THE RAMSDEN DIVIDING ENGINE. 735 



carefully pressed against the circumference of the wheel by turning 

 the finger-screw; then, removing the clamp, I turned the screw by its 

 handle 9 revolutions, till the intersection marked 240 came nearly to 

 the wire ; then, unturning the finger-screw, I released the screw from the 

 wheel and turned the wheel back till the intersection marked 2 exactly 

 coincided with the wire, and by means of the clamp before mentioned, 

 the division 10 on the circle being set to its index, the screw was pressed 

 against the edge of the wheel by the finger-screw ; the clamps were re- 

 moved, and the screw turned 9 revolutions till the intersection marked 1 

 nearly coincided with the fixed wire; the screw was pressed, as before, the 

 wheel was turned back till the intersection 3 coincided with the fixed wire; 

 the division 10 on the circle being set to its index, the screw was pressed 

 against the wheel as before, and the screw turned 9 revolutions till the 

 intersection 2 nearly coincided with the fixed wire, and the screw was 

 released ; and I jiroceeded in this manner till the teeth were marked 

 round the whole circumference of the wheel. This was repeated three 

 times round, to make the impression of the screw deeper. I then 

 ratclied the wheel round continually in the same direction without 

 ever disengaging the screw, and in ratching the wheel about 300 times 

 round the teeth were finished. 



"l!5ow it is evident, if the circumference of the wheel was even one 

 tooth or ten minutes greater than the screw would require, this error 

 would in the first instance be reduced to one-two-hundred-and-fortieth 

 part of a revolution or two seconds and a half; and these errors or in- 

 equalities of the teeth were equally distributed round the wheel at the 

 distance of 9 teeth from each other. Now, as the screw in ratching had 

 continually hold of several teeth at the same time, and these con- 

 stantly changing, the above-mentioned inequalities soon corrected 

 themselves and the teeth were reduced to a perfect equality. 



" The piece of brass which carries the wire was now taken away and 

 the cutting screw was also removed and a plain one (hereafter described) 

 put in its place. On one end of the screw is a small brass circle, having 

 its edge divided into 60 equal parts and numbered at every sixth division, 

 as before mentioned. On the other end of the screw is a ratchet wheel 

 having 60 teeth, covered by the hollowed circle, which carries two 

 clicks that catch upon the opposite sides of the ratchet when the screw 

 is to be moved forward. 



"The cylinder turns on a strong steel arbor, which passes through 

 and is firmly screwed to the piece Y. This piece, for greater firmness, 

 is attached to the screw-frame by braces ; a spiral groove or thread is 

 cut on the outside of the cylinder, which serves both for holding the 

 string and also giving motion to the lever on its center by means of a 

 steel tooth that works between the threads of the spiral. To the lever 

 is attached a strong steel pin on which a brass socket turns. This 

 socket passes through a slit in the piece, and may be tightened in any 

 part of the slit by the finger-nut. This piece serves to regulate the 

 number of revolutions of the screw for each tread of the treadle. 



