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get over the difficulty (in which we should otherwise he in-volved) of supposing the orbital motion of the satellites tohave been originally reverse to that obtaining in the rest ofthe Solar System , and possibly reverse to that of the axialrotation of the planets themselves. We certainly hesitate tobelieve that any such reverse motion can have existed in theearly history of our System, not only upon the grounds ofsymmetry and analogy, but, if for no other reason, becauseit would involve in the greatest possible difficulties theimportant Nebular Theory of Laplace, which necessarilyassumes all the original motions to have been in one andthe same direction. It is, however, almost equally hard toconceive by what possible cause so vast a change in thesupposed direction of the axes of the planets, as we havesuggested, could have been brought about.*
So little is known about Uranus , that there is only one otherfact relating to it to which we wish to draw attention. Werefer to an interesting comparison between its light and that ofone of the satellites of Jupiter , which is to be found in Flam-marion’s “ Popular Astronomy ” (page 573). He mentions
* It must, however, be remembered, as we have already mentioned, thatwe have no positive proof as to the position of the plane of the equatorof Uranus , inasmuch as we cannot detect its axial rotation. It is onlyupon the ground of a probable analogy with Jupiter and Saturn that it issuggested, that the plane of its equator may nearly coincide with the orbitsof its satellites. If, however, this is not the case, we believe that it wouldmake a very great difference to observers upon Uranus , whether the axisof the planet may have a greater, or less, inclination than that of the orbitsof the satellites to the ecliptic, which is most probably about 82°. Thoseof our readers who are acquainted with mathematics may be able to seethat, if its inclination be less, and there be a precession of the equinoxesupon Uranus , then, during alternate halves of the period of that preces-sion, the apparent orbital motion of the satellites, as regards rotationfrom east to west, or vice versa , round the axis of Uranus would bereversed. A similar change would also occur during alternate halves ofthe period of the revolution of the nodes of the orbit of any one of thesatellites. We do not notice any such effects in our own Moon ’sapparent orbital path among the stars, because the inclination of theEarth ’s axis to the plane of the ecliptic, which is G6£°, is greater than theinclination of the plane of the Moon ’s path (which is in fact onlyabout 5°).