A REFRACTING TELESCOPE WITH A FLUID CONCAVE LENS. 41 



Tlie front socket is different from the others, as it forms one piece with an 

 upright socket which carries a strong oaken stancheon, to the upper part of 

 which the machinery described below is attached. This stancheon having to 

 support a great part of the weight of the telescope, at least in some positions 

 of the latter, is strongly braced back by an oaken beam to the opposite ledge 

 of the triangular base. 



The principal upright part of the stand are two oaken bars framed or 

 secured together in the middle and on the top, and turning on strong iron bolts 

 in two cast-iron ears below ; about which bolts this part, called the swinging 

 frame, has a motion. These bars are cased on the outside by grain-cut oaken 

 facings, and thus form two grooves in which an interior frame slides freely. This 

 frame, on one of its interior sides carries a fixed racket, not seen in the plate, 

 its whole length ; and between the two connecting pieces in the centre of the 

 swinging frame, is a spring pall which catches each tooth of the racket as 

 it passes, being intended to prevent any accident in case of the breaking of 

 a rope when the telescope is elevated. 



To the pall is attached a string which descends near the upright stancheon; 

 and when it is necessary to let down the telescope, this string is pulled by one 

 hand, and the other having hold of the proper apparatus, the descending mo- 

 tion takes place in the most gentle and easy manner possible. 



On the upper part of the front upright stancheon are two strong wrought- 

 iron checks, terminating about two inches above it, having two circular holes 

 l^ths of an inch diameter, in which turns, as in two collars, a strong iron screw 

 14 inch in diameter, having two threads to the inch : on this works a strong 

 brass nut with corresponding threads, and to this nut the frame which carries 

 the telescope, and is called the bearing frame, is properly united, turning on a 

 moveable joint near the screw. The screw is turned by four long cross han- 

 dles, seen in the plate, by means of which the azimuth motion of a star or 

 planet is followed. The length of the screw is about 11 inches and of the nut 

 3 inches, leaving a motion of 8 inches, which enables a star to be followed 

 for a considerable time without moving the stand : the turning point on which 

 this motion of the frame takes place, is exactly in the centre of the upper part 

 of the interior or sliding frame, where a pin is fixed, which traverses in a 

 parallel groove under the bearing frame ; but to prevent confusion this is not 

 shown in the plate. 



MDCCCXXIX. a 



