280 FERGUSON'S LECTURES. 



LECT. studs to be of different magnitudes, and placed at the 

 Xx^x^' same angular distance from each other as the stars are 

 the sphere will be a true representation of the starry 

 heaven, to an eye supposed to be in its center, and 

 viewing it all around. And if a small globe, with a 

 map of the earth upon it, be placed on an axis in the 

 center of this starry sphere, and the sphere be made to 

 turn round on this axis, it will represent the apparent 

 motion of the heaven round the earth. 



If a great circle be so drawn upon this sphere as to di- 

 vide it into two equal parts, or hemispheres, and the 

 plane of the circle be perpendicular to the axis of the 

 The equi- sphere, this circle will represent the equinoctial, which 

 noctiai, divides the heavens into two equal parts, called the 

 northern and the southern hemispheres; and every point 

 The poles. f that c i rc l e w iU De equally distant from the poles, or 

 ends of the axis in the sphere. That pole which is in 

 the middle of the northern hemisphere, will be called 

 the north pole of the sphere, and that which is in 

 the middle of the southern hemisphere, the south 

 pole. 



If another great circle by drawn upon the sphere, in 

 in such a manner as to cut the equinoctial at an angle 

 of23j degrees in two opposite points, it will represent 

 The ecllp- the ecliptic, or circle of the sun's apparent annual motion ; 

 one half of which is on the north side of the equinoctial, 

 and the other half on the south. 



If a large stud be made to move eastward in this 

 ecliptic in such a manner as to go quite round it, in the 

 time that the sphere is turned round westward 366 

 The sun. times upon its axis ; this stud will represent the sun, 

 changing his place every day a 365th part of the eclip- 

 tic ; and going round westward, the same way as the 

 stars do ; but with a motion so much slower than the 

 motion of the stars, that they will make 366 revolu- 

 tions about the axis of the sphere, in the time that the 



