CERTAIN HARMONIES OF THE SOLAR SYSTEM. 69 



It will be observed that when the planes of the orbits most nearly coincide with 

 the invariable plane, they yet make an angle of nearly 5° with the plane of the 

 sun's equator, except in the instance of Mercury, in which the inclination is scarcely 

 1°; while the Earth and Venus, under the variety of circumstances here indicated, 

 still, as it were, assert their character as half-planets, by preserving among them- 

 selves always nearly the same inclination/ 



In view of our hypothesis all along kept in view, the question would here seem 

 to be a pertinent one — Why so great an average deviation in the planes of the 

 planetary orbits from the plane of the sun's equator? 



The answer to this may, perhaps, be found in what has heretofore been insisted 

 on; viz. the acquisition of material in the nebulous state from extra-equatorial 

 portions of the sun's atmosphere ; it being added withal that such an acquisition 

 would not take place from both the northern and southern half-spheroids at tlie 

 same time.'^ 



The extra-equatorial acquisition, (37), of more dense material being thus mainly 

 from one side, that has, it would seem, tended to produce an average deviation in 

 thf! plane of the resulting orbit.^* In that aspect of the matter, and, in view also 

 of the Ancient State contemplated in (44) and in Table (F), it may not be 

 entirely without significance that the color of Neptune is a pure Avhite, while that 

 of Uranus is inclined to yellow, and that of Saturn, the other component [as in 

 Table (F)] is decidedly so. But Jupiter is, again, white, while Mars is ruddy, and 

 the Asteroids are — Juno of a pale yellow color, and the others reddish.* 



Then, again alternately, the half-planet Venus, and also our satellite are both 

 white ; while Mercury is nearly of a rose color.' In the case here supposed, it is 



' With M. Sporer's value of the iucliuation of the sun's equator, the numbers in column 2cZ will 

 be diminished 18'. 



^ An examination of Mr. Trowbridge's paper, already referred to \_Notes to (38) and (57) 

 respectively], shows that he has wrought with the same idea in view; though he has applied it to 

 the change in the solar axis of rotation. 



5 Unless, with Mr. Trowbridge, we say that " the invariable plane of the solar system must" 

 (also) " be the invariable plane" for " the primitive solar spheroid, and that it must have coincided 

 approximately with the plane of the sun's equator;" and so he compares the inclination of "the 

 invariable plane" to the ecliptic with that of the orbit of Neptune, with which it nearly agrees. In 

 such a case, with the average existing inclination of the plane of the sun's equator to those of the 

 planetary orbits ; it would seem that the sun's equator has itself changed its position ; the vicissi- 

 tudes being similar to those, (68), which, according to M. Laplace, the earth in its forming state 

 seems to have undergone. 



But it should here be borne in mind that the invariable plane has its position ascertained by a 

 reference to the conditions of material as now accumulated into planets with well-determined orbits ; 

 and so the invariable plane thus conditioned may very possibly be not coincident with "the invari- 

 able plane of the primitive solar spheroid." 



* Le del, par Amedee Guillerain, 4ieme Edit. pp. 283 and 284. 



= Are the white planets, then, in part derived from the one half-spheroid, and the planets of an- 

 other color from the other? and is the half-spheroid, which furnished the white series, the northern 

 one?(?) 



For, as respects the existing state of comparative activity in the two hemispheres of the sun, as 

 indicated by the appearance of the solar spots, " a very material difference in their frequency and 

 magnitude subsists in its northern and southern hemisphere ; those on the northern preponderating 



