A REFRACTING TELESCOPE WITH A FLUID CONCAVE LENS. 
39 
same diameter, of plate and flint glass ; and this surely is a consideration which 
ought to have some weight, and encourage a perseverance in the principle of 
construction. 
The telescope and the particulars relative to it being thus described, it only 
remains for me to state the tests to which I have subjected it, and its per- 
formance in those cases. 
The first observations of this kind are commonly on Polaris ; the small star 
here is of course brilliant and distinct ; it is seen best with a power of 120, but 
is visible with a power of 700 . 
The small star in Aldebaran is very distinct with a power of 120. 
The small star in a Lyrse is distinctly visible with the same power. 
The small star called by Mr. Herschel Debilissima, between 4 s and 5 Lyrae, 
— whose existence, he says, could not even be suspected in either the 5 or 7- 
feet equatorial, and invisible also with the 7 and 10-feet reflectors of 6 and 9 
inches aperture, but seen double with the 20-feet reflector, — is seen very satis- 
factorily double with this telescope. 
7] Persei, marked as double in South and Herschel’s catalogue at the 
distance of 28", with another small star at the distance of 3' 57" both n p, is 
seen distinctly sixfold, four of the small stars being within a considerably less 
distance than the remote one of r\ marked in the catalogue : and rejecting this 
remote star, the principal and the other four small stars form a miniature 
representation of Jupiter and his Satellites, three of them being nearly in a line 
on one side, and the other on the opposite : there are also other small stars 
within the same distance, but the most remarkable are those arranged in a line 
as above stated. 
A number of other small stars which are spoken of as difficult to observe 
from their minuteness, are seen more or less distinctly with this instrument. 
Amongst the closer and larger stars I have tried the telescope upon those 
commonly selected as tests, viz. 
Castor; which is distinctly double with 120, and well opened and stars per- 
fectly round with 360 and 700. 
y Leonis and « Piscium are seen, with the same powers, equally round and 
distinct. 
