10 
MR. BARLOW ON THE PERFORMANCE 
marked as double in South and Herschel’ s catalogue, with a small star at a 
greater distance ; this star is seen distinctly sextuple in my telescope. These 
stars I had the satisfaction of showing to M. Struve in his recent visit to 
England, and I have since seen them in Sir James South’s telescope. Another 
good test of the light of my telescope is found in a Orionis, marked in the 
above catalogue as two distinct sets of stars, each triple ; whereas, in my 
telescope, both sets are quadruple, with a double star, or rather two very fine 
stars between them ; the fourth star in the bright set, is a remarkably fine 
brilliant point, very near to the principal star, and in the same line as the 
nearest of the original small stars, on the opposite side, so that the three are 
in one line ; or more accurately, the line joining the two small stars touches the 
margin of the bright star. I might mention several other cases of fine double 
stars which I have discovered, but I select the above because it is evident that 
both objects have been well examined with fine instruments, and that the stars 
I have mentioned had, notwithstanding, escaped detection. 
Of the tests furnished me by Mr. Herschel I shall only select two, one of 
which in particular serves to point out in a very precise manner the limit of 
power of my telescope. This is the star (3 Capricorni, which, in the finder, is 
a coarse double star of about 3' ; but between these two stars, nearly in the 
middle, but a little below the line of junction, is a very fine double star, dis- 
covered by Mr. Herschel, and which he considers a very severe test ; he says 
indeed that he requires no other, of the light of a telescope. This star I can 
see, and, under favourable circumstances, distinctly; but still I have not suffi- 
cient command of it to see it double. We have thus the exact limit defined at 
which the light of this splendid instrument surpasses that of my telescope. 
The other object to which I have alluded is <p Virginis: this he considers a very 
easy double star, although it had before escaped detection ; it is however 
rather close. This star I could see very distinctly one evening (June 4th), the 
moon being very bright and full, on the meridian, and within an hour of the 
star. I mention this object because it requires a certain degree of defining 
power ; in point of light it involves no difficulty. Mr. Herschel could see it 
when his aperture was reduced to six inches. 
Amongst the objects which I have seen in Sir James South’s twenty-feet, 
there is also one in particular which forms a good test of the relative power of 
