NOTES. 



Seidel attempted to determine with SteinheiTs pftotometer the quantities of 

 light of several stars of the 1st magnitude which appear at sufficient altitudes in 

 our northern hemisphere. He makes a Lyrse = 1, and then finds Sirius == 

 5'13; Rigel, whose brightness seems to be increasing, = 1'30; Arcttirus, 

 0-84 ; Capella, 0'83 ; Procyon, O'?l ; Spica, 0'49 ; Atair, 0'40 ; Aldebaraa 

 0'36; Deneb, 0-35; Regulus, 0'34 ; Pollux, 0'30 ; Betelgeuze is left out, 

 because it is variable, as appeared particularly between 1836 and 1839 

 (Outlines, p. 523). 



( 158 ) p. 83. For the numerical bases of the photometric results, compare 

 four tables of Sir John Herschel, in his Cape Observations (a. p. 341 ; b. 

 p. 367 371 ; c. p. 440 ; and d. in his Outlines of Astronomy, p. 522 

 525, and 645 646). For a mere arrangement in order of magnitude 

 or brightness, but without any numbers being expressed, see the Manual of ' 

 Scientific Enquiry prepared for the Use of the Navy, 1849, p. 12. In order 

 to render more complete the conventional language which has been hitherto 

 used (i. e, the old classification into magnitudes), Sir John Herschel, in the 

 Outlines of Astronomy, p. 645, has appended to the vulgar scale of magni- 

 tudes, a scale of photometric magnitudes obtained merely by the addition of 

 0*41, as is more fully explained in the Cape Observations, p. 370. I subjoin 

 such a table, combining in it the stars of the Northern and Southern Hemi- 

 spheres without distinction. See p. xlii. to p. xlv. at the close of the Notes 

 belonging to this section. 



( 159 ) p. 83. Argelander, Durchmnsterung des nordl. Himrnels zwisehen 

 45 und 80 Decl. 1846, S. xxiv. xxvi. ; Sir John Herschel, Ast, Obs. at 

 the Cape of Good Hope, p. 327, 340, and 365. 



( 16 ) p. 83. Same work, p. 304 ; and Outlines, p. 522. 



( 161 ) p. 84. Phil. Trans. Vol. Ivii. for the year 1767, p. 234. 



( 162 ) p. 84. Wollastou's comparison of the light of the Sun and of the 

 Moon was made in 1799, and was based on shadows cast by wax-lights, while 

 in the experiments with Sirius in 1826 and 1827 images reflected from a 

 glass-globe were employed. The earlier assigned ratios of the intensity of the 

 solar light as compared to that of the Moon differ very much from the results 

 here given. Michel! and Euler, proceeding from theoretical grounds, had 

 respectively concluded 450000 and 374000 to 1. Bouguer, from measurements 

 of the shadows of wax-lights, had even made it only 300000 to 1. Lambert 

 considers the light of Venus, when at the brightest, to be 3000 fainter than 

 that of the full Moon. According to Steinheil, the Sun would require to be 

 3286500 times further off than it is in order to appear to the inhabitants of 



