54 



Dr. Ure on the Specula of Telescopes. 



tangentially from it. On this a key is fitted to the inner surface 

 of the folding lid, to V^liich two slender springs are affixed. 

 When the telescope is placed at an elevated angle, these springs 

 prevent the lateral segments of the cover from falling forwards, 

 or striking against the face of the mirror. These springs are 

 not, however, so stiff as to hinder the cover from folding down 

 to the wooden surface of the tube by its weight. At the top 

 of the box, there is a spring catch (detent) fixed, to prevent the 

 lid from falling oflP. The speculum box (frame) is attached to 

 the end of the wooden tube, by resting in a step at the bottom ; 

 and having two screws to adjust its inclination to the axis, in 

 the same way as adopted by Sir William Herschel. When in 

 its place, the prismatic iron rod stands opposite to a hole in 

 the tube, by which the key is introduced to open or cover up 

 the mirror. A small sliding plate shuts up this hole. 



Fig. 1, represents the speculum uncovered, with the lid 

 lying against the under surface of the tube. The dotted 

 lines are a section of the tube. A the speculum, B the box, 

 C the lid, D the spring catch to hold the lid in its place. E 

 the square rod, for the key to open it by. Fig. 2, shews the 

 speculum box shut up, and fixed in the end of the wooden 

 octagon by the adjusting screws, as at F. 



We are, Sir, your obedient servants, 

 To Dr. Ure. (Signed,) John and Robert Haut. 



Fig. I. 



Fis. II. 



D 



