SECT, iv.] SATELLITES OF SATUEN AND TJEANUS. 37 



experience, that of Bacon is not the least remarkable. " It 

 produces in me," says the restorer of true philosophy, "a doubt 

 whether the face of the serene and starry heavens be seen 

 at the instant it really exists, or not till some time later : and 

 whether there be not, with respect to the heavenly bodies, a 

 true time and an apparent time, no less than a true place and 

 an apparent place, as astronomers say, on account of parallax. 

 For it seems incredible that the species or rays of the celes- 

 tial bodies can pass through the immense- interval between 

 them and us in an instant, or that they do not even require 

 some considerable portion of time." 



Great discoveries generally lead to a variety of conclusions ' 

 the aberration of light affords a direct proof of the motion of 

 the earth in its orbit ; and its rotation is proved by the theory 

 of falling bodies, since the centrifugal force it induces retards 

 the oscillations of the pendulum (N. 100) in going from the 

 pole to the equator. Thus a high degree of scientific know- 

 ledge has been requisite to dispel the errors of the senses. 



The little that is known of the theories of the satellites of 

 Saturn and Uranus is, in all respects, similar to that of 

 Jupiter. Saturn is accompanied by seven satellites, the most 

 distant of which is about the size of the planet Mars. Its 

 orbit has a sensible inclination to the plane of the ring ; but 

 the great compression of Saturn occasions the other satellites 

 to move nearly in the plane of his equator. So many circum- 

 stances must concur to render the two interior satellites vi- 

 sible, that they have very rarely been seen. They move exactly 

 at the edge of the ring, and their orbits never deviate from its 

 plane. In 1789, Sir William Herschel saw them like beads, 

 threading the slender line of light which the ring is reduced 

 to, when seen edgewise from the earth. And for a short 

 time he perceived them advancing off it at each end, when 

 turning round in their orbits. The eclipses of the exterior 

 satellites only take place when the ring is in this position. 

 Of the situation of the equator of Uranus we know nothing, 

 nor of his compression ; but the orbits of his satellites are 



