11 



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

 powerful telescope that has ever been constructed. So 

 little has been published respecting the performance of Sir 

 W. Herschel's forty-foot telescope, 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. R. 

 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 shewn 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. R. be correct in the opinion, that the latter* did not 

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

 exhibited the " debilissima" and one star near the ring-ne- 

 bula, 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 in- 

 tends 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, indeed, a 

 proud achievement; his character is an assurance that it 

 will be devoted, in the most unreserved manner, to the ser- 

 vice of astronomy, while the energy that could accomplish 



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

 employed by Sir John Herschel. 



