THE SMITHSONIAN INSTITUTION. 143 



time for such a computation ; but, from what we already know, we 

 hazard little in venturing the opinion, that when this computation shall 

 be made, it will appear that, if the asteroid planets ever composed a 

 single body which exploded, as Olbers supposed, such explosion must 

 have occurred myriads of ijears ago. Indeed, the discovery of such a 

 host of asteroids seems to have stripped the theory of Olbers of nearly 

 all the plausibility it possessed when it was originally proposed; audit 

 would seem hardly less reasonable to suppose that the earth and Venus 

 originally constituted but one body, than to admit the same for the 

 thirty-three asteroids. 



But, if we reject thu theory of Olbers, what do we conclude"? That 

 the asteroids bear no special relationship to each other ? Do they not 

 all clearly indicate a family resemblance? And, if so, how do we ac- 

 count for this relationship ? 



There are several reasons for believing in some peculiar relationship 

 between the asteroids. 



1. Unlike the other planets of our system, they are all of diminutive 

 size — the largest of them hardly exceeding one or two hundred miles in 

 diameter. M. Leverrier, after a close examination of the nature and 

 amount of the influences exerted by the entire group of asteroids upon 

 the planets Mars and the earth, has arrived at the conclusion that the 

 sum total of the matter constituting the small planets between Mars and 

 Jupiter, including undiscovered as well as known asteroids, caimot ex- 

 ceed about one fourth of the mass of the earth. 



2. The asteroids, in their position, occupy a zone entirely distinct 

 from the other planets of the solar system. Between the orbits of Ju- 

 piter and Saturn, as well as between Saturn and Uranus, is an immense 

 interval, furnishing space enough for a host of little bodies to circulate 

 around the sun ; but in not a solitary instance has any such body been 

 found, except between Mars and Jupiter. Some may attempt to ac- 

 count for this circumstance, by saying that astronomers have long been 

 watching exclusively this portion of space, and have left all other re- 

 gions entirely unexplored. An exploration conducted upon such a prin- 

 ciple is simply a physical impossibility. If there were a small planet 

 between the earth and Mars, it would have stood the same chance of 

 detection, in the explorations of the past ten years, as if it were situated 

 between Mars and Jupiter ; and, indeed, it would have stood a better 

 chance of detection, inasmuch as it would appear of greater brightness 

 on account of its proximity to us. If there were a small planet circu- 

 lating between Jupiter and Saturn, it would have stood the same chance 

 of detection as if it had been placed this side of Jupiter, except that it 

 would appear somewhat fainter on account of its increased distance. 

 The fact that we have discovered thirty-three small planets between 

 Mars and Jupiter, and not a solitary one in any other portion of the 

 solar system, points to something special in this region of the heavens. 

 In other words, we have discovered a limited zone of little planetary 

 bodies, and have not been able to discover a single body of the same 

 class situated out of this zone. 



3. The orbits of these little bodies present some special peculiarities. 

 The ascending nodes of the orbits are not distributed uniformly 



through the zodiac. The ascending nodes of twenty-two orbits are 



