VOL. XC.] PHILOSOPHICAL TRANSACTIONS. 5Q3 



another not far from one side, but out of the cluster; another pretty bright one; 

 and a great number of small ones." Here we have a case where the penetrating 

 power of 20 fell short, when 29 resolved the nebula completely. This object 

 requires also great magnifying power to show the stars of it well ; but that power 

 had before been tried, in the 7-feet, as far as 400, without success, and could 

 only give an indication of its being composed of stars; whereas the lower mag- 

 nifying power of 250, with a greater penetrating power, in the 10-feet instru- 

 ment, resolved the whole nebula into stars. 



May 3, 1783, I viewed the nebula between * and g Ophiuchi, discovered by Mr. 

 Messier, in 1764. " With a 10-feet reflector, and a magnifying power of 250, I 

 see several stars in it, and make no doubt a higher power and more light will 

 resolve it all into stars. This seems to be a good nebula for the purpose of 

 establishing the connection between nebulae and clusters of stars in general." — 

 June 18, 1784, the same nebula viewed with a large Newtonian 20-feet reflector; 

 penetrating power -i-y^- 43 X (188 2 — 21 2 )) = 6l.l8 ; and a magnifying power of 

 157. "A very large and very bright cluster of excessively compressed stars. The 

 stars are but just visible, and are of unequal magnitudes : the large stars are red ; 

 and the cluster is a miniature of that near Flamsteed's 42d Comas Berenices, ka 

 17 h 6 m 32 s ; pd 108° 18'." Here, a penetrating power of 2Q, with a magnifying 

 power of 250, would barely show a few stars ; when, in the other instrument, a 

 power 6l of the first sort, and only 157 of the latter, showed them completely 

 well. 



July 4, 1783, I viewed the nebula between Flamsteed's 25 and 20* Sagittarii, 

 discovered by Abraham Ihle, in 1665. " With a small 20-feet Newtonian teles- 

 cope, power 200, it is all resolved into stars, that are very small and close. There 

 must be some hundreds of them. With 350, I see the stars very plainly ; but the 

 nebula is too low in this latitude for such a power." — July 12, 1784, I viewed the 

 same nebula with a large 20-feet Newtonian reflector; power 157. "A most 

 beautiful extensive cluster of stars, of various magnitudes, very compressed in the 

 middle, and about 8' in diameter, besides the scattered ones, which do more 

 than fill the extent of the field of view * : the large stars are red ; the small ones 

 are pale red. ra 18 h 23 m 3g s ; pd 1 14° 7'." The penetrating power of the first 

 instrument was 3Q, that of the latter 6l ;. but, from the observations, it is plain 

 how much superior the effect of the latter was to that of the former, notwithstand- 

 ing the magnifying power was so much in favour of the instrument with the small 

 penetrating power. 



July 30, 1783. With a small 20-feet Newtonian reflector, I viewed the nebula 

 in the hand of Serpentarius, discovered by Mr. Messier, in 170*4. " With a 

 power of 200, I see it consists of stars. They are better visible with 300. With 

 600, they are too obscure to be distinguished, though the appearance of stars is still 

 preserved. This seems to be one of the most difficult objects to be resolved. 

 * This field, by the passage of an equatorial star, -was 15' 3". — Orig. 



VOL. XVIII. 4 G 



