1 70 Mechanical Instrument to work Edition of Numlers. 



moveahle on a centre pin attached hy a stud H to the lower 

 circle BB, and its tail is pressed by a small spring h, which 

 causes it to press constantly upon the under side of the 

 great circle A A, and produces such a friction as prevents 

 the upper circle slipping loosely round; a screw k, fig. 3, 

 is fixed in one part of the under side of the lower circle, so 

 that in turning round it intercepts the detent G, and in this 

 position the edge of the index PP is at the zero, or point 

 of commencement of all the numbered circles. In this 

 position the instrument is ready for use, in the following 

 planner : suppose the following sum is to be added up ; 



£• s. d. 



134 16 9 



Having adjusted the instrument as before described, thait 

 is, having brought the circle to the zero, hold the circle 

 BB in the one hand, and take the end L of the lever 

 CL in the other: then move the end of the lever CL till 

 its edge c cuts the figure 4 of the limb FF, which is the 

 first figure in the sum : in this movement the index is held 

 up so as not to touch the teeth ; but having arrived at the 

 intended figure, it is pressed down into the teeth, and is 

 brought back again (the circle with it) until it touches the 

 stop by when it will have moved the circle, so that 4 stands 

 before the index P on the pence circle ; then the index L 

 is carried back again to 3, the second figure of the sum, 

 and returned to its stop, carrying with it three divisions 

 more; it is next moved to 5, and so on, following the 

 pence column till the numbers at the top is counted; 

 then, examining at the edge of the index PP, it will be 

 found to stand at 9, in the pence circle, and the nearest 

 red figure which has passed by the index will be 1, denot- 

 ing 1 shilling and 9 pence; therefore 9 must be put down, 

 and 1 carried to the next column : and to recollect this, a 

 small pin, x, must be stuck into the hole No. 1, upon the 

 outside of the hml) F: the circle is then returned to the 

 zero, which is readily performed by turning it backwards 

 as far as it will go, and the stop k, fig. 3, prevents its going 

 further than the right position : the column of shillings is 

 then added up by the same process, taking the numbers 3, 



4,, 6, 



