22 EFFECTS OF A RESISTING MEDIUM. SECT. III. 



orbit is, no doubt, as stable as that of any other of the 

 large planets, as the inclination is very small, but he will 

 have periodical variations of very long duration from the reci- 

 procal attraction between him. and Uranus, one especially of 

 an enormous duration, similar to those of Jupiter and Saturn, 

 and, like them, depending on the time of his revolution round the 

 sun, being nearly twice as long as that of Saturn. Mr. Adams 

 has computed that Neptune produces a periodical perturbation 

 in the motion of Uranus, whose duration is about 6800 years. 



The equilibrium of the system, however, would be deranged 

 if the planets moved in a resisting medium (X. 78) sufficiently 

 dense to diminish their tangential velocity, for then both the 

 excentricities and the major axes of the orbits would vary with 

 the time, so that the stability of the system would be ultimately 

 destroyed. The existence of an ethereal medium is now proved ; 

 and, although it is so extremely rare that hitherto its effects on 

 the motions of the planets have been altogether insensible, there 

 can be no doubt that, in the immensity of time, it will modify 

 the forms of the planetary orbits, and may at last even cause the 

 destruction of our system, which in itself contains no principle 

 of decay, unless a rotatory motion from west to east has been 

 given to this medium by the bodies of the solar system, which 

 have all been revolving about the sun in that direction for un- 

 known ages. This rotation, which seems to be highly probable, 

 may even have been coeval with its creation. Such a vortex 

 would have no effect on bodies moving with it, but it would 

 influence the motions of those revolving in a contrary direction. 

 It is possible that the disturbances experienced by comets, which 

 have already revealed the existence of this medium, may also, in 

 time, disclose its rotatory motion. 



The form and position of the planetary orbits, and the motion 

 of the bodies in the same direction, together with the periodicity 

 of the terms in which the inequalities are expressed, assure us 

 that the variations of the system are confined within very 

 narrow limits, and that, although we do not know the extent of 

 the limits, nor the period of that grand cycle which probably 

 embraces millions of years, yet they never will exceed what is 

 requisite for the stability and harmony of the whole ; for the 

 preservation of which every circumstance is so beautifully and 

 wonderfully adapted. 



