132 COSMOS. 



be inferred from the alphabetical order of the letters, and that 

 Bayer was influenced in his choice of these letters, by the 

 form and direction of the constellations. 77 



PHOTOMETRIC ARRANGEMENT OF THE FIXED STARS. 



I close this section with a table taken from Sir John 

 Herschel's Outlines of Astronomy, pp. 645 and 646. I am 

 indebted for the mode of its arrangement, and for the follow- 

 ing lucid exposition, to my learned friend Dr. Galle, from 

 whose communication, addressed to me, in March, 1850, I 

 extract the subjoined observations : 



kt The numbers of the photometric scale in the Outlines of 

 Astronomy have been obtained by adding throughout 0-41 

 to the results calculated from the vulgar scale. Sir John 

 Herschel arrived at these more exact determinations by ob- 

 serving their " sequences" of brightness, and by combining 

 these observations with the average ordinary data of magni- 

 tudes, especially on those given in the catalogue of the Astro- 

 nomical Society for the year 1827. (See Observ. at the Cape, 

 pp. 304-352.) The actual photometric measurements of seve- 

 ral stars as obtained by the Astrometer (op. cit. p. 353), have 

 not been directly employed in this catalogue, but have only 

 served generally to show the relation existing between the 

 ordinary scale (of 1st, 2nd, 3rd. &c., magnitudes) to the actual 

 photometric quantities of individual stars. This comparison 

 has given the singular result that our ordinary stellar magni- 

 tudes (1, 2, 3 . ..) decrease in about the same ratio as a star of 

 the 1st magnitude when removed to the distances of 1, 2, 3 ... 



mined, and which is seen by the naked eye in the immediate 

 vicinity of the instrument. The amount of this colour is given 

 by the inclination of the pile ; and if this portion of the appa- 

 ratus consist of the same number of plates formed of the same 

 kind of glass, observations made at different places may readily 

 be compared together." 



77 Argelander de fide Uranometrice Bayeri, 1842, pp. 14-23. 

 " In eadem classe littera prior majorem splendorem nullo modo 

 indicat" (9). Bayer did not therefore show that the light 

 of Castor was more intense in 1603 than that of Pollux. 



