384 POPULAR SCIENCE MONTHLY. 



himself to the northern hemisphere, but extended his list over the 

 whole celestial sphere, from the north to the south pole. 



The catalogue of the celebrated Tycho Brahe, prepared toward the 

 end of the sixteenth century, though of great historic value, is of no 

 special interest to the general reader at the present time. A supple- 

 ment to it, continuing its list of stars to the south pole, was published 

 by Halley, who made the necessary observations during a journey to 

 St. Helena in 1677. 



The catalogue of Hevelius, published in 1690, offers no feature of 

 special interest, except the addition of several new constellations which 

 he placed between those already known. Having the aid of the tele- 

 scope, he was able to include in his catalogue stars which had been 

 invisible to his predecessors. 



Modern catalogues of the stars may be divided into two classes: 

 Those which include only stars of a special class, or stars of which the 

 observer sought to determine the position or magnitude with all attain- 

 able precision; and catalogues intended to include all the stars in any 

 given region of the heavens, down to some fixed order of magnitude. 

 It may appear remarkable that no attempt of the latter sort was seriously 

 made until more than two centuries after the telescope had been pointed 

 at the heavens by Galileo. A reason for the absence of such an attempt 

 will be seen in the vast number of stars shown by the telescope, the 

 difficulty of stopping at any given point, and the seeming impossibility 

 of assigning positions to hundreds of thousands of stars. The latter 

 difficulty was overcome by the improved methods of observation devised 

 in modern times. 



About the middle of the present century the celebrated Argelander 

 commenced the work of actually cataloguing all the stars of the north- 

 ern celestial hemisphere to magnitude 9-J. This work was termed a 

 Durchmusterung of the northern heavens, a term which has been intro- 

 duced into astronomy generally to designate a catalogue in which all the 

 stars down to a certain magnitude are supposed to be mustered, as if a 

 census of them were taken. The work fills three quarto volumes and 

 contains more than 310,000 stars, of each of which the magnitude and 

 the right ascension and declination are given. This work was extended 

 by Schonfeld, Argelander's assistant and successor, to 22° of south 

 declination. 



In the latitudes in which most of the great observatories of the 

 world are situated, that part of the celestial sphere within 40° or 50° of 

 the south pole always remains below the horizon. Around this invisible 

 region a belt of somewhat indefinite breadth, 10° or more, can be 

 only imperfectly observed, owing to the nearness of the stars to the 

 horizon, and the brevity of the period between their rising and setting. 

 Up to the middle of the nineteenth century, the few observatories 



