LECTURE XVIII. 



ASTRONOMY. 



OF THE SUN, AND HIS REAL AND APPARENT 

 MOTIONS. 



THE sun with the planets and comets which 

 move round him as their centre constitute what 

 is called the solar system. Those planets which 

 are near the sun not only finish their circuits 

 sooner, but likewise move faster in their re- 

 spective orbits than those which are more remote 

 from him. Their motions are all performed 

 from west to east in orbits nearly circular, but 

 in truth elliptical, except so far as they are 

 effected by each other's disturbing forces. 



The sun, the centre of the system, has been 

 generally considered as composed of the matter 

 of light and heat, whether these are to be re- 

 garded as essentially the same or not; perhaps 

 it will be speaking more correctly to say, that 

 he is the source of both, and that he both warms 

 and enlightens the bodies which surround him, 

 probably by means of perpetual emanations from 

 a luminous atmosphere. The sun has two ap- 

 parent motions, the diurnal and the annual. In 

 the first he appears to revolve round the earth 



