540 



than in those which are naturally coloured. All these cir- 

 cumstances, if I be not mistaken, agree with observation." 



NOTE C. 



In following the method I have indicated (Chap. X, p. 

 328 of the present volume) for estimating the intensity of 

 the light of the stars, there is no reason to fear, that a 

 change of inclination in the mirrors should have any sensible 

 influence on the quantity of light reflected. This influence is, 

 without doubt, considerable, when light is reflected by a 

 transparent glass $ but it is almost null, when the rays are 

 reflected by a glass silvered on the back. Hence it follows, 

 that, in order to compare two stars, and equalize their light, 

 we can bring into the field of the telescope such as are at 

 very considerable angular distances. The following are the 

 results of my investigations, placing on the astrometer stars 

 of the first magnitude, between 80* and 100° j those of the 

 second magnitude, between 60° and 80° j those of the third, 

 between 45° and 60° j those of the fourth, between 30° and 

 45° 5 and those of the fifth, between 20° and 30°. 



Sirius - - - 



- 100° 



Canopus - - 



r 98 



ec Centauri - 



- 96 



Achernar - - 



- 94 



/3 Centauri - - 



- 93 



Fomalhaut - - 



- 92 



Rigel - 



- 90 



Procyon - - - 



- 88 



Betelgueuse - - 



- 86 



e Canis majoris 



- 83 



1 - - - - - 



- 81 



a Gruis - - - 



- 81 



