Mr. Herschel on Reflecting Telescopes. 291 



Fraunhofer concludes that the power of the telescope was in- 

 sufficient to resolve it, and must therefore have been inferior to 

 that of an achromatic in the hands of Mr. Bessel, with which it 

 was recognised by that eminent astronomer as double. It will be 

 seen on reference to the Memoir on double stars lately published 

 in the Philosophical Transactions by Mr. South and myself, that 

 this star had been long since ascertained to be double, not only by 

 Mr. Bessel, but by Messrs. Struve, Pond, and South, and, what is 

 more to the present purpose, by Sir William Herschel himself. 

 It was only by oversight that we omitted to refer in that work to 

 his account of it, which is published in his paper " On the places 

 of 145 new double Stars," in the first volume of the Transactions 

 of the Astronomical Society, page 178. Which paper was read on 

 June 8, 1831. It will not be amiss if we extract the account 

 verbatim. 



" (114). Journal, April 5, 1796.— 7 feet reflector power 460 

 (£) Bootis double 1st class. Very nearly in contact ; I can, how- 

 ever, see a small division. A little unequal, the preceding is the 

 smallest." 



" Rev. Aug. 6, 1796. f Bootis. double. Position 2 Rev.— 

 14.5 parts + 1.1 for Zero — 41° 59'. 1 np. With 460 a division is 

 but barely visible \ of S. Both w. A little or pretty unequal." 



" Rev. July 12. 1807. f Bootis. They are fine, equal, whitish 

 stars : the interval between their apparent discs with 460 is £ of 

 the diameter of either." 



To these observations I will only add, that with the same tele- 

 scope, but with a mirror much tarnished, and now used only for the 

 most ordinary observations, I last night saw this star, as well as 

 <r Coronae and tj Coronae, distinctly double. 



The argument, then, from the omission of this star, is untenable, 

 f Orionis would have furnished a case much more in point. The 

 very singular history of this star will be found in the Memoir on 

 double Stars already mentioned. 



In large reflectors, in which only one metallic mirror is used, 

 the disadvantage in point of light under which they labour, in 

 comparison with refractors, is however much less formidable. 



