penetrating into Space by Telescopes. 75 



" which probably would put on the same appearance as this, 

 " if it were at a distance half as far again as it is. RA 17 11 26' 

 "19"; PD93 10'." 



Here we may compare two observations ; one taken with the 

 penetrating power of sg, the Other with 75 ; and, although the 

 former instrument had far the advantage in magnifying power, 

 the latter certainly gave a more complete view of the object. 



The 20-feet reflector having been changed from the New- 

 tonian form to my present one, I had a very striking instance 

 of the great advantage of the increased penetrating power, in 

 the discovery of the Georgian satellites. The improvement, by 

 laying aside the small mirror, was from 61 to 7,5 ; and, whereas 

 the former was not sufficient to reach these faint objects, the 

 latter shewed them perfectly well. 



March 14, 1798. I viewed the Georgian planet with a new 



V .64 x 



25-feet reflector. Its penetrating power is ' 4 — i— -= 95,85; 



and, having just before also viewed it with my^ 20-feet instru- 

 ment, I found, that with an equal magnifying power of 300, the 

 25-feet telescope had considerably the advantage of the former. 



Feb. 24, 1786. I viewed the nebula near Flamsteed's 5th 

 Serpentis, which has been mentioned before, with my 20-feet 

 reflector; magnifying power 157. 



" The most beautiful extremely compressed cluster of small 

 " stars ; the greatest part of them gathered together into one 

 " brilliant nucleus, evidently consisting of stars, surrounded 

 " with many detached gathering stars of the same size and 

 " colour. RA 15 11 7' 12"; PD 87 8'." 



May 27, 1791. I viewed the same object with my 40-feet 



L 2 



