ZONE OF PLANETS BETWEEN MARS AND JUPITER. 93 



The orbits of Hygeia and Themis, being the largest of 

 all the orbits, completely inclose nearly all of them, and 

 lock into but a small number ; while the orbits of Mas- 

 silia, Astraea, Pallas, etc., lock into nearly all of the 

 orbits ; so that if we take hold of the orbit of Hygeia 

 (supposed to be a material hoop), it will support the 

 orbits of Iris, Thalia, Calliope, and two or three others, 

 while these in turn lock into and support all the rest. 

 Indeed, if we seize hold of any orbit at random, it will 

 drag all the other orbits along with it. This feature of 

 itself sufficiently distinguishes the asteroid orbits from all 

 the other orbits of the solar system. 



If we reject the theory that these asteroids were 

 originally united in one solid body, it seems nevertheless 

 difficult to avoid the conclusion that similar causes have 

 operated in determining the orbits of this zone of planets. 

 It is impossible to assign any cause for these resem- 

 blances without adopting some theory respecting the origin 

 of the solar system. The theory of gradual condensa- 

 tion, as developed by Laplace in the nebular hypothesis, 

 affords at least a plausible explanation of these phe- 

 nomena. 



Laplace supposed that the matter composing the bodies 

 of our solar system originally existed in the condition of 

 an immense nebula, extending beyond the limits of the 

 most distant planet that this nebulous mass had an ex- 

 ceedingly elevated temperature, and a slow rotation on 

 its axis that the nebula gradually cooled ; and as it con- 

 tracted in dimensions, its velocity of rotation, according 



