158 LIGHT SCIENCE FOR LEISURE HOURS. 



systems, passing through the region of space lying 

 nearer to the sun than the sun's orbit. 



But even this is far from being all. We have 

 every reason to believe, in fact it may be said to have 

 been to all intents and purposes demonstrated, that 

 the wealth of meteoric distribution increases greatly 

 within the earth's orbit, increases much more rapidly 

 within the orbit of Venus, still more rapidly within the 

 orbit of Mercury, and most rapidly of all in the sun's 

 immediate neighbourhood. The proof of this has, of 

 course, not been derived directly from meteoric ob- 

 servation, for we can become directly conscious of no 

 meteor systems but those through which the earth 

 actually passes, nor even of these save by those occa- 

 sional transits through them during which a few thou- 

 sands of individual meteors are, as it were, swept out 

 of them, by the onward rushing earth. Yet by reason- 

 ing of obvious force, the existence of multitudinous 

 meteor systems, growing ever more numerous and ever 

 richer, towards the sun's neighbourhood, has been 

 clearly established. It has been found, first, that 

 meteor systems follow in the course of comets ; it has 

 next been shown that when the earth passes through 

 the track of a comet meteoric bodies in great numbers 

 are encountered ; it may be inferred then, first, that 

 every meteor system follows either a comet now 

 existing or one which, like Biela's, has been dissipated 

 by processes whose nature is not as yet known ; * and, 



1 It so happens that one of the most remarkable meteoric showers 

 ever seen the only one which was ever predicted before it had been 



