PT. I. 



Astronomy and Geology compared. 33 



the Sun and Jupiter, viz. 567,122,000 miles; when 

 the Earth is directly between the Sun and Jupiter, 

 the distance is diminished by the distance of the 

 Earth from the Sun, viz. 384,262,000 miles, and 

 the distances vary within these limits, in proportion 

 to the position of the planets in their respective 

 orbits. Now at these immense distances, the moment 

 of the eclipse of the satellites is calculated to seconds 

 reduced to Greenwich time, and another means is 

 thus given of ascertaining the longitude. Thus we 

 find that the revolutions of the. satellites of Jupiter 

 round that planet are known to us with as much 

 accuracy as the revolutions of our Moon round the 

 Earth, and that they are equally regular . and 

 constant. 



A still more convincing proof of the uniformity 

 and regularity of the motions of the planets is to be 

 found in the periodical transits of Venus over the 

 Sun's disc. As Venus is 25,296,000 miles nearer to 

 the Sun than the Earth is, the orbit in which she 

 describes her revolution is contained entirely within 

 ours ; if, therefore, the orbits were in the same 

 plane, or, to use a more popular form of expression, 

 upon the same level, Venus would be continually 

 passing and repassing between the Sun and the 



D 



