10 •N DIVIDING INSTRUMENTS. 



a four feet meridian circle, now the property of StepheB 

 Groombridge, Esq., of Blackheath. 



A5soaibed. The surface of the circle which is to receive the divisions, 



as well as its inner and outer edges, but especially the lat- 

 ter, should be turned in the most exact and careful man- 

 lier; the reason for which will be better understood, when we 

 come to describe the mode of applying the roller: and, as no 

 projection can be admitted beyond the limb, if the tele- 

 scope, as is generally the case, be longer than the diameter, 

 those parts which extend farther must be so applied, that they 

 may be removed during the operation of dividing. Fig.l, Pl.I, 



Apparatus. and 2, PI. II, represent the principal parts of the apparatus; 

 Fig. I showing the plan, and Fig. 2 the elevation; in both 

 of which the same letters of reference are affixed to corre- 

 sponding parts, and both are drawn to a scale of half di- 

 mensions. A A is a part of the circle, the surface of which 

 is seen in the plan, and the edge is seen in the elevation, 

 BJBB is the main plate of the apparatus, resting with its 

 four feet aaaa upon the surface of the arc; these feet, 

 being screws, may be adjusted so as to take equal shares of 

 the weiglit, and then are fastened by nuts below the plate, 

 as shown in Fig. 2. C C and DD are two similar plates, 

 each attached to the main plate, one above and the other 

 below, by four pillars; and in them are centred the ends 

 of the axis of the roller E. F and G are two friction 

 wheels, the latter firmly fastened to B, but the former is 

 fixed in an adjustable frame, by means of which adjust- 

 ment these wheels and the roller E, may be made to press; 

 the former on the interior, and the latter on the exterior 

 edge of the circle, with an equal and convenient force*. 

 At the extremities of the axis of the roller, and attached to 

 the middle of the plates C and D, are two bridges, having 

 a screw in each ; by means of whi(;h an adjustment is pro- 

 «ured for raising or lowering the roller respecting the edge 



♦ Sufficient spring for keeping the roller in close and uniform contact 

 ■with the ed};e of the circle is found in the apparatus, without any par- 

 ticular contrivance for this purpose ; the bending «f the pillars of the 

 secondary frames and of the axis of the roUa chiefly supj)li«s this pro- 

 perty, 



of 



