THE RAMSDEN DIVIDING ENGINE. 737 



fitted to the biilf holes F and T, which were kept together by the 

 screws Z. 



II represents a screw of imtempered steel, having a pivot, J, which 

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

 which receives tlie hardened conical point of the steel pin 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. 



JV is a cyliudric nut. movable on the screw H, which, to prevent any 

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

 the saddle piece P by means of the intermediate universal joint W, 

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

 piece, with a section across the screw arbor is represented atX. This 

 joint is connected with the nuL by means of two steel slips, /8', which 

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

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

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

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

 on which the cock (6) is fixed. 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 H. The wheels on the guide screw arbor i/, and that 

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

 each other to produce that etiect by giving the wheel [L) 198 teeth and 

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

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

 threads on the two screws the same direction. 



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

 groove of the same form on the saddle piece P. The point of this bar 

 or cutter is formed to the shape 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 (d), which 

 press the two pieces of brass, (r, upon it. 



The saddle piece Pis confined on the bar A by means of the pieces 

 (</), and may be made to slide with a proper degree of rightness by the 

 screws (w). 



RAMSDEN GRADUATES THE GREAT THEODOLITE NOW AT GREENWICH. 



In 1785 Mr.Ramsden was requested " to make an instrument for meas- 

 uring horizontal angles with more precision than the ordinary theodo- 

 lite." It was with this dividing engine that Eamsden 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 



