80 GEOLOGY. 



accretion, the greater the progress toward circularity. This is qualified 

 somewhat by the perturbations which the planets create in one another's 

 orbits, and by the special conditions of aggregation, but remains essen- 

 tially true. For the large planets that have dominated their collecting 

 zones and presumably swept them thoroughly, the reductions of eccen- 

 tricity are subequal. For the very small bodies that presumably grew 

 but little, the eccentricities remain large, for the greater part. For 

 example, the eccentricity of Mercury, the smallest of the planets, 

 remains more than twice that of any other planet. Mars, the next 

 smallest in size, comes next in eccentricity among the planets, while 

 the asteroids, that probably grew but little, have high eccentricities as 

 a rule. Their orbits have doubtless been not a little disturbed by the 

 great influence of their powerful neighbor Jupiter, and a rigorous 

 application of so general a law as the one under consideration cannot be 

 made to the details of their orbits; but the tenor of the facts is very 

 suggestive. The highest eccentricity, .38, is as high as the highest eccen- 

 tricity assigned to the original nuclei of the planets. Of the 70 aster- 

 oids whose diameters are fairly well known, the half that are larger, 

 and presumably have grown most, have orbits less eccentric by 13.7 per 

 cent, than the half that are smaller, and presumably have grown less. 

 Of the orbital elements of 278 asteroids examined, the half having the 

 lowest inclination to the common plane of the system, and so best situ- 

 ated for accretion, have eccentricities 21.9 per cent, less than those of 

 greater inclination, The orbits of Neptune and Venus are exception- 

 ally circular, the former perhaps on account of its outermost position 

 and mode of accretion, as previously suggested, the latter for reasons 

 not obvious. Rigorously consistent results cannot be expected from 

 such antecedents as are postulated in a case of this kind. The degree 

 of\consistency noted is perhaps to be regarded as much more remarkable 

 than the departures from it. If this view of the spacing out of the 

 planets be entertained, a rational law may be substituted for the purely 

 numerical forimulatioii, : known .as Bode ? s law, viz., that the spacing 

 has been derived from a f airily consistent variation in the primitive 

 eccentricities of the planetesimals and nuclei of the parent nebula, in 

 which the outer were symmetrically greater than the inner. 



