THE AUTHOR'S THEORY or THE TIDES 169 



by falling in upon the sun or one of the planets. This 

 much, nevertheless, can be asserted without qualification, 

 namely, that those asteroids ivhose eccentricity of orbit 

 is strongly marked are of cometary origin. 



Comets have their little brothers called meteors. 

 This is only to be expected from the very nature of the 

 case. It would be extraordinary indeed if by the explo- 

 sion of a star only one fragment, or one congeries of 

 fragments, should reach us; rather should we expect a 

 long train of scattered debris, many millions of miles in 

 length, composed of congealed globules of all sorts of 

 miscellaneous sizes. Thus Comet I, of 1861, has been 

 identified with one stream of meteors, Biela's comet with 

 another, and so on. Not only this, but there is a great 

 deal of spectroscopic evidence that comets possess a 

 chemical constitution strikingly similar to that of me- 

 teorites, which latter, of course, are only meteors that 

 have managed to reach the earth. All of these objects, 

 issuing in a fused state from the shattered hulk of their 

 parent star, and consequently more or less finely divided, 

 cool quickly in the frigid realms of space, and so remain 

 until their projectile motion is suddenly arrested, or 

 they come near the fiery furnace of the sun. When 

 either of these events occurs, the meteor explodes because 

 of the sudden expansion of its freshly heated gases with- 

 in. The reason why only the larger meteors attain the 

 earth in safety is because the friction of our atmosphere 

 is insufficient, by reason of its shallowness and lack of 

 greater density, to do more than slightly fuse their out- 

 side, as actual cases have proven. Sizable meteors that 

 do explode are known as bolides. 



EEMARKABLE COMETS 



In order to appreciate the interpretive value of the 

 principles just elucidated, the reader should compare the 

 descriptions of past comets given in such books as Flam- 

 marion's Popular Astronomy. Take, for example, the 

 great comet of 1843, which passed its perihelion within 

 33,000 miles (less than 1-25 of the sun's diameter) of the 



