? 305] Comets and Meteors 395 



tinuous spectrum, and in a few cases first in 1881 the 

 spectrum has been distinct enough to shew the Fraunhofer 

 lines crossing it. But the continuous spectrum seems also 

 to be due in part .to solid or liquid matter in the comet itself, 

 which is hot enough to be self-luminous. 



305. The work of the last 30 or 40 years has established 

 a remarkable relation between comets and the minute bodies 

 which are seen in the form of meteors or shooting stars. 

 Only a few of the more important links in the chain of 

 evidence can, however, be mentioned. Showers of shooting 

 stars, the occurrence of which has been known from quite 

 early times, have been shewn to be due to the passage of 

 the earth through a swarm of bodies revolving in elliptic 

 orbits round the sun. The paths of four such swarms 

 were ascertained with some precision in 1866-67, and found 

 in each case to agree closely with the paths of known 

 comets. And since then a considerable number of other 

 cases of resemblance or identity between the paths of 

 meteor swarms and of comets have been detected. One 

 of the four comets just referred to, known as Biela's, with 

 a period of between six and seven years, was duly seen on 

 several successive returns, but in 1845-46 was observed 

 first to become somewhat distorted in shape, and afterwards 

 to have divided into two distinct comets ; at the next return 

 (1852) the pair were again seen; but since then nothing 

 has been seen of either portion. At the end of November in 

 each year the earth almost crosses the path of this comet, and 

 on two occasions (1872, and 1885) it did so nearly at the time 

 when the comet was due at the same spot ; if, as seemed 

 likely, the comet had gone to pieces since its last appearance, 

 there seemed a good chance of falling in with some of its 

 remains, and this expectation was fulfilled by the occurrence 

 on both occasions of a meteor shower much more brilliant 

 than that usually observed at the same date. 



Biela's comet is not the only comet which has shewn 

 signs of breaking up ; Brooks's comet of 1889, which is 

 probably identical with Lexell's (chapter XL, 248), was 

 found to be accompanied by three smaller companions ; 

 as this comet has more than once passed extremely close 

 to Jupiter, a plausible explanation of its breaking up is at 

 once given in the attractive force of the planet. Moreover 



