7 2 THE POPULAR SCIENCE MONTHLY. 



be more or less precluded by the known velocities, the retrograde 

 motion so frequently characterizing meteors and meteoi'ites, or else by 

 the chemical conditions that, for instance, are involved in the passage 

 of the meteorite through the sun's chromosphere. Whether meteorites 

 move or do not move in circumsolar orbits is at present impossible to 

 say ; because, while with our incomplete knowledge we cannot to-day 

 attach the character of periodicity to any known class of meteorites, 

 we are not justified in founding any conclusion on a negative result 

 with so limited a foundation. 



But even if all or some of them may have been, on their encounter- 

 ing the earth, members temporarily or permanently of the solar system, 

 we may with considerable probability consider them as having origi- 

 nally entered our system from the interstellar spaces beyond it. Such 

 at least must be our conclusion if we are to admit the unity of the 

 whole class of phenomena of meteorites and falling stars. For, since 

 the orbits of the two best-known meteoric streams, those namely of 

 August and November, have been identified with the orbits of two 

 comets, and since in regard to one of these (that of November) Lever- 

 rier has shown, with great probability, that as a meteoric cloud it 

 entered and became a member of our system only some 1,700 years 

 ago in consequence of the attraction of Uranus, while the August 

 meteoric ring only differs in this respect from it, that it had at a much 

 more remote period found an elliptic orbit round the sun : we are con- 

 strained on the assumption with which we started to recognize also in 

 a meteorite a visitor from the regions of remote space. And so far as 

 it goes, the observation by Secchi that the November falling stars 

 exhibit the magnesium lines is in harmony with this view. 



It may, however, further be said that the tendency of scientific 

 conviction is in the direction of recognizing the collection toward and 

 concentration in definite centres, of the matter of the universe, as a 

 cosmical law, rather than the opposite supposition of such centres being 

 the sources whence matter is dispersed into space. In the meteorites 

 that fall on our earth (certainly in considerable numbers) we have to 

 acknowledge the evidence of a vast and perpetual movement of space, 

 about which we can only reason as part of a great feature in the 

 universe which we have every ground for not supposing to be confined 

 within the limits of the solar system. 



That this matter, whether intercepted or not by the planets and 

 the sun, should to an ever-increasing amount become entangled in the 

 web of solar and planetary attraction, and that the same operation 

 should be collecting round other stars and in distant systems such 

 moving " clouds " of star-dust as have been treated by Schiaparelli, 

 Leverrier, and other astronomers, or individual masses of wandering 

 stone or iron, is a necessary deduction from the view that we have 

 assumed regarding the tendency of cosmical matter to collect toward 

 centres. But in order to trace the previous stages of the history of 



