236 SCIENCE FROM AN EASY CHAIR 



atmosphere. It is considered probable that comets 

 eventually break down into streams of meteors, and that 

 their "life" (if one may use that term) is, relatively to 

 that of other heavenly bodies (which -are all undergoing 

 change and, in many cases, decay), not a very long one. 

 But there are no facts at present known which enable us 

 to tell whether a given comet is young or old, and it would 

 have been a decided shock had it been found that Halley's 

 comet, which has so happily spent every seventy-sixth 

 year with us for so many centuries, had " burst up," or by 

 ' indisposition " had been unable to pay his usual visit as 

 expected in 1910. 



