440 THE POPULAR SCIENCE MONTHLY. 



der, at Bonn, sets down in his charts no less than 3,250 stars visible 

 to the naked eye ; and Heis, whose eye indeed was possessed of an 

 abnormal power, seeing stars as points without rays, increased Ar- 

 gelander's list by 2,000 stars visible at Minister. Thus, not taking 

 into the account the no less than twenty more degrees of the heavens 

 visible from Alexandria than from Germany, the ancients noted 

 hardly one-half of the stars which were visible to them ! The defec- 

 tiveness of their observations can be more easily understood from the 

 fact that for instance they reckoned 474 stars of the fourth magnitude, 

 only 271 of the fifth, and finally only 49 of the sixth magnitude; 

 whereas the fact is, that the number of stars increases so rapidly in 

 the order of magnitudes that each succeeding class embraces a much 

 larger number than all the classes that precede it. In our latitudes 

 Argelander makes out with the naked eye nineteen nebulae and star- 

 clusters, while Hipparchus mentions only two, and Ptolemy five, nei- 

 ther of them noting such prominent objects as the nebula in Orion 

 and that in Andromeda. And such defective knowledge as this 

 of the open-lying heavens persisted long after the invention of the 

 telescope for full 1,500 years. Among the old astronomers the Per- 

 sian, Abdalrahman-Al-Siiri, who lived in the tenth century, forms a 

 notable exception ; but he did not inspire his contemporaries or his 

 successors with his own ardor, or prompt them to add to his labors. 



The same is to be said of the southern heavens. The Arabians, 

 surely, did not lack opportunity for acquiring a knowledge of many 

 of its constellations. Ever since the days of Bartolomeo Diaz, it was 

 a necessity for Europeans, on sea-voyages, to determine places by 

 southern constellations. Ptolemy was acquainted with only a few of 

 the principal stars of the antarctic hemisphere, and it was not till the 

 beginning of the seventeenth century that Theodor von Emden regu- 

 larly divided these regions of the heavens into constellations. It re- 

 mained for Herschel, in recent times, to determine a number of open 

 questions with regard to these southern constellations. 



To account for this backwardness in the investigation of a subject 

 which certainly possessed at least as much interest for the ancients as 

 for ourselves, by declaring it to be the result of their superficiality, 

 were an injustice to the olden time, seeing that in other respects it 

 commands our unconditional admiration for its arduous achievements. 

 That what they needed was to have their senses trained to this kind 

 of work, and that, although they had keen appreciation of art, they 

 never learned to look at things with the eye of the investigator of 

 Mature, will be better understood from a statement of what they 

 knew about individual celestial objects than of what they knew about 

 the entire firmament. 



That well-known group of stars, the Pleiades, which in the Fall 

 adorns our eastern sky by night, serves well to show that in observing 

 the stars something else is required besides a clear atmosphere and 



