678 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



Inter-planetary Spaces, and the Relative Orbital Velocities 

 OF the Primitive Rings and Planets. 



I agree with Laplace that the nebula was first divided into rings, 

 and that each planet was formed by the concentration of the mat- 

 ter of a single ring into a globular mass ; so that the intervals, 

 could they all be accurately known, would indicate the width of 

 the rings that once filled the same spaces. But I propose to give 

 a very different explanation from that of Laplace, of the manner 

 in which the rings were separated from the parent neBula and 

 from each other. My idea is that a nebuljj could not rotate in a 

 resisting medium without having a large proportion of its lighter 

 matter drawn into its centre. The great central mass, thus accu- 

 mulated, would necessarily assume the office and power of a pri- 

 mary planet, and compel all the nebulous matter in the neighbor- 

 hood to perform the offices of secondary bodies ; that is to say, the 

 matter near the sun would either rush into its bosom, or revolve 

 in concentric orbits around the centre. 



The mutual attraction of all the parts of the nebula would tend 

 to bind it together, in rigid connection with the central mass, like 

 the parts of a vast planet. This aggregating tendency would be 

 opposed by the tendency of the matter, at different distances from the 

 sun to move Avith different orbital velocities. The greater the 

 difference of any two portions of the nebulous matter in their dis- 

 tances from the sun, the greater must have been their tendencies 

 to a difference of orbital velocities. If tht cohesive or aggregating 

 tendency could have been sufficiently powerful, the whole nebula 

 would have remained in a single mass. If, on the contrary, the 

 tendency to differ in orbital motion could have been unopposed, 

 there would have been a division of the nebula into an almost infi- 

 nite number of concentric rings, each of which would have moved 

 with a greater velocity the nearer it was to the sun. These two 

 forces antagonized each other ; one tending to prevent the forma- 

 tion of any rings, and the other tending to the formation of a • 

 countless number of rings of extreme narrowness ; the necessary 

 result of the antagonism was a compromise. A limited numiier 

 of rings were formed, which were wider the farther removed they 

 were from the central primary. Let us illustrate this proposition. 

 If a row of bodies could be arranged so as to extend in a radial 

 line from the sun to the orbit of Neptune, the mutual attraction of 

 those bodies would tend to preserve the line unbroken ; but the 

 differences in their orbital velocities would not permit this. The 



