MOTION OF THE SUN. 19 



sun revolving around it in a circular orbit, and the stars still fur- 

 ther beyond. Now on the supposition that this is the true system 

 of the world, suppose the suii revolving in the direction A B, and 

 an observer at a, facing towards the north N. He would perceive 

 the sun appear to rise at his right hand, or in the east, and when 

 the sun had travelled far enough round, say to B, to become 

 visible to an observer at b, he would see it at his right hand, or hi 

 the east. The sun in his daily revolution, would thus track out in 

 the heavens a certain line, which astronomers call a diurnal circle. 

 Now suppose that some morning, just at sunrise, we observe 

 a particular star, A, close to the sun, rising just before it. If the 

 stars revolved around the earth in the same time as the sun, as 

 they seem to do from a casual observation, it is evident that after 

 any definite interval, say one month, the sun and this star would 

 still be found together, but this is not the case, for after one month, 

 it will be found, that this star A, which rose just before the sun, 

 will now rise two hours before him, and the sun will be near the 

 star C, having apparently moved backward the distance A C. If 

 we should continue to observe this backward motion of the sun, 

 we would find that after one year had elapsed, the sun would have 

 moved completely around backward, contrary to the direction in 

 which, each day he seems to move across the heavens, arriving 

 again at A. Hence it would appear, that, the earth being the 

 centre, the stars are revolving around it a little faster than the sun, 

 but in the same direction, gaining upon the sun about 4 minutes 

 a day, so that in one month the star A would gain 120 minutes or 

 two hours, and rise just so much sooner than the sun ; and thus, 

 in the course of a year, the stars would make one more revolution 

 than the sun. Now suppose we were to observe carefully the 

 stars near and over which the sun passed in this backward motion, 

 for it is evident that this path would mark out a circle in the 

 heavens. Astronomers have done this, and they call this path or 

 line, which has a fixed position among the stars, the Ecliptic, or 

 sun's path. On the next page we represent the ecliptic, and a certain 

 space on each side of it. This space includes the orbits of all the 

 planets, which also partake of the same backward motion as the.sun. 



