316 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1916. 



presented with a few changes by the Viennese astronomer Weiss. It 

 was thought that they could assume with some certainty that the 

 shooting stars are bodies as solid as are the meteorites which pene- 

 trate with cosmic velocity the atmosphere of the earth, where they 

 become glowing in the heated air and begin to shine, and after be- 

 ing resoh^ed to dust or consumed become extinct or pass out of the 

 atmosphere. 



After it had been shown that swarms of shooting stars have been 

 returning regularly for two and one-half thousand years and pro- 

 ceed from a definite point of radiation in the sky, then it was con- 

 sidered the only possibility that the swarms of meteors circling 

 around the sun intercept the orbit of the earth at some point, on 

 the approach to which, in consequence of the density of the earth, 

 a portion of them fall down upon our planet as little meteoric 

 bodies. From the period of rotation, direction, and other factors 

 we have learned how to calculate the course of the meteors and have 

 found that their orbits very nearly coincided with those of the 

 periodic comets. Thus the Leonids move in the orbits of the comet 

 Tempel, 1866, the Perseids in that of the comet 1862 III, and the 

 Bielids of the 27th to 29th of Novemlber in the course of the comet 

 Biela. The agreement is so consistently exact that a whole series 

 of meteor streams can with great probability be traced back to 

 orbits of known comets. That comets are divided by the influence 

 of the sun or of the planets, as has happened to the comet Biela, or 

 altogether break to pieces and scatter themselves along the course 

 of the comets and form a meteoric ring out of which come the 

 swarms or shooting stars ; all these coordinate occurrences tend very 

 convincingly to identif}^ the falling meteorites with the shooting 

 stars, and to the belief, therefore, that they are broken pieces 

 of comets. A difference between shooting stars and meteorites con- 

 sists, then, only in that the first named pass noiselessly across the 

 heavens and disappear, while the fireballs hurl their missiles, the 

 meteorites, with thundering noise upon the earth. This theory is 

 still ;held in esteem among astronomers, and is also taken up by 

 Trabert in his Textbook of Cosmic Physics, 1912. The hypothesis 

 can be quite briefly expressed in the following words : Comets which 

 have become periodic split up into periodic swarms of shooting stars 

 which revolve in the courses of the mother comet. The fireballs are, 

 then, nothing more nor less than shooting stars which have been 

 driven into lower layers of air and appear to us in larger sizes. 



According to all these conceptions one would expect that at times 

 of the abundance of shooting stars, especially of the Leonid and 

 Perseid swarms, there would occur an increase of meteorite falls. 

 Among the about 350 known falls some, to be sure, have fallen at 



