distances and positions of 380 double and triple stars , &c. 15 
measure, especially when the two stars, as in the above in- 
stances, differ greatly in colour. 
The requisite degree of illumination is a matter of great 
consequence, and differs in almost each particular star. In 
relation to this, a singular phenomenon deserves mention. 
Many very minute stars bear, without extinction, strong de- 
grees of illumination, and are even seen the better for it, while 
others, apparently brighter, have been found unable to bear 
even the slightest extraneous light. This may probably be 
owing to an excess of blue light in the star, forming a con- 
trast with the ruddy tint of the lamp illumination : at least, 
the most remarkable instances* of the phenomenon in ques- 
tion are, those in which the small star is decidedly of a blue 
colour. 
A rather singular method of obtaining a view, and even a 
rough measure of the angles of stars of the last degree of 
faintness, has often been resorted to, viz. to direct the eye 
to another part of the field. In this way, a faint star in the 
neighbourhood of a large one, will often become very con- 
spicuous, so as to bear a certain illumination, which will yet 
totally disappear , as if suddenly blotted out, when the eye is 
turned full upon it, and so on, appearing and disappearing 
* 9 Scorpii is much improved by illumination. 
n Lyra. Small star blue. Much improved by strong illumination. 
• Trianguli. Small star blue. Bears illumination very well. 
n Persei. S. blue. Extremely faint, yet bears illumination well. 
59 Serpentis. S. blue ; and though only of 9 m., yet bears all the illumination. 
22 Monocerotis. S. blue, and bears the illumination well, while a small white 
star near it bears it ill. 
fl Virginis. The extremely faint small star bears a good illumination. 
5 1 Piscium. S. of a ruddy plum colour, and bears a very bad illumination in 
proportion to its size (7 feet equatorial.) 
