674 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



When the nebulous wheel, from whence the solar sj^stem was 

 formed, commenced its rotation, it must have been composed of 

 matter which was exceedingly attenuated; quite as much so as 

 that of any comet, and, if possible, more so: it is, therefore, per- 

 fectly reasonable to presume that it was subjected to the influence 

 of the same resisting medium which now has such a decided eflect 

 upon Encke's comet. 



If, at the commencement of its rotation, the nebula was no more 

 dense or massive in the centre than elsewhere, the first effect of 

 the resisting medium would be to cause a large portion of the 

 lighter matter to accumulate there, and assume the office of a pri- 

 mary body — a sun. The attraction of this central mass would at 

 once establish orbital motions in all the surroundinsr nebulous 

 matter, whatever might be its form or condition. The laws of 

 Kepler, so called, that now govern the motions of all secondary 

 planets, must have controlled the motions of the secondary nebu- 

 lous matter, that was thus necessarily forced to move in orbits pr 

 rings around the central body. According to these laws, the por- 

 tions that were nearest to the centre, but not actually attached to 

 it, must have moved around it with the greatest velocity; and 

 those portions which were most remote, with the least velocity. 



Sir Charles Lyell, in his " Principles of Geology," objected to 

 the prevailing opinions concerning geological catastrophies; and 

 insisted that it was more philosophical to account for the changes 

 which the earth has undergone, by referring them to the operation 

 of still existing causes. I am not only a convert to his doctrine, 

 but I would apply it to the formation of the planets. The same 

 causes which now produce the differences of orbital velocities, were 

 in operation before the planets were formed, and caused diflTerences 

 in the velocities of the chaotic materials of which the planets were 

 subsequently composed. If all the planets could now be crumbled 

 to dust, and that dust be scattered equally between the orbit of 

 Neptune and that of Mercury, — each separate particle of the dust 

 would have a tendency to move in an orbit of its own. This ten- 

 dency would, in some degree, be overcome by the mutual attrac- 

 tion of the particles for each other; and the result would be the 

 formation of a series of concentric rings, differing in width and 

 velocities: the width of the rings would increase, and the veloci- 

 ties decrease, in accordance with their increasing distances from 

 the sun. In fact, the same law prevailed during the formation of 

 the planets as that which now determines their relative velocities. 



