THE MINOR PLANETS.

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slow, and the amount of change to be produced so great, that,even if it be considered theoretically possible for them to havethus attained their present positions, an interval long beyondall reasonable belief, or almost beyond imagination, would havebeen necessary for the purpose.

In fact, the dilferences existing between the various orbitsare practically sufficient to forbid our supposing that any con-ceivable series of perturbations could have sufficed to generatethem. At the same time we must allow that it is quite im-possible, owing to the number of bodies involved, and theextreme complication of the problem, to work backwards, so asabsolutely to determine whether the necessary conditions couldever have existed. An attempt to do so approximately was,however, some time since made by Encke, in the case of a fewselected orbits, the result of which, so far as it went, tended tonegative the supposition.

"We may therefore say, that the orbits of the first four MinorPlanets undoubtedly supported, to some extent, the hypothesisthat their origin might have been due to the explosion of alarger orb. But the orbits of those which have since been dis-covered in such large numbers, and the great differences foundto exist between very many of them, have well nigh given theabove-mentioned theory its final death-blow.

"We have already stated our reasons for believing that theaggregate mass, or bulk, of the Minor Planets is, comparativelyspeaking, very small. This is, we think, another argumentagainst the hypothesis of Olbers . So far as we can judge, anyplanet, by the explosion of which they might have been formed,would have been of so insignificant a size as hardly to beworthy of comparison with the other members of the planetaryfamily; unless we imagine an explosion to have occurred soterrific as to have almost entirely dissipated it into dust, or intomillions of fragments far too small for our observation; or that,by some fearful catastrophe, the greater portion of it was con-verted into gas, so that it disappeared from view, as a nebula,or as a series of nebulae too faint to be seen. Nothing, however,with which we are acquainted in the physics of the Earth , orof which we see traces in the Moon , in any wise suggests the