210 WALKS AND TALKS. 



stones with velocities exceeding that of a cannon ball. Light 

 is disengaged, as when the cannon ball strikes the iron target ; 

 and thus the whole cometary train is lighted up. The nearer 

 it approaches the powerfully attractive bodies of our system, 

 the greater these disturbances become the intenser the lumi- 

 nosity the more extended and the more widened the train of 

 finer materials. But do not think this train of stones is the so- 

 called luminous "tail" of the comet. The tail always turns 

 away from the sun ; the dark train follows in the path of the 

 comet. The cause of the tail is yet a mystery. It may be a 

 smoke of luminous particles driven off by the intense heat of 

 the sun. 



The comets all have to make a journey around the sun. 

 Some of them remain in our system and subject themselves to 

 the laws of the planetary family; but others can not be in- 

 duced to stay ; they rush onward with such velocity that all 

 the power of the sun and planets is not sufficient to stop them. 

 They launch out from our remotest shore, on the limitless 

 ocean of space which stretches to the shores of other systems, 

 and stretches beyond, farther than imagination can picture. 

 But the comet which becomes domiciled in our system seems 

 gradually to undergo disintegration, and by and by its borders 

 are spread so far as to brush the atmosphere of some planet 

 when passing near it. Our atmosphere has been thus pierced 

 by the outlying constituents of certain cometary trains. 

 Sometimes countless thousands of them shoot through the air. 

 These missiles move with a velocity as high as twenty to forty 

 miles a second, and the friction and condensation resulting 

 develop sufficient heat to render the missile luminous. 



We call it a meteor. We had not contemplated the meteor 

 as a burning fragment of an old decayed comet. But some of 

 our most splendid meteoric displays have resulted from clouds of 

 meteoroidal bodies which have been quite certainly identified 

 with recognized comets. At certain regular intervals, on or 

 about the sixteenth of November, occurs a celebrated meteoric 

 shower which comes from a meteoroidal train or cloud that 

 has been identified with Tempel's comet the first one observed 



