Royal Irish Academy. 589 



nebula of Orion and that of Andromeda showed no appearance of 

 resolution, but the small nebula near the latter is clearly resolvable. 

 This is also the case with the ring-nebula of Lyra ; indeed, Dr. Ro- 

 binson thought it was resolved at its minor axis : the fainter nebulous 

 matter which fills it is irregularly distributed, having several stripes 

 or wisps in it ; and there are four stars near it, besides the one 

 figured by Sir John Herschel in his catalogue of nebulae. It is also 

 worthy of notice, that this nebula, instead of that regular outline 

 which he has there given it, is fringed with appendages, branch- 

 ing out into the surrounding space, like those of 13 Messier, and in 

 particular, having prolongations brighter than the others in the di- 

 rection of the major axis, longer than the ring's breadth. A still 

 greater difference is found in 1 Messier, described by Sir John Her- 

 schel as "a barely resolvable cluster," and drawn, fig. 81, with a 

 fair elliptic boundary. This telescope, however, shows the stars as 

 in his figure 89, and some more plainly, while the general outline, 

 besides being irregular and fringed with appendages, has a deep bifur- 

 cation to the south. 



From these and some other discrepancies, Dr. Robinson thinks it 

 of great importance that the globular nebulae and clusters should be 

 all carefully reviewed, as it is chiefly from their supposed regularity 

 that the hypothesis of the condensation of nebulous matter into suns 

 and planets has arisen ; an hypothesis which he thinks has, in some 

 instances, been carried to an unwarrantable extent. 



On the whole, he is of opinion that this is the most powerful 

 telescope that has ever been constructed. So little has been publish- 

 ed respecting the performance of Sir W. Herschel's forty-foot tele- 

 scope, that it is not easy to institute a comparison with that, the only 

 one that can fairly be made to compete with it. But there are two 

 facts on record which lead to the inference that it was deficient in 

 defining power : one, the low power used, which Dr. Robinson thinks 

 was not above 370 ; the other, the circumstance that neither the fifth 

 nor sixth stars of the trapezium of the nebula of Orion were shown by 

 it. As to light, there is no reason to believe that the composition of 

 the forty-foot mirror was as reflective as that of the twenty-foot ; and 

 if Dr. Robinson be correct in the opinion, that the latter* did not show 

 the fifth star easily, or the sixth at all, and that it only exhibited the 

 " debilissima" and one star near the ring-nebula, then it has decidedly 

 less illuminating power than eighteen, perhaps not more than fourteen 

 inches aperture of Lord Oxmantown's mirror, notwithstanding the 

 loss of light in that by the reflexion at the second speculum. 



However, any question about this optical pre-eminence is likely 

 soon to be decided, for Lord Oxmantown is about to construct a 

 telescope of unequalled dimensions. He intends it to be six feet 

 aperture and fifty feet focus, mounted in the meridian, but with a 

 range of about half an hour on each side of it. If he succeeds in 

 giving it the same degree of perfection as that which he has attained 

 in the present instance, which is exceedingly probable, it will be in- 

 * In its original state, not as improved by the more perfect means latterly 

 employed by Sir John Herschel, 



