THE AXIS AND POLE. . 



7. This circumstance of the unaltered configuration and rela- 

 tive positions of this multitude of objects scattered over the firma- 

 ment, suggests irresistibly the idea, that the motion of revolution 

 described above, in which they all participate, is not a motion 

 proper to each separate and independent object, but one which 

 belongs to the firmament itself, upon which they appear as if 

 they were fixed. In short, the firmament presents the aspect of 

 a hollow sphere of vast dimensions, in the centre of which the 

 observer is placed, and upon the surface of which the countless 

 multitudes of objects which he beholds are fixed. This stu- 

 pendous sphere appears to have a motion of revolution on a certain 

 diameter as an axis, making a complete revolution once in twenty- 

 four hours. The diameter round which it revolves, or appears to 

 revolve, is directed to a certain point of the northern quadrant of 

 the meridian, the altitude of which above the horizon of the 

 observer, will be always found to be exactly equal to the latitude 

 of his station. This motion of revolution of the firmament, carry- 

 ing with it the numerous objects seen upon it, will perfectly 

 explain all the appearances above described, and many others. 

 Thus, it is evident that all objects on the celestial sphere must be 

 moved in circles parallel one to another round its axis ; and that 

 these circles become gradually less as the object is nearer to the 

 pole. When the observer looks to the south, the circles described 

 by the objects are partly above and partly below the horizon; 

 and, consequently, all such objects alternately rise and set. But 

 when he looks to the north, the chief part of the objects which he 

 beholds being nearer to the extremity of the axis round which 

 the sphere is carried, describe circles smaller and smaller, which, 

 being entirely above the horizon, the objects in them neither rise 

 nor set. 



8. From what has been stated, it will be obvious, that an object 

 placed precisely at that point of the meridian at which the axis 

 round which the sphere turns terminates, would be immoveable ; 

 and would evidently be the only immoveable object in the visible 

 firmament. It does so happen, that there actually is no star pre- 

 cisely at that point ; but there is a rather conspicuous one so near 

 to it, that although it moves round it in a small circle, the diameter 

 of which is about six times that of the full moon, such motion can 

 only be ascertained by astronomical instruments ; and therefore, 

 for all the purposes of common observation, the star in question 

 may be regarded as stationary, and as indicating the position of 

 the northern extremity of the axis on which the celestial sphere 

 appears to revolve. 



This point of the sphere is called its pole ; and as there is a 

 corresponding point at the other extremity of the axis, which is 



149 



