fo Penetration into Space hy TeUfcopes, 



" With a fliagnifylng power of 157, it appears extremely bright, round, and cafily re- 

 " folvable. With 300, 1 can fee the ftars. It rcfembled the clufter of ftars taken at 16'' 

 " 43' 40" *, which probably would put on the fame appearance as this, if it were at a dif- 

 •* tance half as far again as it is. R A I'j*' 26' 19"; PD 93° 10." 



Here we may compare two obfervations j one taken with the penetrating power of 39, 

 the other with 75 ; and, although the former inftrument had far the advantage in magni- 

 fying power, the latter certainly gave a more complete view of the objeft. 



The 20-feet reflector having been changed from the Newtonian form to my prefent one, 

 I had a very ftriking inftance of the great advantage of the increafed penetrating power, in 

 the difcovery of 'the Georgian fatellites. The improvement, by laying afide the fmall 

 mirror, wag from 61 to 75 : and, whereas the former was not fufficient to reach thefe faint 

 objeftg, the latter fhewed them perfectly well. 



March 14, 1798. I viewed the Georgian planet with a new 25-feet refle^lor. Its pc- 



^/ ,64 X 2401 

 netrating power is " — 95,'e5; and, having juft b«fore alfo viewed it with 



my 20-feet inftrument, I found, that with an equal magnifying power of 300, the 25-fcet 

 telefcope had confiderably the advantage of the former. 



Feb. 24, 1786. I viewed the nebula near Flamfteed's 5th Serpentis, which has been 

 mentioned before, with my 20-feet refle£lor ; magnifying power 157. 



*' The moft beautiful extremely compreffed clufter of fmall ftars 5 the greateft part of 

 " them gathered togetlicr into one brilliant nucleus, evidently confifting of ftars, fur- 

 " rounded with many detached gathering ftars of the fame fize and colour. RA IS^Y 

 " 12"; PD87°8'." 



May 27, 1 79 1. I viewed the fame objefl: with my 40-feet telefcope; penetrating 



V 564x480 " ^ .f . 



power — ' = 191,09; magnifymg power 370. 



2 . 



" A beautiful clufter of ftars. I counted about 200 of them. The middle of it Is fo 

 " compreffed that it is impoffible to diftinguifli the ftars." 



Here it appears, that the fuperior penetrating power of the 40-feet telefcope enabled 

 me even to count the ftars of this nebula. It is alfo to be noticed, that the objeft did not 

 ftrike me as uncommonly beautiful ; becaufe, with much more than double the penetrating, 

 and alfo more than double the magnifying power, the ftars could not appear fo compreffed 

 and fmall as in the 20-feet inftrument : this, very naturally, muft give it more the refem- 

 blance of a coarfer clufter of ftars, fuch as I had been in the habit of feeing frequently. 



• The objeft referred to is No. la. of the Connoijfance des Temps for 1783, called " Nebuleufe fans 

 *' etoiles." My defcription of it is, " A very beautiful, and extremely compreffed, clufter of ftars ; the 

 " moft compreffed part about 3 or 4' ip diameter. R A le*" 46' z" 5 P D 93° 4S'." 



The 



