CH. XXXI. METEOR-SHOWERS. 299 



determined by Adams, and also independently by Leverrier. 

 It had been shown by searching out all the past accounts of 

 November showers that in times gone by, the earth passed 

 through these meteors a little earlier in the year than she 

 does now, and this could not be accounted for by any 

 irregularity in the movement of the earth. It looked there- 

 fore as if the orbit of the November meteors must be slowly 

 shifting, just as the orbits of the planets do, within certain 

 limits. It was upon this shifting that Adams founded his 

 calculations, and he worked out the meteor path with great 

 accuracy, showing that those astronomers had been right 

 who thought it extended beyond Uranus. This time the 

 problem was solved by pure astronomical reasoning and not 

 by a happy guess. But perhaps the most remarkable part 

 of the story is that in 1866, long after Adams had deter- 

 mined the orbit, a new comet was seen which was found to 

 move exactly along the path of the November meteors, in the 

 same way that the comet of 181 2 agrees with those which 

 fall in August. 



Although these two meteor- showers are the most impor- 

 tant, they are by no means the only ones crossed by our earth. 

 Any clear night, if you watch carefully, you may see (according 

 to the astronomer Proctor) about six shooting-stars in one 

 hour; and Professor Newton, of America, has calculated that 

 7,500,000 meteors large enough to be seen without a telescope 

 pass through our atmosphere in one single day and night. 

 At least a hundred sets of meteors, or meteor-systems as they 

 are called, are known to astronomers, and each one of these 

 is composed of millions of bodies; and you must bear in 

 mind that these systems do not move round us, but round 

 the sun, so that it is only because we happen to cross their 

 path that we know anything of them. It would be idle to 



