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 heing 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 g 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. 



}] 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 ri 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. 



7 Leonis and a Piscium are seen, with the same powers, equally round and 

 distinct. 



