CERTAIN HARMONIES OF THE SOLAR SYSTEM. 21 



is concerned, the centrifugal force at the extremity of the radius of rotation, would 

 be as the density, and the attractive force, still acting at the same angle with the 

 plane of the parallel, be also as the density, so that the element of density being, 

 in eftect, all but excluded from the comparison, there would remain very nearly the 

 same ratio of the forces as before; so that the not yet " abandoned" portion of the 

 atmosphere would scarcely have its exterior spheroidal form affected.^ 



And, although the case is not just the same, divisions into something like sphe- 

 roidal shells resembling those here supposed may be^ 

 traced in the representations of the heads of comets, 

 among others that of 1680, as represented in Plate 

 VI. of the third volume of Delambre's Astronomie 

 Theorique et Pratique ; the same being copied from 

 the Histoire Celeste of Lemonnier. The appearance 

 in question is yet more conspicuous in the represen- 

 tations of the head of the great comet of 1858, given 

 by Prof. G. P. Bond, in Vol. III. of the Anwds of 

 the Observatory of Harvard College. A very faithful 

 copy of one of these is here given. 



(38) Now, the partially condensed shell thus 



formed (if indeed admissible) must itself have exerted a conservative power in pre- 

 venting the too frequent occurrence of cases like that of the asteroids; viz., by an 

 earlier holding together of the greater number of the "abandoned" equatorial por- 

 tions of the atmosphere in the process tending to form rings or planets.^ 



Nay, it might even be questioned whether the more dense portions of the atmos- 

 phere, earlier separated, may not in their progress toward tlie equatorial plane, 

 described in (25), have arrived at the state of equilibrium of the forces, before the 

 equatorial portions were ready for the same ; and so, the formation of a planet have 

 gone on thus far, from a shell instead of a ring. 



Just one change more, to be followed by its consequences, might then have taken 

 place. The more dense portions, being the first about to be " abandoned," might 

 be found to be further o^dward than the rarer equatorial portions ; and attaching 

 the latter to themselves by the attraction due to a greater density. 



(39) Now, the special arrangements of the two half-planets, Earth and Venus, are 

 as though what has here been discussed and explained, were entirely applicable to them. 



' Though the ellipticity of tlie same might be appreciably changed. 



= Which may indeed, in part, be consequent on the changes adverted to in Note 2, on p. 20. 



3 The oblate form of the spheroid here alluded to ; the more profuse radiation of heat due to a 

 greater condensation of the nebulous material in the polar region ; and the division of the envelope 

 into shells v^ere all insisted upon by the author of this paper in a communication made by him to 

 the American Association for the Advancement of Science, at their meeting in Montreal, in 185T. 

 The idea of a more profuse radiation of heat from the polar regions seems, since that date, to have 

 independently occurred to others; and a profound and thorough investigation of the form of the 

 oblate solar spheroid and its variations, as also of the density of the solar atmosphere, at the 

 various planetary distances, the relative breadth of the rings, etc., though without reference in that 

 connexion to a more profuse polar radiation, is given by David Trowbridge, A.M., in vol. xxxviii. 

 (Second Series) of the American Journal of Science and the Aria, Nov. 1864. 



