256 THE MAJOR PLANETS. 



there may be several in attendance upon it. From irregularities in its telesco- 

 pic appearance, some astronomers have supposed it to be surrounded by a ring 

 similar to Saturn's. Owing to the immense distance of this new world many 

 of its peculiarities must remain unknown to us. if is invisible to the naked . 

 eye, and has only a small diameter seen through the largest telescope, being * 

 equal in brightness to a star of the eighth magnitude. Four or five generations 

 of mankind pass away during the long period of its revolution, equal to nearly 

 165 of our years. The distance of Neptune being about thirty times greater 

 than that of the Earth from the Sun, it follows that the apparent diameter of 

 the Sun, seen from that remote world, is only ^ of the diameter seen by us, 

 or, as the Sun appears 30' wide to us, it must appear only 1' wide from Nep- 

 tune, and consequently the amount of light and heat must be about nine-hun- 

 dred times less than to us. Suppose the smaller of the two circles representing 

 the Sun on page 254 to be reduced one-third in diameter, which would make 

 it 2 ^ times less in area ; then its contrast with the larger circle will show the 

 comparative degree of light and heat at Neptune and the Earth. Its light is, 

 nevertheless, equal to that of more than three hundred and thirty full moons, 

 and the physical arrangements of the planet may be calculated to greatly 

 modify it. 



