

ASTRONOMY. 431 



much gravity to retain it in its orbit ; that is, it 

 must fall as far from B to 4, in the time that the 

 projectile force would carry it from B to c, other- 

 wise it would not describe the curve B D, as is 

 evident from the figure. But in as much time as 

 the planet moves from B to C, in the higher part 

 of its orbit, it moves from I to K, or from K to L, 

 in the lower part thereof; because from the joint 

 action of these two forces it must always de- 

 scribe equal areas in equal times throughout 

 its annual course. These areas are represented 

 by the triangles B S C, C S D, D S E, E S F, &c. 

 whose contents are equal to one another from the 

 properties of the ellipsis. 



We have now given a genera] idea of the solar 

 system ; we shall next describe the bodies that 

 compose it. 



The Sim was long considered, from its constant 

 emanation of heat and light, as an immense globe 

 of fire. When viewed through a telescope, several 

 dark spots are visible on its surface, which are of 

 various sizes and durations. From the motion of 

 these spots, the sun has been found to move round 

 its axis, and its axis is found to be inclined to the 

 ecliptic. 



Various opinions have been formed respecting 

 these spots ; they have been considered as opaque 

 islands in the liquid igneous matter, and by some as 

 pits or cavities in the body of the sun. In 1788, 

 Mr. King published a dissertation on the sun, in 

 which he advanced, that the real body of the sun 

 is less than its apparent diameter ; that we never 

 discern the real body of the sun itself, except 

 when we behold its spots ; that the sun is inha- 

 bited as well as our earth, and is not necessarily 

 subject to burning heat, and that there is in reality 



