50 Mr Dick's Description of a New Reflecting Telescope^ 



position, which were found necessary in the construction of Dr 

 Herschers large reflecting telescope *. With regard to telescopes 

 ^^ Waller dimensions, as from 5 to 15 feet focal length, with the 

 exception of the expence of the specula and eye-pieces; they 

 might be fitted up for a sum not greater than from 2 to 5 or 6 

 guineas. 



Were any person to attempt the construction of these tele- 

 scopes, in the mean time, it is not hkely he would succeed, with- 

 out more minute directions than I have yet given. The astro- 

 nomical eye-pieces used in the aerial telescope, have a particUar 

 modification, which is essentially requisite to distinctness of vi- 

 sion ; and, therefore, were any one to try the experiment with a 

 common astronomical eye-piece, he would most probably feel 

 disappointed in the performance of the instrument. A descrip- 

 tion of the peculiarity of the eye-piece to which I allude, with 

 other particulars in relation to these instruments, I deem it ex- 

 pedient, for certain reasons, to postpone to a future opportu- 

 nity. 



I have sometimes used these instruments for the purpose of 

 viewing perspective prints, which they exhibit in a beautiful and 

 interesting manner. If a coloured perspective be placed at one 

 ■end of a large room, and strongly illuminated with two candles, 

 and one of those reflectors, furnished with a small magnifying 

 power, placed at the opposite end of the room, the representation 

 of a street or a landscape will be seen in its true perspective, 

 and will appear even more pleasant and interesting than when 

 viewed through the common optical diagonal machine. If an 

 inverting eye-piece be used, which is most eligible in this expe- 

 riment, the print, of course, must be placed in an inverted posi- 

 tion. 



That reflecting telescopes of the description now stated are 

 original in their construction, appears from the uniform language 

 of optical writers, some of whom have pronounced such attempts 

 to be altogether impracticable. Dr Brewster, one of the latest 



• The idea here suggested will perhaps be more readily appreciated, by an in- 

 spection of Plate I. Fig. 3, where A is the short tube, BC and DE the two large 

 bars or arms, connected with cross bars, for the purpose of securing strength 

 and steadiness. At F and G, behind the speculum, weights might be applied, 

 tf necessary, for counterbalancing the lever-power of the long arm. 



