Double and Triple Stars. 283 



n Lyra. A small blue star, was much improved by illumi- 

 nation. 



/ Trianguli. A small blue star, bears illumination very 

 well. 



-n Persei. A small and extremely faint blue star, bears 

 illumination well. 



59 Serpentis. A small blue star of the 9th mag. bears 

 all the illumination. 



22 Monocerotis. A small star, bears the illumination well, 

 while a small white star near it bears it ill. 



6 Virginis. The extremely faint small star bears a good 

 illumination. 



51 Piscium. This star, of a ruddy plum colour, bears a 

 very bad illumination in proportion to its size. 



When the stars under examination had the last degree of 

 faintness, Mr Herschel and Mr South resorted to a singular 

 method of obtaining a view of them, and even a rough mea- 

 sure of the angle of position. They directed the eye to another 

 part of the field. In this way, a faint star in the neighbour- 

 hood of a large one will often become very conspicuous, so as 

 to bear a certain illumination, which will yet totally disap- 

 pear, as if suddenly blotted out, when the eye is turned full 

 upon it, and so on, appearing and disappearing alternately, as 

 often as we please. The small companion of 23 (h) Ursa? 

 Majoris, is a remarkable instance of this, and also £ Persei ; 

 7 Tauri ; 43 Persei ; / Leporis (R. Asc. 5 h . 4 m .) ; 63 Gemi- 

 norum. " The lateral portions of the retina," our author re- 

 marks, " less fatigued by strong lights, and less exhausted 

 by perpetual attention, are probably more sensible to faint 

 impressions than the central ones, which may serve to account 

 for this phenomenon." 



The explanation here given of this curious phenomenon is, 

 we apprehend, not well founded ; but as the subject is a very 

 interesting one, we shall make it the subject of the next 

 article. 



