Earth's Rocks to Meteorites. 229 



fifty times the velocity of sound in the air, or of a cannon ball. 



3. It is a necessary consequence of these velocities that 

 the meteors move about the sun, and not about the earth, 

 as the controlling body. 



4. There are four comets related to four periodic star- 

 showers, that have occurred on the dates April 20th, August 

 10th, November 14th and November 2*7 th. The meteoroides 

 which have given us any of these star-showers constitute a 

 gi-oup, each individual of which moves in a path which is 

 like that of the corresponding comet. The bodies are, how- 

 ever, now too far from one another to influence appreciably 

 each other's motions. 



5. The ordinary shooting stars in their appearance and 

 phenomena, do not differ essentially from the individuals in 

 star-showers. 



6. The meteorites of different falls differ from one 

 another in their chemical composition, in their mineral 

 forms and in their tenacity. Yet through all these differ- 

 ences they have peculiar common properties which distin- 

 guish them entirely from all terrestrial rocks.. 



7. The most delicate researches have failed to detect 

 any trace of organic life in meteorites. 



8. These propositions have practically universal accept- 

 ance among scientific men. We go on to consider others 

 which have been received with hesitation, or in some cases 

 have been denied. 



With a very great degree of confidence we may believe 

 that shooting stars are solid bodies. As we see them they 

 are discrete bodies, separated even in prolific star-showers 

 by large distances one from another. We see them pene- 

 trate the air many miles, that is, many hundred times their 

 own diameters at the very least. They are sometimes seen 

 to break in two. They are sometimes seen to glance in the 

 air. There is good reason to believe that they glance 

 before they become visible. Now, these are not the pheno- 

 mena which may be reasonably expected from a mass of gas. 



A spherical mass of gas, at the earth's distance from the 

 sun, must exceed in density air at one-sixth millimetre 

 pressure, or else the sun will scatter it. Such a mass would 



