revolution 

 which includes the earth with the moon's orbit as an 

 epicycle. In the fifth place is Venus with a revolution 

 of nine months. The sixth place is taken by Mercury, 

 which completes its course in eighty days. In the 

 middle of all stands the sun, and who could wish to 

 place the lamp of this most beautiful temple in another 

 or better place. Thus, in fact, the sun, seated upon 

 the royal throne, controls the family of the stars which 

 circle around him. We find in their order a harmoni- 

 ous connection which cannot be found elsewhere. 

 Here the attentive observer can see why the waxing 

 and waning of Jupiter seems greater than with Saturn 

 and smaller than with Mars, and again greater with 

 Venus than with Mercury. Also, why Saturn, Jupiter, 

 and Mars are nearer to the earth when they rise in the 

 evening than when they disappear in the rays of the 

 sun. More prominently, however, is it seen in the case 

 of Mars, which when it appears in the heavens at night, 

 seems to equal Jupiter in size, but soon afterwards is 

 found among the stars of second magnitude. All of 

 this results from the same cause namely, from the 

 earth's motion. The fact that nothing of this is to be 

 seen in the case of the fixed stars is a proof of their 

 immeasurable distance, which makes even the orbit of 

 yearly motion or its counterpart invisible to us." : 



62 



