ASTRONOMY. 



two additional satellites to Saturn, of which 

 the number is now seven; a new method 

 of measuring the lunar mountains; the ro- 

 tation of the planets on their axis ; on the 

 parallax of the fixed stars ; catalogues of 

 double, triple stars, &c. ; of nebulae ; and 

 of the proper motion of the sun and so- 

 lar system ; the accounts of which, tog-e- 

 ther with many other valuable papers, he 

 has communicated, from time to time, in 

 different parts of the Philosophical Trans- 

 actions. Anew planet has been disco- 

 vered by M. Piazzi, of Palermo, between 

 Mars and Jupiter, to which has been 

 given the name of Ceres FerdSnanclia ; 

 another by Dr. Olbers ; a third and a 

 fourth have also been discovered, which 

 we shall briefly notice farther on. 



M THE APPARENT MOTIONS OP THE HEA- 

 VENLY BODIES. 



Having 1 given a very brief sketch of the 

 history of this science, than which, few, 

 if any, have higher claims to our venera- 

 tion and regard, we proceed to consider 

 the science itself, intending to present the 

 reader with a popular outline of the stu- 

 dy, freed as much as possible from ma- 

 thematical principles, upon which it de- 

 pends, but for which few, in comparison, 

 can be supposed, from previous studies, 

 to ha\ e any taste. 



When we cast our eyes towards the 

 heavens, we perceive a vast concave he- 

 misphere, at an unknown distance, of 

 which the eye seems to constitute the 

 centre. The earth stretches at our feet 

 like an immense plain, and appears to 

 meet, and to bound, the heavenly hemis- 

 phere. The circle around, where the 

 earth and heavens seem to meet and 

 touch each other, is called the horizon. 

 It is natural to imagine, that, besides the 

 hemisphere which we perceive, there is 

 another, exactly similar, concealed from 

 our view by the earth, and that the earth 

 therefore is suspended in the middle of 

 this heavenly sphere, with all its inhabi- 

 tants. A little observation turns this sus- 

 picion into certainty; for in a clear even- 

 ing the heavenly hemisphere is seen 

 Studded with stars, and its appearance is 

 changing every instant. New stars are 

 continually rising in the east, while others 

 are setting in the west. Those stars, that 

 early in theevening are seen just above the 

 eastern horizon,will at midnight be seen in 

 the middle of the starry hemisphere, and 

 may be traced moving gradually towards 

 the west, till at length they sink below 

 the horizon. If we look to the north, we 



perceive that many stars in that quarter 

 never set at all, "but move round and 

 round, describing a complete circle in 24 

 hours : these describe their circles round 

 a fixed point in the heavens, and the circles 

 diminish more and more the nearer the 

 star is to that point. This fixed point is 

 called the north pole. There must be a 

 similar fixed point in the southern hemis- 

 phere, called the south pole. In this wav 

 theheavenly sphere appears to turn round- 

 two fixed points, called the poles, once 

 in every 24 hours. The imaginary line 

 which joints the points is called the axis 

 of the world. We shall endeavour to il- 

 lustrate this by means of a figure. 



Let H O (fig 1. Plate II.) represent the 

 circle of the horizon, seen edgeways, 

 when it will appear as a straight line : 

 let H P E R Q represent the complete 

 sphere of the heavens, of which H M'O is 

 supposed to be the visible hemisphere, 

 and H N O the invisible hemisphere : then 

 P will be the pole or fixed point among 

 the stars, visible to us, round which they 

 all appear to turn, and will be the oppo- 

 site pole ; the line P R will be the axis of 

 the sphere. 



To obtain precise views of the motions 

 of the heavenly bodies, it is necessary to 

 be able to assign precisely the place in 

 which they are. This is done by means 

 of several imaginary lines or circles, sup- 

 posed to be described upon the surface 

 of the sphere. These circles are divided 

 into degrees, minutes, and seconds. The 

 great circle of the sphere, Q E, which is 

 perpendicular to the axis of the world, 

 and of course 90 distant from either pole, 

 is called the equator. The smaller cir- 

 cles which the stars describe, in conse- 

 quence of their apparent diurnal motions, 

 are called parallels, because they are pa- 

 rallel to the equator. The equator di- 

 vides the heavenly sphere into two equal 

 parts, the north and south ; but, to be 

 able to assign the position of the stars, it 

 is necessary to have another circle pass- 

 ing through the poles, and cutting the 

 equator perpendicularly ; this is called 

 the meridian, which is supposed to pass 

 through the poles, and also directly over 

 the head of the observer, M, and the 

 point, N, exactly opposite to that. The 

 first of these points is called the zenith, 

 and the second is denominated the nadir. 

 The meridian divides the circles describ- 

 ed by the stars into two equal parts, and 

 when they reach it, they are either at 

 their greatest height above the horizon,, 

 or they are at their least height. The si- 

 tuation of the pole is readily found, it fee- 



