THE RAMSDEN DIVIDING ENGINE. 737 



fitted to the half holes F aud T, which were kept together by the 

 screws Z. 



H represents a screw of untempered steel, having a pivot, 1, which 

 runs in the hole K. At the otner end of the screw is a hollow center, 

 which receives the hardened conical point of the steel i)iu M. When 

 this point is sufficiently pressed against the screw to prevent its shak- 

 ing the steel pin may be fixed by tightening the screws Y. 



N is a cylindric nut. movable on the screw 11, which, to prevent any 

 shake, may be tightened by the screws O. This nut is connected with 

 the saddle piece P b\' means of the intermediate universal joint IF, 

 through which the arbor of the screw 11 passes. A front view of this 

 piece, with a section across the screw arbor is rei)resented at A". This 

 joint is connected with the nut by means of two steel sii[)s, 8, which 

 turn on pins between the cheeivs T on the nut N. The other ends of 

 these slips, S, turn in like manner on pins [a). One axis of this joint 

 turns in a hole in the cock (/>), wliich is hxed to the saddle piece, and 

 the other turns in a hole, (d), made for that purpose in the same piece 

 on which the cock (b) is tlxed. By this means, when the screw is 

 turned round, the saddle piece will slide uniformly along the triangu- 

 lar bar A. 



Having measured the circumference of the dividing wheel, I found 

 it would require a screw about one thread in a hundred coarser than 

 the guide screw 11. The wheels on the guide screw arbor //, and that 

 on the steel E, on which the screw was to be cut, were proportioned to 

 each other to produce that effect by giving the wheel (L) 198 teeth and 

 the wheel [Q) 200. These wheels communicated with each other by 

 means of the intermediate cogwheel li, which also served to give the 

 threads on the two screws the same direction. 



K is a small triangular bar of well-tempered steel, which slides in a 

 groove of the same form on tiie saddle i)iece P. The point of this bar 

 or cutter is formed to the shai)e of the thread intended to be cut on the 

 endless screw. When the cutter is set to take proper hold of the 

 intended screw it may be fixed by tightening the screws {e), which 

 press the two pieces of brass, G, upon it. 



The saddle i)iece Pis confined on the bar A by means of the pieces 

 {(j}j and may be made to slide with a i)r()per degree of rightness by the 

 screws (n). 



RAM.SDEN GltADUATES THE GREAT TIJEODOEITE NOW AT GREENWICH. 



In 1 785 Mr. Kamsdeu was re(piested " to make an instrument for meas- 

 uring horizontal angles witli more precision than the ordinary theodo- 

 lite." It was with this dividing engine that Kamsden graduated this 

 instrument known as ''the great theodolite," still preserved at Green- 

 wich, for the trigonometrical survey of Great Britain, described in Vol. 

 80, Philosophical Transactions. 



One of the first projects of the trigonometrical survey of Great Britain 

 H. Mis. 129 47 



