76 ASTRONOMY. 
planets Ceres, Pallas, Juno, and Vesta, by Piazzi, Olbers, and Harding. 
Lalande, Bode, but especially Maskelyne and Piazzi, prepared fuller and 
more accurate catalogues of the fixed stars. Gauss taught new and very 
ingenious methods of accurately computing the planetary orbits, while 
Bessel attained the reputation of one of the greatest theoretical and prac- 
tical astronomers that ever lived. During this time, however, the art of 
constructing astronomical instruments and achromatic telescopes was not 
behindhand, as the names of a Dollond, Ramsden, Troughton, Reichenbach, 
Fraunhofer, Repsold, and others, can satisfactorily testify. Finally, in later 
times, the appropriate and well arranged observatories at Altona, Berlin, 
Gottingen, Greenwich, Helsingfors, Kénigsberg, Ofen, Paris, Pulkowa, 
Seeberg, Vienna, &c., have been erected, and three new planets discovered 
—Astrea, Neptune, and Iris—and the existence of a central sun has been 
indicated by Madler. Our century can point to a mass of accurate obser- 
vations which have already been employed by theoretical astronomy to such 
account, that the science of the stars has been raised to a giant height, 
almost to entire perfection—a perfection which hardly any other branch of 
human knowledge can boast. 
I. SPHERICAL ASTRONOMY. 
The Armillary Sphere; the most important Points, Circles, and Terms 
in the Celestial Sphere. 
THE ARMILLARY SPHERE. 
1. The ancients at an early period imagined the existence of certain 
points, circles, &c., on the sphere of the heavens, by means of which they 
might the more readily comprehend, and be the better able to follow the 
various celestial phenomena. They also invented an instrument, the 
armillary sphere, partly with the view of giving an intelligible exhibition 
of the mutual relation of these points and circles, and of the axis of the 
heavenly motions, and partly to make actual observations by means of this 
sphere. The armillary sphere (pl. 6, fig. 1) consists of a frame, with a 
horizon on which are represented the 360 degrees, the regions of the heavens, 
the calendar, and the height of the sun for every day in the year. Two 
notches in the horizontal circle, and corresponding to its north and south 
points, receive the fixed meridian, whose plane is perpendicular to, and 
centre coincident with that of the horizontal circle. This meridian, 
within which the other circles as well as the small terrestrial globe may all 
be rotated together on the common axis of the heavens and earth, can be 
moved in these notches, still remaining in the original vertical plane; in 
this manner the general axis may be placed at various angular distances 
with the horizon. The centre of the small terrestrial globe is coincident 
with that of the general armillary sphere, the names and position of the 
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