In the Observatory of Dor pat. 107 



every 10'; but which, by a vernier, may be read off to 5". 

 At the other end, the box or frame in which the tube lies, is 

 fixed by means of twelve screws. 



The tube itself is 13 feet long, constructed of deal, in 

 the strongest and safest manner, and overlaid with maho- 

 gany, so worked, that it appears like a tube of highly-burnish- 

 ed copper. The object-glass and eye-pieces are set in metal 

 frames, and provided with adjusting screws for the purpose 

 of bringing the axes of the glasses into one straight line. 



The diameter of the object-glass is nine Paris inches. The 

 Finder attached to the tube, is an achromatic telescope of 30 

 inches focus, and 29 lines diameter, set in metal. 



Two counterpoises, fixed to levers, prevent the object-end 

 of the telescope from overbalancing the other end, and at the 

 same time secures it from bending, since they are fixed on the 

 same principle as the counterpoises, which, in Reichenbach's 

 meridian circles, counteract the effect of the weight on the 

 tube, with this difference, that, in our instrument, the levers 

 turn round double axes on account of the changes in the po- 

 sition of the tube. 



Two other counterpoises, (one of which is fixed to a strong 

 iron axis turning by means of a double ring round the frame 

 of the axis which lies parallel to the equator, and the other 

 on the end of this axis itself,) serves to remove the weight 

 resting on the polar axis, and at the same time to diminish 

 the friction of the second in its frame. Another counter- 

 poise supports the polar axis just in the centre of gravity of 

 all the moveable parts of the instrument, by means of two 

 friction-rollers, by which the turning of the whole round the 

 polar axis is effected with the greatest facility. 



The instrument, after being thus set up, and the counter- 

 poise properly adjusted, is perfectly balanced in every situa- 

 tion. It may be turned in declination with the finger, and 

 round the polar axis with still less force, a weight of three 

 pounds being fixed at some distance from the eye-end, by 

 which the friction is overcome. Thus, this enormous tele- 

 scope may be turned in every direction towards the heavens, 

 with more ea6e and certainty than any other hitherto in use. 



