of Achromatic and Reflecting Telescopes. 311 



I have seen the nebulae in Orion ; the planets Jupiter and 

 Saturn, with the Paris telescope ; and with their appearances 

 in Mr HerschePs twenty feet reflector, I am perfectly fami- 

 liar, and the comparison is many times in favour of the latter. 



The power of the twenty feet reflector at Slough is well 

 authenticated ; and if the indefatigable astronomer of Dorpat 

 will turn his probably matchless achromatic upon some of the 

 faint nebulae in the constellation Virgo, or upon some others, 

 not easily resolvable into stars, he will soon satisfy himself, 

 that his ideas of its space penetrating power are much over- 

 rated. 



The star Z, Bootis was seen " close double" by Mr Pond 

 at Lisbon, perhaps twenty years ago,* and, as I believe, with 

 a Newtonian reflector of six inches aperture, and the circum- 

 stances mentioned in a letter written by him to Dr Wollas- 

 ton. The instrument with which I first observed it, in 1810, 

 " close double," was a reflector of the worst possible construc- 

 tion, viz., a Gregorian reflector of six inches aperture, and 

 thirty inches focal length, but a very perfect instrument, made 

 for me by Mr Watson in the year 1809, and which is now 

 in the possession of my friend Mr Perkins." 



After speaking of the merits of the telescope of M. Lere- 

 bours, Mr Herschel proceeds as follows : 



" My object in writing this, is to obviate an erroneous im- 

 pression that may arise in the minds of those who read Mr 

 Fraunhofer 1 s Memoir, as to the great inferiority of reflecting 

 telescopes in point of optical power to achromatics in general, 

 and more especially to those constructed with such delicacy 

 as his own doubtless are. Those who have witnessed th e 

 performance of M. Amici's beautiful Newtonian reflector 

 will not readily admit this inferiority, but will feel disposed 

 to wish that some attempt might be made to accommodate 

 such admirable instruments to the more exact purposes of as- 

 tronomy, an object which appears to have been too easily lost 

 sight of. 



" Mr Fraunhofers expressions, when speaking of the loss of 

 light by metallic reflection, arc, I think, too strong. He 

 observes, that ' the most perfect metallic mirror reflects only 

 • See Scientific Intelligence, Asikonomy, § 1.— Ed. 



