40 Solar System* 



the orbits of all the planets and comets, 

 and turns round his axis in 25 days 6 

 hours, as is evident by the motion of 

 spots seen on his surface. By the vari- 

 ous attractions of the circumvolving plan- 

 ets, he is agitated by a small motion 

 round the center of gravity of the system. 

 Let us suppose the earth's orbit to be 

 a thin, even, solid plane ; cutting the sun 

 through the center, and extended out as 

 far as the starry heavens, where it will 

 mark the great circle called the Ecliptic. 

 This circle we suppose to be divided into 

 12 equal parts, called Signs ; each sign 

 into 30 equal parts, called Degrees ; each 

 degree into 6O equal parts called Minutes ; 

 and every minute into GO equal parts, 

 called Seconds ; so that a second is the 

 60th part of a minute ; a minute the 60th 

 part of a degree ; and a degree the 360th 

 part of a circle, or 30th part of a Sign. 

 The ^lanes of the orbits of all the other 



ova! ellipsis will be described ; the two points 

 where the pins are fixed being 1 called the foci or 

 focuses thereof. The orbits of all the planets are 

 elliptical, and the sun is placed in or near one of 

 the foci of each of them ; and that in which he is 

 placed is called the lower focus. 



