On the improved Dividing Engine. 369 



an obscure publication ; — a writer who, I presume to pre- 

 dict, will not venture to claim in his own name the merit 

 that may be due to his luminou-s retrospections. 



About ten years back I made a dividing engine, nearly 

 29 inches in diameter, now in the possession ot'Mr. Cook of 

 Shadwell, in making of which I met with difficulties of 

 which none can torm an idea but tho^e who have attempted 

 to make dividing engines; — difficulties which are now al- 

 most entirely removed by the new method that I have con- 

 trived. ]n the first place, in making the former engine I 

 turned a rabbet on the ediie to receive a ring of plate brass, 

 in which the teeth were cut ; but after I had racked it, that 

 is cut the teeth, I was not satisfied, I took it off and put 

 on a second, which experienced the same fate. 1 then put 

 on a third, and cut it by divisions with a single cutter, h\ 

 the same way that a clock-wheel is cut, and then applied 

 the screw-cutter to regulate the Iteth. I found that by 

 , this method I got nearer to truth than I did in the two 

 former rings. In fact, I found that I got it as true as other 

 engines are in general. But though I did a good deal of 

 dividing for the trade, and even gave general satisfaction to 

 my customers, still I conceived that soine method or con- 

 trivance miaht be discovered by which the truth of the teeth 

 would be self-evident. I thought that if I could fix a second 

 screw-cutter directly opposite, and coininunlcate exact mo- 

 tion to both at the same time, this would in a great measure 

 answer tl)e purpose; (on this method I had many conver- 

 sations with Mr. Jarvis, die-sinker, New-street Hill, Shoe- 

 lane ;) but alter long consideration, and for many reasons 

 that would be too tedious to n)ention here, I was obliged to 

 give up the idea as impracticable in my opinion. However, 

 I did not despair; I still entertained hopes oF devising some 

 method whereby the teeth of a dividing engine could be cut 

 to a greater degree ol' certainty than hitherto had been done; 

 and also upon a self-evident principle, that would exclude 

 everv degree of doubt respecting its accuracy. 



At length a new idea presented itself to my mind, which 

 was, to make a second wheel act on the same centre or axis, 

 to afford me an opportunity to shilt the one half oF the rack 

 or teeth to different parts of the circle, when under the 

 operation of cutiinu, the teeth. The screw-cutter being fixed 

 so .IS to cut halFot the teeth in the one ring, and half in the 

 other, I directly saw that this method woidd afford mc aix 

 opportunity of examining the error of the teeth, and also 

 give the cutter an opportunity to correct errors. The n»ore 

 I thought of tliis method the belter 1 liked it ; but I saw, 



Vol.40. No. 173. A^ot'. 1812. A a also. 



