320 THE COMING OF MAN 



marvelous spectacle in the sky. Sometimes the tail 

 is so long that it reaches one quarter of the way 

 across the heavens. 



These wonderful visitors to our skies move in 

 regular orbits of their own. They come toward the 

 sun from far away, turn around it, and then go off 

 to a distance so great that we cannot follow them 

 with the strongest telescope. 



People used to be very much frightened at the 

 sight of a comet. They did not understand its 

 appearance, and were alarmed by it just as they were 

 when the moon went between the sun and the earth 

 and cut off the sun's light from the earth, causing an 

 eclipse. These things frightened them because they 

 did not form a part of the regular changes in nature 

 that men had become accustomed to, and they did 

 not understand what caused them. Although we do 

 not know what the comets are or where they come 

 from, our searchers after truth have found that they 

 obey a law, as does everything else in the whole uni- 

 verse, and they have figured out the path that many 

 of these comets follow. 



For a longer time, however, men have known what 

 makes an eclipse. When there is a full moon it some- 

 times happens that the earth gets so exactly between 

 it and the sun that the shadow of the earth falls upon 

 it. There is always a great shadow cast by the earth, 

 but it is not often that there is anything for it to fall 

 upon. So, when the moon gets in its way the circular 

 shadow that the earth makes goes across the moon's 

 face. Sometimes it only seems to take out a bite, but 

 at other times it covers the moon's face entirely, and 



