74 Dr. Herschel on the Power of 



" diameter, besides the scattered ones, which do more than fill 

 " the extent of the field of view c * the large stars are red ; the 

 " small ones are pale red. RA i8 h 23' 39"; PD 114 J'." 



The penetrating power of the first instrument was 39, that 

 of the latter 61 ; but, from the observations, it is plain how 

 much superior the effect of the latter was to that of the former, 

 notwithstanding 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 1 764. 



" 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. With me, there is not a doubt remaining; but 

 " another person, in order to form a judgment, ought previously 

 " to go through all the several gradations of nebulae which I 

 " have resolved into stars." 



May 25, 1791. I viewed the same nebula with a 20-feet 

 reflector of my construction, having a penetrating power of 



^ > 6 + 2 xT ^ a = 75,08. 



" With a magnifying power of 157, it appears extremely 

 " bright, rourid, and easily resolvable. With 300, I can see the 

 " stars. It resembles the cluster of stars taken at i6 h 43' ip'Vf* 



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



f The object referred to is No. 10. of the Connoissance des Temps for 1783, called 

 «« Nebuleuse sans etoiles." My description of it is, " A very beautiful, and extremely 

 " compressed, cluster of stars : the most compressed part about 3 or 4' in diameter. 

 « RA i6 h 46' 2" ; PD 93 46'." 



