42 Mr Dick's Description of' a neio Reflecting Telescope, 



in length, of a form somewhat different from th^^t proposed by 

 Gregory, which he presented to the Royal Society : But we 

 hear no more about the construction of reflectors, till the year 

 1723, when MrHadley published^ in No. 376 of the Philosophi- 

 cal Transactions, an account of a large Newtonian reflector, 

 which he had just then constructed, and which left no room to 

 fear that this invention would remain any longer in obscurity. 

 The large speculum of this instrument was 62| inches focal dis- 

 tance, and 5§ inches diameter, was furnished with magnifying 

 powers of from 190 to 230 times, and equalled in performance, 

 the famous aerial telescope of Huygens of 123 feet in length *. 

 Since this period, the reflecting telescope has been in general 

 use among astronomers in most countries of Europe, and has 

 received numerous improvements, under the direction of Short, 

 Mudge, Edwards and Herschel, the last of whom constructed 

 reflectors of 7, 10, 20, and even 40 feet in focal length, which 

 far surpassed in brightness and magnifying power, all the instru- 

 ments of this description, which had previously been attempted. 

 Having constructed and made a variety of experiments on 

 small Gregorian reflectors, I was generally disappointed in my 

 expectations of the effects produced by their performance ; and 

 had always recourse to achromatic telescopes, both in terres- 

 trial and celestial observations, where brightness, distinctness and 

 accuracy, were required. This might be owing, in part, to a de- 

 ficiency in the figure and polish of the specula I made use of 

 in these instruments ; but in all the Gregorian telescopes I have 

 had occasion to use, there is a certain degree of dinginess and 

 obscurity, which renders their performance less pleasant, and 

 far inferior to that of good achromatic refractors. About four 

 years ago, an old speculum, 27 inches in focal distance, very im- 

 perfectly polished, having accidentally come into my possession, 

 and feeling no inclination to fit it up in the Gregorian form, I 

 formed the resolution of throwing aside the small speculum, and 

 attempting the front view, notwithstanding the uniform asser- 

 tion of opticians, that such an attempt in instruments of a small 

 size is impracticable. I had some grounds for expecting suc- 



* A particular description of this telescope, with the machinery for moving it, 

 illustrated with an engraving, may he seen in Reid and Gray's " Abridgment of 

 the Phil. Transactions," vol. vi. part i. p. 147. 



