ON TH£ SOLAR SYSTEM. 503 



supposed to retain its figure, is by means of a revolution much more rapid 

 than the sun's rotation. Some persons have attributed the appearance to 

 the refraction of the earth's atmosphere only ; but if it arose from any such 

 cause as this, its direction could scarcely be oblique with respect to the 

 horizon, and it is highly improbable that it should always happen to coincide 

 with the plane of the sun's rotation. (Plate XXXI. Fig. 470.) 



The sun is accompanied in his progressive motion "among the fixed stars 

 by ten planetary bodies, of different magnitudes, revolving round him, from 

 west to east, in orbits approaching to circles, and visible to us by means of 

 the light which they receive from him. These are Mercury, Venus, the Earth, 

 Mars, Juno, Pallas, Ceres, Jupiter, Saturn, and the Georgian planet. It 

 is unnecessary to adduce at present any arguments to prove the actual 

 existence or direction of any of these motions; their complete agreement with 

 the visible phenomena of the heavens, and with the laws of gravitation, will 

 hereafter appear to afi^brd sufficient evidence of the accuracy of the received 

 theory of the arrangement of the solar system. The motion of the earth is 

 the most unanswerably proved by the apparent aberration of the fixed stars, 

 derived from the different directions of this motion at different times, and 

 corresponding precisely with the known velocity of light, deduced from 

 observations of a very different kind. That the planets receive their hghc 

 from the sun, is undeniably shown by the appearance of the discs of 

 many of them, when viewed through a telescope, those parts of their surfaces 

 only being luminous, on which the sun shines at the time of observation. 



These planets are neither all in one plane, nor does any one of them remain 

 precisely in the same plane at all times; but their deviations from their 

 respective planes are inconsiderable, and they are commonly represented by 

 supposing each planet to revolve in a plane passing through the sun, and 

 the situation of this plane to be liable to slight variations. There is, however, 

 a certain imaginary plane, determinable from the situations, the velocities, 

 and the masses of the planets, which, like the centre of inertia, never changes 

 its position on account of any mutual actions of the bodies of the system, 

 and this plane of inertia is called the fixed ecliptic. Its situation is nearly 

 half way between the orbits of Jupiter and of Saturn; and it is inclined in a 

 small angle only to the plane of the earth's orbit, which is called the earth's 

 ecliptic, or simply the ecliptic. 



