NOTES. 



PHOTOMETRIC ARRANGEMENT OE THE FIXED STARS. 



I CONCLUDE this section with a table taken from Sir John Herschel's Out- 

 lines of Astronomy (p. 645 and 646) : I am indebted for its arrangement 

 and lucid explanation to my learned friend, Dr. Galle, from whose letter to 

 myself, dated in March 1850, I subjoin the following extract : 



" The numbers in the Photometric Scale in the Outlines of Astronomy 

 are results obtained from the ' Vulgar Scale,' by an addition throughout of 0'41. 

 The author (Sir John Herschel) has arrived at these more exact determina- 

 tions of star-magnitudes by observed 'sequences' of brightness, and by the 

 combination of these observations with the average of the assigned magnitudes 

 in ordinary use (Cape Observations, p. 304 352), taking more particularly 

 the data in the Astronomical Society's Catalogue for 1827 as a basis. The 

 proper photometric results of several stars by means of the Astrometer (Cape 

 Observations, p. 353, et seq.) have not been employed directly in this table, 

 but have only served in a general way as a means of judging of the relation 

 or correspondence of the scale in common use (1st, 2d, 3d, &c. magnitudes), 

 to the real quantities of light in different stars. There has thus been found 

 the result (at all events remarkable), that the decrease of our ordinary star- 

 magnitudes (1, 2, 3 ) is approximately as if a star of the 1st magnitude 



were placed successively at distances of 1, 2, 3, whereby, according to 



photometric law, its brightness would have successively the values 1, , 



, -Jg. (Cape Observations, p. 371, 372; Outlines, p. 521, 522) ; but in 



order to make accordance still greater, it is only necessary to raise our star- 

 magnitudes, as hitherto employed, about half a magnitude (or more exactly 

 0'41) ; so that in future a star of the 2'00 magnitude should be called of the 

 2'41 magnitude; a star of 2'5 magnitude, 2'91, and so on. Sir John 

 Herschel has proposed this * photometric' (raised) scale for accept- 

 ance (Cape Obs. p. 372 ; Outl. p. 522), and his proposal will surely be 

 assented to : for, the difference from the Common or Vulgar Scale would 

 ' hardly be felt' (Cape Obs. p. 372) ; and the table in the ' Outlines 

 of Astronomy,' p. 645, et seq., may already serve as a basis as far 



