CHAPTEBS ON THE STABS. 387 



length 343 c. m. Two sets of plates are taken, one to include all the 

 stars that the instrument will photograph near poles, and the other only 

 to take in those to the eleventh magnitude. Of the latter it is intended 

 to prepare a catalogue. Some portions of the German and English cata- 

 logues have already heen published, and their results will be made use 

 of in the course of the present work. 



NUMBERING THE STARS. 



Closely connected with the work of cataloguing the stars is that of 

 enumerating them. In view of what may possibly be associated with 

 any one star — planets with intellectual beings inhabiting them — the 

 question how many stars there are in the heavens is one of perennial 

 interest. But beyond the general statement we have already made, this 

 question does not admit of even an approximate answer. The question 

 which we should be able to answer is this: How many stars are there 

 of each easily visible magnitude? How many of the first magnitude, 

 of the second, of the third, and so on to the smallest that have been 

 measured? Even in this form we cannot answer the question in a way 

 which is at the same time precise and satisfactory. One magnitude 

 merges into another by insensible gradations, so that no two observers 

 will agree as to where the line should be drawn between them. The 

 difficulty is enhanced by the modern system — very necessary, it is true — 

 of regarding magnitude as a continuously varying quantity and esti- 

 mating it with all possible precision. In adjusting the new system to 

 the old one, it may be assumed that an average star of any given mag- 

 nitude on the old system would be designated by the corresponding 

 number on the new system. For example, an average star of the fourth 

 magnitude would be called 4.0; one of the fifth, 5.0, etc. Then the 

 brightest stars, which formerly were called of the fourth magnitude, 

 would now be, if the estimate were earned to hundredths, 3.50, while 

 the faintest would be 4.50. What were formerly called stars of the fifth 

 magnitude would range from 4.50 to 5.50, and so on. But we have 

 meet with a difficulty when we come to the sixth magnitude. On the 

 modern system, magnitude 6.0 represents the faintest star visible to the 

 naked eye; but the stars formerly included in this class would, on the 

 average, be somewhat brighter than this, because none could be cata- 

 logued except those so visible. 



The most complete enumeration of the lucid stars by magnitudes 

 has been made by Pickering ('Annals of the Harvard Observatory,' Vol. 

 XIV). The stars were classified by half magnitudes, calling 



M. M. 



Mag. 2.0 all from 1.75 to 2.25 



2.5 " " 2.25 to 2.75 



etc., etc. 



For the northern stars Pickering used the Harvard Photometry; for 



