44 LIGHT SCIENCE FOR LEISURE HOURS. 



out to distances exceeding in some cases those at 

 which Uranus and Neptune pursue their wide careers. 

 We may conclude, then, of far the greater number of 

 the meteors the earth encounters, that their paths, 

 having their most distant portions so much farther 

 from the sun than our earth, must have their nearest 

 part to the sun much closer to the sun than the 

 earth is. So that if meteors were as large as planets, 

 it would necessarily happen that many meteors belong- 

 ing to systems which the earth encounters would be 

 seen, at certain seasons, shining close by the sun. 



But, as a matter of fact, meteors are individually 

 far too minute to be thus seen ; nor could all the 

 meteor systems traversed by the earth become visible 

 by the combined lustre of their components. 



It is clear, however, that the meteor systems tra- 

 versed by the earth can be but a few among the meteor 

 systems actually existing, and having paths carrying 

 their components nearer to the sun than the earth is. 

 Taking at random any such path, the chance that the 

 earth's path would cross it is indefinitely small ; so that 

 clearly an indefinite number of such systems must exist 

 in order that the earth might have a fair chance of 

 encountering a single one. And since she actually 

 encounters hundreds, it will be seen how enormous 

 must be the real number of systems actually existing. 



This mode of reasoning, though in strict accordance 

 with recognised and certain principles, may not seem 

 convincing at first sight. But, in reality, it will be 

 found that we quite commonly, and as it were uncon- 



